Diagnostics of faults of the petrol injection system (Mercedes-Benz C-Class W202)

Before a fault is found based on fault diagnosis, the following check prerequisites must be met: Start the engine correctly. The following applies to both cold and warm engines: do not press the accelerator pedal when starting, depress the clutch pedal. There must be fuel in the tank, the engine must also be mechanically in order, the battery must be charged, the starter must rotate at a sufficient speed, the ignition system must be in order, the fuel system must be sealed and not contaminated, the crankcase ventilation must be in order, a reliable electrical connection to the vehicle body (engine - gearbox - body) is ensured. Have the fault memory interrogated at a car repair shop.

Caution! If the fuel lines are unscrewed, they must be pre-cleaned using cold cleaning agents (detergents) or gasoline.

Cause	Method of elimination
The engine does not start
When the starter is turned on, the fuel pump with electric drive does not start (no noise is heard during operation)	Lightly tap the pump body to release any possibly stuck pump. Check if there is voltage supplied to the pump. Check electrical contacts for good conductivity.
The fuse is faulty	Check the fuel pump fuse.
Fuel pump relay is faulty	Check the relay.
No voltage supplied to the valve injectors	Remove the plug connectors from the injectors, connect the test lamp and press the starter. The test lamp should blink weakly. If the lamp glows weakly: replace the control device. If the test lamp does not glow: check the fuel pump relay.
A cold engine starts poorly and runs erratically
The temperature sensor is faulty	Check the temperature sensor.
The oxygen sensor is faulty	Have the oxygen sensor checked and replaced if necessary.
The engine stops (works intermittently)
Electrical connections related to the fuel pump intermittently open	Check the plug connections and electrical wire connections on the fuel pump and its relay for a firm and flawless connection. Check the fuse and contact points on the fuel pump relay. Clean the contacts.
Fuel pump delivery too low	Have your auto repair shop check the fuel flow.
The fuel filter is clogged	Replace the fuel filter.
The fuel pump is faulty	Check the fuel pump.
The injector valve is leaking	Check the valve injector.
The engine has defects when operating in transient modes
Air intake system leaking	Check the engine intake system. To do this, leave the engine running in idle mode and lubricate the seals and connections in the intake tract with gasoline. If the rotation speed increases briefly, then the existing leak should be eliminated. Warning: gasoline vapors are poisonous, do not inhale them!
Coolant temperature sensor is faulty	Check the temperature sensor.
The power supply system is leaky	Inspect all connection points in the engine and electric fuel pump area.
Hot engine won't start
Too high pressure in the fuel system	Have the fuel system pressure checked and replace the pressure regulator if necessary.
The drain line between the pressure regulator and the fuel pump is clogged or kinked	Clean or replace the line (pipeline).