This Section proposes the simplest scheme for finding out the causes of malfunctions and failures occurring in the components and systems of the vehicle. Failures and their possible causes are divided into groups based on their relation to certain components or systems of the car, such as engine, cooling system, etc., in addition, the text provides links to Chapters and Sections related to these problems.
Remember that successfully completing a root cause troubleshooting is not black magic reserved for experienced professional mechanics, but is determined by a combination of specific knowledge and a patient, systematic approach to investigating the problem. You should always move from simple to complex, bring each check to its logical conclusion and try not to miss obvious facts - anyone can forget to fill the fuel tank or leave lights on at night.
Finally, you should always try to get a clear picture of the development of the malfunction and take appropriate steps to prevent recurrence. If the failure of the electrical equipment occurred due to a violation of the quality of the contact, check at the same time the condition of all other contacts and electrical connectors of the system. If the same fuse continues to blow several times in a row, there is no point in replacing it further - you must try to find out the cause of the failure. Remember that the failure of a minor component may be a sign of a malfunction of a more important node or the entire system.
Engine won't crank when trying to start it
1. The battery terminals are corroded or the wire ends are loose. Check the condition of the terminals and lugs. Tighten the terminal clamps, if necessary, remove traces of corrosion.
2. Discharged or defective battery. If the wire lugs are found clean and securely attached to the battery terminals, turn the ignition key to the ON position, then turn on the headlights and/or windshield wipers. If this electrical equipment does not function, the battery is dead.
3. Transmission is not correctly set in position «R».
4. The wiring in the starting system circuit is broken or the wires are loose on the terminals. Check the condition of the wires, terminals and electrical connectors of the battery, the starter traction relay and the ignition switch.
5. The starter gear is stuck in the ring gear of the drive disc. Try to crank the engine by the crankshaft pulley. At the first opportunity, remove the starter and check the condition of the gear and ring gear.
6. Defective starter relay (see chapter Engine electrical equipment).
7. Faulty starter (see chapter Engine electrical equipment).
8. Faulty ignition lock.
Engine cranks but won't start
Petrol models
1. Wrong startup (see the relevant Chapter Section Manual).
Attention! Starting procedure for a gasoline engine:
- Engage the parking brake.
- Engage neutral (RKPP) / move the selector lever to position «R» or «N» (AT).
- Without depressing the gas pedal, turn the key in the ignition switch to the right until it stops. Release the key as soon as the engine starts. If a warm engine cannot be started by cranking it with the starter for more than 4 seconds, slowly depress the gas pedal. Do not crank the engine for more than 30 seconds in a row. Wait at least 15 seconds before trying again.
- Watch the engine oil pressure gauge (see the relevant Section in Chapter Manual): The pressure indicator should be activated immediately after starting. When the engine is very cold, the pressure display does not appear until some time after starting. Do not increase the engine speed until the oil pressure indicator is activated.
- At unstable speeds (e.g. misfires) To avoid damage to the catalytic converter, try to start the engine only for a short time and avoid heavy loads, - immediately drive the car to a Mercedes-Benz workshop.
- In areas where the outside temperature often drops below -20°C, the installation of a coolant heater is recommended. You can get help on this issue at any Mercedes-Benz service station.
2. Faulty or disabled engine immobilizer.
3. Defective fuse for electric fuel pump or electronic injection system (see chapter Onboard electrical equipment).
4. Empty fuel tank or poor quality fuel.
5. The air filter is very dirty. There are vacuum leaks in the air supply elements, malfunctions in the fuel injection and ignition control system.
6. Low battery (engine cranks too slowly). Check the functioning of the electrical equipment.
7. Battery terminal connections are corroded or loose.
8. The fuel pump is faulty, its fuse is blown, or the pump relay is damaged. Check the sound of the pump when the ignition is turned on (see chapter Power and exhaust systems).
9. Damaged or excessively wet components of the ignition system (see chapter Engine electrical equipment).
10. Worn or defective spark plugs or incorrect spark plug gap (see chapter Engine electrical equipment).
11. Broken or disconnected wiring of the electric circuit of the starting system or loosened fastening of the wires to the terminals.
12. Broken or disconnected ignition coil circuit wiring or loose wires at coil terminals (see chapter Engine electrical equipment).
13. Fuse 15 of the engine control unit is damaged, any of the sensors is faulty: Hall, impulse sensor, coolant temperature sensor (ECT) or intake air (IAT) (see chapter Onboard electrical equipment).
14. Compression pressure too low. Replace the cylinder head gasket. Repair the engine if necessary.
Diesel models
1. Wrong start.
Attention! Diesel engine start procedure:
- Engage the parking brake.
- Engage neutral (RKPP) / move the selector lever to position «R» or «N» (AT).
- Turn the key in the ignition switch to position 2, - the preheat indicator lamp on the instrument panel should light up (see the relevant Chapter Section Manual). The engine should be started no earlier than the control lamp goes out - without turning on the on-board consumers of electricity and without depressing the gas pedal, turn the key in the lock to the right until it stops.
- Attention! At an outside air temperature below -10°C, you should also squeeze the gas pedal to the stop. Continue cranking the engine with the starter until the engine speed stabilizes, but no more than 30 seconds. Before restarting after an unsuccessful attempt, remember to first return the key to position 0 and wait at least 15 seconds.
- Watch the engine oil pressure gauge (see the relevant Section in Chapter Manual) the pressure indicator should be activated immediately after starting. When the engine is very cold, the pressure display does not appear until some time after starting. Do not increase the engine speed until the oil pressure indicator is activated.
- If the preheat indicator lamp does not light up, then there is a malfunction in the preheat system, which must be repaired immediately by a Mercedes-Benz workshop.
- In areas where the outside temperature often drops below -20°C, the installation of a coolant heater is recommended. You can get help on this issue at any Mercedes-Benz service station.
2. Faulty engine immobilizer.
3. The fuse of the electric fuel pump or the preheat system is defective.
4. The engine is not warmed up: check the correct functioning of the preheater.
5. There is no voltage at the solenoid shut-off valve. Connect a voltmeter or an LED probe to the switch. Turn on the ignition. The LED should light up. Otherwise, you need to find a break in the wiring and fix it.
6. Faulty solenoid shut-off valve. Check the reliability of the fastening of the electromagnetic switch, check the contacts. Turn the ignition on and off. The switch should click.
7. There is damage in the fuel supply line or air in the lines:
- a) Pipelines or hoses are mechanically damaged or clogged, - clean the fuel pipes and remove air from the lines and the filter;
- b) The fuel filter is clogged, - replace the filter element;
- c) In winter, you should check the filter and pipelines for the presence of ice or wax, - drive the car into a heated garage, add gasoline to the system;
- d) Clogged tank vent or fuel intake strainer - clean.
8. The adjustment of the moment of the start of the fuel supply is knocked down. Check, make adjustments.
9. Faulty nozzles. Check. Loosen the union nuts in sequence - when the nut of the faulty cylinder is unscrewed, the engine speed will not drop.
10. Faulty high pressure fuel pump (injection pump). Install a new or known-good injection pump for testing.
11. Compression pressure too low. Replace the cylinder head gasket. Repair the engine if necessary.
The starter operates without cranking the engine
1. Stuck starter gear. Remove the starter (see chapter Engine electrical equipment) and check its status.
2. Worn or damaged starter gear teeth or flywheel crown.
Difficulty starting a cold engine
1. Discharged or insufficiently charged battery.
2. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
3. Paraffin in the diesel engine fine filter. Replace filter element. Refuel with winter fuel, or dilute with gasoline (refer to subsection Vehicle operation in winter conditions in Chapter Manual).
4. Faulty diesel engine glow plugs.
Difficulty starting a hot engine
See also Section Checking and adjusting the control position of the camshafts.
1. Blocked air filter (see chapter Power and exhaust systems).
2. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
3. Fuel does not reach the injection system injectors (see chapter Power and exhaust systems).
4. The fuel advance angle of the diesel engine has gone astray.
5. Low compression in the cylinders, the injection pump of the diesel engine is faulty or misaligned.
Starter engagement is too noisy or difficult
1. Worn or damaged starter gear teeth or flywheel crown.
2. Lost starter mounting bolts or loose tightening force.
Engine starts but immediately stalls
1. Faulty engine immobilizer.
2. Faulty wiring or loose wires at the coil or generator terminals.
3. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
4. The basic settings of the electronic control unit are violated (ECM).
5. Damage to the exhaust system/catalytic converter.
6. Vacuum loss occurs through the sealing surfaces of the intake manifold or fuel injection unit. Make sure that the fixing bolts/nuts are securely tightened, check the fact and quality of fastening on your fittings on the inlet pipeline of all vacuum hoses. Check the condition of the hoses and the correct connection (exactly to your fittings).
The stability of the engine at idle is broken
Petrol models
1. There are vacuum losses. Make sure that the fixing bolts/nuts are securely tightened, check the fact and quality of fastening on your fittings on the inlet pipeline of all vacuum hoses. Listen to the running engine with a stethoscope or a piece of fuel hose. The presence of a hissing sound will reveal the source «leaks» vacuum. No less effective can be used for checking a solution of soapy water.
2. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
3. Blocked crankcase ventilation valve (see chapter Engine).
4. Blocked air filter (see chapter Power and exhaust systems).
5. The fuel pump does not supply enough fuel to the injection system injectors (see chapter Power and exhaust systems).
6. There are leaks through the cylinder head gasket. Measure the compression pressure in the engine cylinders.
7. Camshaft lobes worn out (see chapter Engine).
Diesel models
1. The quality of the connections of the fuel hoses on the injection pump and the fuel filter is broken. Replace the fuel hoses, secure them with clamps, tighten the corner screws.
2. Mechanically damaged or loose fastening of the injection pump. Check fastening.
3. The connections of the return pipeline and the fuel supply pipeline are reversed. Put connections in place. The return pipe connection screw is marked «OUT».
4. There is damage in the fuel supply line:
- a) Pipelines or hoses are mechanically damaged or clogged, - clean the fuel pipes;
- b) Fuel filter clogged. Replace filter element.
- c) In winter, you should check the filter and pipelines for the presence of ice or wax, - drive the car into a heated garage, add gasoline to the system;
- d) Clogged tank vent or fuel intake strainer - clean.
5. The adjustment of the start of the fuel supply is knocked down. Check, make adjustments.
6. Faulty nozzles. Check. Loosen the union nuts in sequence - when the nut of the faulty cylinder is unscrewed, the engine speed will not drop.
7. Faulty high pressure fuel pump (injection pump). Install a new or known-good injection pump for testing.
There are misfires at idle
1. Worn or dirty spark plugs or incorrect spark plug gap (see chapter Engine electrical equipment).
2. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
3. Faulty spark plug wires (see chapter Engine electrical equipment).
4. Poor quality fuel filled. Fuel filter clogged.
5. There is a loss of vacuum in the intake manifold or through the hose connections.
6. Insufficient or unevenly distributed compression pressure in the cylinders. Take a compression test (see chapter Engine).
7. There are violations in the operation of the engine management system.
Misfire occurs while driving in gear
1. Blocked fuel filter or contaminated fuel system (see chapter Power and exhaust systems).
2. Faulty or dirty spark plugs or incorrect spark plug gap (see chapter Engine electrical equipment).
3. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
4. There is a defect in the spark plug wires (see chapter Engine electrical equipment).
5. Components of systems of decrease in toxicity of the fulfilled gases are faulty.
6. Insufficient or unevenly distributed compression pressure between the cylinders. Remove spark plugs and measure compression pressure (see chapter Engine).
7. Faulty ignition system (see chapter Engine electrical equipment).
8. Vacuum loss occurs at the throttle body, intake manifold, or through the vacuum hoses.
The engine spontaneously stalls
1. Idle speed adjustment is broken.
2. Blocked fuel filter and/or moisture or dirt in the fuel system (see chapter Power and exhaust systems).
3. There is a failure of the components of the power system or sensors (see chapter Power and exhaust systems).
4. Components of systems of decrease in toxicity of the fulfilled gases are faulty.
5. Faulty or dirty spark plugs or incorrect spark plug gap (see chapter Current service). Also check the condition of the spark plug wires (see chapter Engine electrical equipment).
6. There are vacuum losses at the throttle body or through the vacuum hoses.
The engine does not develop full power
1. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
2. Air cleaner clogged. Clean or replace.
3. Faulty spark plugs or incorrect spark plug gap (see chapter Current service
4. Faulty ignition coil (see chapter Engine electrical equipment).
5. Does not meet the requirements of the liquid level AT (see chapters Current service and automatic transmission).
6. Transmission slips (see chapter Clutch).
7. Blocked fuel filter and/or dirt/moisture in the fuel system (see chapter Power and exhaust systems).
8. Wrong grade of fuel filled. Fill the tank with fuel with the required octane rating.
9. Damaged turbocharger control valve
10. Faulty timing camshaft activator
11. Insufficient or uneven compression pressure across the cylinders. Carry out a compression test, the analysis of the results of which reveals the presence of valve leaks and / or a leak in the cylinder head gasket (see chapter Engine).
Optional for diesel engine
1. Air cleaner clogged. Clean or replace.
2. Uneven fuel supply of high-pressure fuel pump in cylinders. Adjust on a warm engine.
3. Incorrectly set the moment of the beginning of the fuel injection pump. Install.
4. Clogged fuel filter or injection pump (nozzle). Flush pre-filter, change fine filter element, clean sprayer or replace pump (nozzle).
5. Adjustment of the maximum frequency of rotation of the crankshaft is violated.
There are pops in the intake system or shots in the exhaust system
1. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
2. There is a defect in the secondary circuit of the ignition system (destruction of spark plug insulators or defects in spark plug wires) (see chapter Engine electrical equipment).
3. The fuel injection system needs adjustment or its components are excessively worn (see chapter Power and exhaust systems).
4. There is vacuum loss at the throttle body, intake piping, or through the vacuum hoses.
5. Stuck valves (see chapter Engine).
6. The order of connecting candle wires is violated (see chapter Engine electrical equipment).
Detonation sounds occur when accelerating or going uphill
1. Poor quality fuel filled.
2. There is a malfunction of the components of the power system or electrical equipment (see chapters Power and exhaust systems and Engine electrical equipment).
3. Wrong type spark plugs installed. Check spark plugs and coils for damage (see chapter Engine electrical equipment).
4. The basic settings of the electronic control unit are violated.
5. Faulty knock sensor.
6. There are vacuum losses.
There is an ignition (the engine continues to run after the ignition is turned off)
1. Excessively high idle (see chapter Engine).
2. There is a malfunction of the components of the power system or electrical equipment (see chapter Engine electrical equipment).
3. Damaged canister purge valve of the fuel vapor recovery system (EVAP).
4. Excessive engine operating temperature. Possible causes of this violation may be a decrease in the level of coolant (see chapter Cooling, heating systems), thermostat failure, radiator blockage, or water pump failure (see chapter Cooling, heating systems).
Diesel engine smokes
1. Black smoke:
- a) The air cleaner is dirty, - wash and refill with fresh oil or replace the element;
- b) Wrong fuel used, - flush the tank and change the fuel;
- c) Incorrectly set the moment of the beginning of the supply of high pressure fuel pump.
2. Blue smoke:
- a) Burning oil in the combustion chamber due to worn piston rings, high oil level in the air cleaner, worn seals in the turbocharger covers, leaks in the gasket between the crankcase and the turbocharger - repair the engine, set the normal oil level, replace the seals, tighten the turbocharger mounting bolts or replace gasket;
- b) Fuel is not supplied to one of the injectors, - check by heating the exhaust pipes of the manifold;
- c) Poor atomization of fuel by the injector due to a valve malfunction or a break in the atomizer - lap the valve or replace the injector.
3. White or brown smoke:
- a) Low temperature in the cooling system, - check the thermostat;
- b) Poor operation of nozzles due to wear or breakage of the atomizer - replace the atomizer.
Engine electrical equipment
Attention! Procedures of diagnostics of an electronic control system and codes of malfunctions are given in the Chapter Engine electrical equipment.
Battery not «keeps» charge
1. The alternator drive belt is worn or damaged, or its tension is not adjusted (see chapter Engine electrical equipment).
2. Insufficient electrolyte level or severely discharged battery (see chapter Engine electrical equipment).
3. The battery terminals are corroded or the wire lugs are loose on them (see chapter Engine electrical equipment).
4. The generator does not provide the required charge current (see chapter Engine electrical equipment).
5. Broken or otherwise damaged charging circuit wiring or loose wires at the terminals (see chapter Engine electrical equipment).
6. A short circuit in the electrical wiring creates a permanent leakage of current generated by the battery to «mass» (contact the head Engine electrical equipment and Schematic diagrams of electrical equipment).
7. There is an internal defect in the battery.
The charging indicator lamp does not go out when the rpm is increased
1. Loose drive belt. Check the V-belt tensioner.
2. Freewheel damage (only turbodiesel). Remove the generator and turn the generator drive shaft to the left. If the pulley face does not rotate, then the damage is usually in the freewheel.
3. Damage to the voltage regulator / generator. Disconnect the wire (D+) on the back of the generator and turn on the ignition. If now the control lamp does not light up, the fault is usually in the voltage regulator or in the generator.
4. Wear of brushes. Visually check the brushes, replace if necessary.
5. Regulator damage. Check, replace if necessary.
6. Damage to the generator. Check, replace if necessary.
7. Damage to the wire between the generator and the voltage regulator.
8. Damage to the instrument panel block.
The charging indicator lamp does not light up when the ignition key is turned to the ON position (when the ignition is turned on)
1. Burnt out or otherwise failed control lamp on the instrument panel (see chapter Onboard electrical equipment).
2. Faulty generator (see chapter Engine electrical equipment).
3. There is a defect in the printed circuit board, wiring inside the dashboard unit or lamp socket (see chapter Onboard electrical equipment).
The control lamp of a charge burns after switching off of ignition
The diodes are broken. Check diodes, replace diode board.
Starter
1. If the starter does not turn over, first check that the traction relay terminal 50 has the required voltage of at least 10 V. If the voltage is below this value, check the wires included in the starter current circuit according to the diagram.
2. Whether the starter operates at full battery voltage can be checked as follows:
- A) Without including gears, turn on the ignition;
- b) Bridge terminals 30 and 50 of the starter with a wire of at least 4 mm section2, refer also to Section «Checking the traction relay» Chapters Engine electrical equipment).
3. If the starter works flawlessly, the cause of the malfunction should be sought in the wires to the starter. If the starter does not work, it should be checked in the removed state.
Attention! Test condition: At the connection points, the wires must be well fixed and must not be oxidized.
The starter does not rotate when the ignition switch is turned on
1. Low battery. Charge the battery.
2. Bridge terminals 30 and 50 of the starter: The starter turns. Broken wire 50 to the ignition switch, the starter switch is faulty. Repair break, replace defective parts.
3. Breakage of the cable or ground connector, the battery is discharged. Check battery cables and connectors, measure battery voltage, charge if necessary.
4. Insufficient current flow due to loose or oxidized connectors. Clean battery poles and terminals, check connections between battery, starter and ground.
5. There is no voltage at terminal 50 of the traction relay. Broken wire, starter switch defective.
The starter rotates slowly and does not turn the crankshaft
1. Battery discharge. Charge the battery.
2. Filled with summer oil. Fill with multigrade oil.
3. Insufficient current flow due to loose or oxidized connectors. Clean battery poles and terminals, check connections between battery, starter and ground.
4. The carbon brushes are loose on the commutator, stuck in the guides, worn, broken, oily or dirty. Check brushes, clean or replace. Check guides.
5. Insufficient distance between brushes and commutator. Replace brushes and clean brush guides.
6. The collector is grooved or burnt and oily. Treat manifold or replace anchor.
7. No voltage at terminal 50 (min 8 V). Check the starter switch or traction relay.
8. Broken bearing. Check bearing, replace if necessary.
9. Faulty traction relay. Replace the traction relay.
The starter seizes and rotates the engine jerkily
1. Defective gear drive. Replace gear drive.
2. The gear is dirty. Clean the gear.
3. Faulty flywheel ring gear. Process the ring gear, if necessary, replace the flywheel.
Starter gear does not move away from crown
1. Gear drive or threads are dirty or damaged. Clean or replace gear drive.
2. Faulty traction relay. Replace the traction relay.
3. Return spring is weak or broken. Replace return spring.
The starter continues to work after the ignition key is released
1. The traction relay is stuck, does not turn off. Immediately turn off the ignition, replace the traction relay.
2. The ignition lock does not turn off. Disconnect the battery immediately, replace the ignition switch.
Supply system
Excessive fuel consumption
Petrol models
1. Dirty or blocked air filter element (see chapter Power and exhaust systems).
2. There is a malfunction of the components of the power system, electrical equipment or electronic control (see chapters Power and exhaust systems and Engine electrical equipment).
3. Leaks in the air intake system.
4. Damage to the exhaust system / catalytic converter.
5. Insufficient tire pressure or wrong size tires fitted.
Diesel engine
1. Clogged return line. Blow out the return line from the injection pump to the fuel tank with air.
2. Too high idle and maximum speed. Adjust.
3. The engine has mechanical damage. Check compression, repair engine if necessary.
There are fuel leaks and/or a smell of gasoline
1. There are leaks in the fuel lines or vent lines (see chapter Power and exhaust systems).
2. Fuel tank full. Refuel only until the gun automatically shuts off.
3. There are leaks or evaporation from the lines of the power system and reduce the toxicity of exhaust gases (see chapter Power and exhaust systems).
Engine won't start
1. When the starter is turned on, the electric fuel pump does not work (no noise from work). Tap the pump body lightly to loosen the stuck part. Check if voltage is being applied to the pump. Check fuse. Check electrical contacts for good conductivity.
2. Faulty fuel pump relay. Check the relay.
3. The emergency fuel switch under the driver's seat has been activated. Push the switch button.
4. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors. To do this, disconnect the injector connector. Attach a diode test lamp to the wire and turn on the starter. The control lamp should flash.
5. No signal from Hall ignition sensor or coolant temperature sensor. Check electrical wires. Interrogate the fault memory.
6. Damaged, clogged or leaking fuel lines, hoses are defective.
7. Clogged fuel filter.
8. Leaky intake system. Additional air is sucked in.
9. Damaged or leaking vacuum lines.
10. Damaged pressure regulator. Check residual pressure.
11. Damaged throttle position sensor.
12. There is no power supply to the electronic engine control unit.
13. Presence of ice or wax in the filter or lines of the diesel engine.
14. Clogged fuel tank ventilation, the filter in the tank is clogged.
15. The preheat does not work.
16. Damaged diesel engine fuel cut-off valve.
17. The moment of the start of the fuel supply is down.
18. Damaged diesel engine nozzles. Loosen the union nuts one by one and check if the corresponding cylinder works.
19. Faulty injection pump.
Cold engine starts badly, works unstably
1. The content of CO does not meet the requirements. Check CO content and idle speed.
2. Faulty coolant/intake air temperature sensor. Check sensor.
3. Fuel pressure does not match the required value. Check fuel pressure.
4. Leaky intake system. Additional air is sucked in.
Warm engine starts poorly, runs erratically
1. Leaky air intake system. Check intake system. To do this, leave the engine idling and cover the seals and connections on the intake tract with gasoline. If the speed increases for a short time, repair leaks.
Warning! Gasoline vapors are poisonous, do not inhale them.
2. Damaged fuel pump check valve.
3. Leaks in the fuel system.
4. Increased fuel pressure in the power system.
5. Malfunction of the fuel vapor recovery system.
6. Plugged or kinked fuel return line to tank.
7. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors. To do this, disconnect the injector connector. Attach a diode test lamp to the wire and turn on the starter. The control lamp should flash.
8. No signal from Hall ignition sensor or coolant temperature sensor. Check electrical wires. Interrogate the fault memory.
9. Leaky intake system. Additional air is sucked in.
10. Damaged or leaking vacuum lines.
11. Damaged pressure regulator. Check residual pressure.
12. Damaged throttle position sensor.
13. There is no power supply to the electronic engine control unit.
Engine runs intermittently
1. Electrical connections to the fuel pump are interrupted from time to time. Check the condition of the plug connections and connectors of the electrical wires of the fuel pump, air flow meter and fuel pump relay. Check the fuse and contact points on the fuel pump relay. Clean contacts, replace if necessary.
2. Poor fuel quality, vapor lock formation. Refuel with quality fuel.
3. Fuel supply too low. Check pump performance.
4. Defective fuel filter. Replace fuel filter.
5. Faulty fuel pump. Check fuel pump.
6. Faulty injectors. Check injectors.
7. The lambda probe is faulty, there are violations in the mixture quality control circuit or there is no heating of the lambda probe.
8. Faulty throttle position sensor. Check throttle position sensor.
9. Damaged exhaust manifold or exhaust pipe (there are exhaust leaks).
10. Malfunction of the fuel vapor recovery system.
11. The fastening of the fuel hoses to the injection pump and the fuel filter of the diesel engine has loosened.
12. When connecting, the supply and return pipelines of the injection pump were reversed.
13. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors. To do this, disconnect the injector connector. Attach a diode test lamp to the wire and turn on the starter. The control lamp should flash.
14. No signal from Hall ignition sensor or coolant temperature sensor. Check electrical wires. Interrogate the fault memory.
15. Leaky intake system. Additional air is sucked in.
16. Damaged or leaking vacuum lines.
17. Damaged pressure regulator. Check residual pressure.
18. Damaged throttle position sensor.
19. There is no power supply to the electronic engine control unit.
The engine runs intermittently during transients and at idle
1. Leaky air intake system. Check intake system connections. Start the engine and lubricate the contact points and connections in the intake tract with gasoline. If the engine speed increases briefly, repair the leak.
2. Incorrect idle adjustment. Check idle air control, throttle position sensor, lambda control.
3. Full load sensor defective or incorrectly adjusted. Check the throttle sensor.
Hot engine won't start
1. Incorrect adjustment of the CO content. Check CO content and idle speed.
2. Too high pressure in the fuel system. Check fuel pressure, replace pressure regulator if necessary.
3. Clogged or bent return line between pressure regulator and fuel tank. Clean or replace piping.
4. Faulty engine temperature sensor. Check temperature sensor.
5. Leaky power system. Make a visual inspection of all connections in the area of the engine and electric fuel pump. Tighten all connections.
6. Leaky air intake system. Check all intake system connections.
Engine running after shutdown
1. Leaky injectors. Check injectors.
2. On a diesel engine, the fuel cut-off valve does not work.
Lubrication system
The control lamp does not burn after inclusion of ignition
1. Faulty oil pressure sensor. Turn the ignition on, disconnect the wire from the oil pressure sensor and short to «mass». If the lamp lights up, replace the sensor.
2. The sensor is not energized, the contacts are corroded. Check electrical wires and contacts.
3. The control lamp is defective. Replace the control lamp.
4. Faulty control device. Replace control device.
The control lamp does not go out after starting the engine
The oil is overheated. If the control lamp goes out after applying gas, nothing needs to be done.
The control lamp does not go out after applying gas or lights up while driving
1. Oil pressure is too low. Check oil level, top up if necessary. Check oil pressure.
2. The wire to the oil pressure sensor has a short circuit to «mass». Disconnect the cable from the sensor and lay it aside (without closing on «mass»), turn on the ignition. If the lamp lights up, check the wire.
3. The oil pressure sensor is defective. Replace sensor.
Too low oil pressure at all speeds
1. Too little oil in the engine. Add oil.
2. Strainer clogged. Remove the oil pan, clean the strainer.
3. Worn oil pump. Remove the oil pump and check it, replace if necessary.
4. Bearing damage. Remove the engine.
Too low oil pressure at low speeds
Pressure reducing valve stuck open due to contamination. Remove and check the valve.
Oil pressure too high at 2000 rpm
Pressure reducing valve does not open due to contamination. Remove and check the valve.
Cooling system
Overheat
1. Not enough coolant in the system (see chapter Cooling, heating systems).
2. The water pump drive belt is worn or damaged or its tension is not adjusted (see chapters Current service and Engine).
3. The internal channels of the radiator are blocked or dirty (blocked) radiator grille (see chapter Cooling, heating systems).
4. Faulty thermostat (see chapter Cooling, heating systems).
5. Broken or cracked fan blades (see chapter Cooling, heating systems).
6. Faulty fan switch switch.
Attention! When the red-yellow and red-white wires of the sensor are shorted, the fan should run at half speed.
7. Faulty coolant temperature gauge. Check sensor.
8. Faulty water pump. Remove and check the pump.
9. The radiator cap does not hold pressure. Perform a pressure test on the cap.
Hypothermia
1. Faulty thermostat (see chapter Cooling, heating systems).
2. The readings of the temperature meter are inaccurate.
External coolant leaks
1. Damaged or destroyed as a result of aging of the material, the hoses or loosened their fastening on the fittings. Replace hoses and/or tighten hose clamps (see chapter Cooling, heating systems).
2. Damaged water pump seals. In this case, the coolant will seep through the control hole in the pump housing (see chapter Cooling, heating systems).
3. There are leaks from the internal channels of the radiator or side reservoir (ov). The radiator needs to be repaired.
4. There are leaks from the engine drain plug (see chapter Engine) or squeeze plugs of water galleries (see chapter Cooling, heating systems).
Internal coolant leaks
Attention! Internal coolant leaks are usually identified by checking the condition of the engine oil. Inspect the feeler blade and inside surfaces of the cover (lids) cylinders for traces of water and oil foaming.
1. There are leaks at the cylinder head gasket. Perform a pressure test on the cooling system.
2. There are cracks in the cylinder walls or in the head casting. Disassemble the engine to check (see chapter Engine).
Loss of coolant occurs
1. Too much coolant in the system (see chapter Cooling, heating systems).
2. The coolant boils away as a result of engine overheating.
3. There are internal or external coolant leaks.
4. Faulty radiator cap. Check the cover with pressure.
Coolant circulation interrupted
1. The water pump is not functioning properly. The easiest way to verify the operation of the pump is to pinch the upper radiator hose while the engine is idling. If a push of liquid is felt inside the hose when the hose is released, the pump is functioning properly (see chapter Cooling, heating systems).
2. The patency of the cooling system is broken. Drain the coolant, flush the system and refill it with fresh mixture (see chapter Cooling, heating systems). If necessary, remove the radiator (see chapter Cooling, heating systems) and backflush it.
3. The water pump drive belt is worn or damaged or its tension adjustment is broken (see chapters Current service and Engine).
4. Stuck thermostat (see chapter Cooling, heating systems).
Heater
Heater fan not working
1. Fan motor fuse defective. Check fan fuse, replace if necessary.
2. Faulty fan switch. Check if voltage is being applied to the pre-resistors, remove and check the fan switch.
3. Faulty electric motor. Check if voltage is applied to the fan motor terminals with the ignition on and the fan switch closed. If voltage is applied, replace the motor.
The heater fan does not work on one of the stages
Faulty preresistor. Replace connection board.
The heater is not switched off by the regulator
1. Faulty switch. Check switch.
2. Control mixing flap cables are damaged or do not move well. Replace cables.
Heating power too low
1. Coolant level too low. Check coolant level, top up if necessary.
2. The heater control unit has a hard move, is defective. Check the heater control unit, replace the cable if necessary.
Noise in the heater fan area
1. Dirt, leaves got in. Remove the fan and clean it, clean the air channel.
2. Imbalance of the impeller, bearing failure. Remove the fan motor, check for ease of movement.
Automatic transmission (AT)
Attention! Procedures for diagnosing the electronic transmission control system and fault codes are given in the Chapter Engine electrical equipment)
Due to the complexity of the AT design, it is advisable to diagnose its malfunctions and repair components in a car service workshop or a representative office of Mercedes-Benz.
General problems associated with the functioning of the switching mechanism
1. The number of failures associated with a violation of the adjustment of the shift rod includes the following:
- a) The engine can be started in transmission positions other than «R» (parking) And «N» (neutral);
- b) The transmission position indicator reading is different from the actual gear selected;
- c) The vehicle is moving with the transmission in position «R» or «N»;
- d) Transfers are switched with difficulty or arbitrarily.
2. Adjust the shift rod (see chapter Gear box).
Transmission slips, shifts hard, makes strange noises or does not move the car when set to one of the forward or reverse gears
1. There are many possible causes of the problems listed in the title, but only one of them falls under the competence of an amateur mechanic - the wrong level of transmission fluid.
2. Before driving the car to a car service workshop, check the level and condition of the transmission fluid (see chapter Current service). Adjust the level according to the requirements of the Specifications) or change the fluid along with the filter. If the situation does not improve, seek help from specialists.
Transmission fluid leaks
1. AT liquid has a dark red color. Traces of its leaks should not be confused with traces of impellent oil, which can be carried to the transmission crankcase by the oncoming air flow.
2. To identify and locate the source of the leak, first remove all traces of dirt and grease from the transmission boat. Use a suitable degreaser and/or steam clean. Then drive the car for a short trip at low speed (so that traces of the leak are not carried away by the oncoming flow far from its source). Stop, jack up the vehicle and locate the source of the leak by visual inspection. Most often these are:
- a) Transmission oil pan, - tighten the fixing bolts and/or replace the oil pan gasket;
- b) Liquid filling tube, - replace the rubber seal in the place where the tube enters the transmission case;
- c) Transmission fluid lines, - tighten union connections or replace lines;
- d) Ventilation tube - Transmission is overfilled and/or water has entered it.
The oil is brown or smells of burning
Low liquid level in the box (see chapter Current service).
Kickdown mode does not turn on when fully depressing the pedal (no downshift)
1. Low liquid level in the box (see Section Chapters Current service).
2. Malfunction in the engine management system (see Power supply and fuel injection system of a gasoline engine - general information and Diesel fuel injection system - general information Chapters Power and exhaust systems).
3. Malfunction of the sensor or its wiring (see Automatic transmission 722.6 Chapters automatic transmission).
4. Adjustment of a cable of the selector is broken (see Automatic transmission 722.6 Chapters automatic transmission).
The engine does not start in any position of the selector or starts in any position except «R» And «R»
1. The adjustment of the start permission sensor is broken (see Automatic transmission 722.6 Chapters automatic transmission).
2. Malfunction in the engine management system (see Power supply and fuel injection system of a gasoline engine - general information and Diesel fuel injection system - general information Chapters Power and exhaust systems).
3. The adjustment of the selector cable is broken (see Automatic transmission 722.6 Chapters automatic transmission).
Transmission slips, jerks or noises when shifting gears. Vehicle does not move when D or R is engaged
1. Low transmission fluid level (see chapter Current service).
2. Malfunction of the sensor or its wiring (see Automatic transmission 722.6 Chapters automatic transmission).
3. Malfunction in the engine management system (see Power supply and fuel injection system of a gasoline engine - general information and Diesel fuel injection system - general information Chapters Power and exhaust systems).
Bridges
Extraneous noise
1. Ordinary road noise. Not subject to correction.
2. Tire noise. Check the condition of the treads and tire inflation pressure.
3. Worn or damaged wheel bearings or loose torque.
Vibrations
Check the condition of the wheel bearings by alternately jacking the appropriate corner of the car and rotating the wheel manually. Listen for sounds coming from the bearing. Remove the bearings and check their condition.
Oil leaks
Damaged drive shaft seals (see chapter Clutch).
Brake system
Attention! Before concluding that there is a problem with the braking system, check that the tires are in good condition and inflated to the correct pressure, that the front wheel alignment is not out of alignment, and that the vehicle is not loaded unevenly.
Increased brake pedal travel
The brake circuit has failed. Check if brake fluid is leaking.
Brake pedal springs and falls
1. Air in the brake system. Remove air from the system.
2. Not enough liquid in the reservoir. Add new brake fluid, remove air from the system.
3. The formation of steam bubbles. It appears mainly when the brakes are heavily loaded. Change the brake fluid, remove air from the system.
Decreased braking effect, pedal fails
1. Leakage of the pipeline. Tighten tubing connections or replace tubing.
2. Damage to the cuffs in the main or working brake cylinders. Replace cuff. In the main brake cylinder, replace the internal elements, if necessary, replace the main cylinder.
3. Damaged rubber gasket. Repair the caliper.
Poor braking despite high pedal pressure
1. Brake linings are oily. Replace brake pads.
2. Wrong or hardened pads installed. Replace pads. Install original Mercedes-Benz pads.
3. The brake booster is faulty. Check the brake booster.
4. Worn brake pads. Replace brake pads.
Vehicle pulls to one side when braking
1. The tire pressure is not correct. Check and correct tire pressure.
2. Uneven tire wear. Replace worn tires.
3. Brake pads are oily. Replace pads.
4. Different brake pads are installed on the same axle. Replace pads. Install original Mercedes-Benz pads.
5. Poor condition of the brake pads. Replace pads.
6. Contaminated caliper shafts. Clean the guides and seating surfaces of the pads in the caliper.
7. Corrosion of brake caliper cylinders. Replace caliper.
8. Uneven brake pad wear. Replace brake pads (on both wheels).
Spontaneous braking
1. The compensation hole in the main brake cylinder is clogged. Clean the master cylinder and replace the internals.
2. The gap between the drive rod and the master cylinder piston is too small. Check clearance.
Brakes get hot while driving
1. The compensation hole in the main brake cylinder is clogged. Clean the master cylinder and replace the internals.
2. The gap between the drive rod and the master cylinder piston is too small. Check clearance.
3. The throttling hole in the special valve on the bottom is clogged. Clean the main brake cylinder, replace the internal elements and brake fluid.
The brakes are shaking
1. Wrong pads installed. Replace pads, install original Mercedes-Benz pads.
2. The brake disc is corroded in places. Carefully sand the brake disc.
3. The brake disc has lateral runout. Repair or replace the disk.
Brake pads do not move away from the brake disc, the wheel is difficult to turn by hand
Corrosion in brake caliper cylinders. Repair the caliper, possibly replace it.
Uneven pad wear
1. Wrong pads installed. Replace pads, install original Mercedes-Benz pads.
2. The caliper is dirty. Clean out the caliper shaft.
3. Heavy piston stroke. Eliminate.
4. The brake system is leaking. Check the tightness of the brake system.
Wedge-shaped brake pad wear
1. The brake disc does not rotate parallel to the caliper. Check the contact surfaces of the caliper.
2. Corrosion in calipers. Eliminate contamination.
3. The piston is not working properly. Check piston position.
Screeching brakes
1. Often the cause is atmospheric influence (air humidity). If a creak appears after a long stay in high humidity and then disappears, nothing needs to be done.
2. Wrong pads installed. Replace the pads, install genuine Mercedes-Benz pads, coat the base plates with an anti-squeal (anti-squeal) paste.
3. The brake disc does not rotate parallel to the caliper. Check the contact surfaces of the brake caliper.
4. The caliper shaft is dirty. Clean out the caliper shaft.
5. The springs for fastening the pads are bent. Replace mounting springs.
6. Compression springs stretched. Replace compression springs.
Pulsation of the brake pedal
1. ABS in action. OK, no help needed.
2. Too much lateral runout or brake disc thickness tolerance. Check runout and thickness. Repair or replace the disc.
3. The brake disc does not rotate parallel to the caliper. Check the contact surface of the caliper.
The ABS warning light comes on while driving
1. Supply voltage too low (below 10 V). Check voltage. Check if the generator control lamp goes out after starting the engine. If everything is in order, check the alternator drive V-belt.
2. ABS damage. Check for good contact and corrosion at the ground connection on the return pump (in the hydraulic block).
Suspension and steering
Vehicle pulls to one side when moving
1. Tires are unevenly inflated.
2. There is a tire defect.
3. Excessively worn suspension or steering components (see chapter Suspension and steering).
4. Front wheel alignment required.
5. Stuck front brakes (see chapter Brake system).
There are jerks, jerks or vibrations
1. The wheels are out of balance or the discs are oval. Have the tire balanced at a tire shop.
2. Worn wheel bearings, loose torque or out of adjustment (see chapter Suspension and steering).
3. Worn or damaged shock absorbers or other suspension components (see chapter Suspension and steering).
There is excessive rocking of the vehicle/ «burying» his nose when cornering or braking
1. Defective shock absorbers. Replace the whole set (see chapter Suspension and steering).
2. Damaged suspension components. Check the status of the components (see chapter Suspension and steering).
Steering wheel too tight
1. The fluid level in the reservoir of the power steering system has dropped excessively (see chapter Suspension and steering).
2. Tires not properly inflated.
3. Insufficiently lubricated steering gear joints (see chapter Suspension and steering).
4. The adjustment of the angles of installation of the front wheels is broken.
5. The hydraulic booster does not develop the required power.
There is excessive steering play
1. The tightening force of the front wheel bearings has weakened (see chapter Suspension and steering).
2. Excessively worn suspension or steering components (see chapter Suspension and steering).
The power steering system does not develop the proper force
1. The power steering pump drive belt is worn or damaged or its tension is not adjusted (see chapter Suspension and steering).
2. Fluid level too low (see chapter Suspension and steering).
3. The patency of the hoses or lines of the hydraulic system is broken. Check and replace if necessary.
4. Air has entered the hydraulic system. Bleed the system (see chapter Suspension and steering).
Excessive tread wear (not in one area)
1. Tires not properly inflated.
2. The wheels are out of balance. Contact a tire shop.
3. Damaged wheel rims. Check and replace if necessary.
4. Excessively worn suspension or steering components (see chapter Suspension and steering).
Excessive tread wear on outer edge
1. Tires not properly inflated.
2. Too sharp turns are made. Reduce your speed.
3. The adjustment of the angles of installation of the front wheels is broken (excessive convergence). Contact a workshop for professional adjustment.
4. Bent or twisted suspension arm (see chapter Suspension and steering).
Excessive tread wear on the inside edge
1. Tires not properly inflated.
2. The adjustment of the angles of installation of the front wheels is broken (divergence). Carry out the adjustment at a car service workshop.
3. Steering components damaged or loose (see chapter Suspension and steering).
There is localized tread wear
1. The wheels are out of balance.
2. Damaged or bent discs. Check and replace if necessary.
3. There is a tire defect.
Wiper blade defects
Slippage
1. Rubber bands are dirty. Clean the rubber bands with a stiff nylon brush and detergent solution or alcohol.
2. Frayed edges of the brushes, rubber bands worn or torn. Replace rubber bands.
3. Old rubber bands, cracked surfaces. Replace rubber bands.
In the cleaning field, the remaining water immediately collects in drops
The windshield is dirty with lacquer polish or oil. Clean the windshield with a clean cloth with grease, oil, silicone remover.
The brush cleans one-sidedly - one side is good, the other is not
1. The elastic is deformed to one side «no longer tip over». Install new rubber.
2. The wiper arm is twisted, the blade does not fit exactly on the glass. Carefully turn the lever until the vertical position is reached.
Uncleaned surfaces
1. The elastic has come loose from the frame. Carefully insert the elastic into the frame.
2. The brush does not adhere to the glass evenly, as the spring bars or plates are bent. Replace brush. This malfunction first of all appears at careless installation of a spare brush.
3. Lever pressure is too low. Lightly lubricate the wiper arm pivots and springs, or install a new arm.
Tire defects
Heavy tire wear on both sides of the running surface
Tire pressure too low.
Strong tire wear in the middle of the working surface around the entire circumference of the tread
Too high tire pressure.
Uneven tread wear
Static and dynamic wheel imbalance. Perhaps too much lateral runout of the disc, too much play in the bearing joints.
Uneven wear in the middle of the tread
Static wheel imbalance. Possible consequence of a strong vertical beat.
Strong wear of individual sections in the middle of the tread working surface
Traces of blocking at full braking.
Sawtooth tread wear, often along with an invisible tear in the tire's fabric base
Vehicle overload. Check the inside of the tire for warp breaks.
Rubber tabs on the side edges of the tread (scaly wear)
Incorrect wheel alignment. The tire is worn out. Also check the condition of the shock absorbers.
Burr formation on one side of the front wheel tread
Incorrect toe adjustment. The tire is worn out. Frequent movement on undulating surfaces. Fast cornering.
Cord breaks. At first visible only from the inside
Driving over sharp rocks, tire bumps, etc. at high speed.
One-sided wear of the working surface of the tread
1. Check camber adjustment.
2. ABS damage. Check the reliability of the contact of the connection with the body at the return pump (in the hydraulic block).