Engine malfunctions (Mercedes-Benz C-Class W201)

Engine does not turn over when trying to start

• The battery contacts are loose or oxidized ("Weekly check").
• The battery is discharged or defective (Chapter 5A).
• Faults in the starter circuit wiring (Chapter 5A).
• The traction relay or starter switch is faulty (Chapter 5A).
• Starter faulty (Chapter 5A).
• The starter gear or flywheel ring gear teeth are loose or broken (Chapter 5A).
• The engine grounding is broken (Chapter 5A).

The engine turns but does not start

• Empty fuel tank.
• The battery is discharged (the starter turns slowly) (Chapter 5A).
• The battery contacts are loose or oxidized ("Weekly check").
• Ignition system components are damp or damaged - petrol engines (Chapters 1 and 5).
• The wiring in the ignition circuit is damaged - gasoline models (Chapters 1 and 5).
• Worn, faulty or incorrectly gapped spark plugs - petrol engines (Chapter 1A).
• Heating system malfunction - diesel models (Chapter 5G).
• Choke or carburetor failure - petrol carburetor models (Chapter 4A)
• Shut-off valve failure - petrol carburetor models (Chapter 4A).
• Fuel injection system malfunction - petrol models with fuel injection (Chapter 4B)
• Stop Valve Malfunction - Diesel Models (Chapter 4B).
• Air in the Fuel System - Diesel Models (Chapter 4B)
• Serious mechanical failure (for example, a broken camshaft drive belt) (Chapter 2).

The engine does not start when cold

• Battery is low (Chapter 5A).
• The battery contacts are loose or oxidized ("Weekly check").
• Worn, faulty or incorrectly gapped spark plugs - petrol models (Chapter 1A).
• Heating system malfunction - diesel models (Chapter 5G).
• Choke or carburetor failure - petrol carburetor models (Chapter 4A).
• Fuel injection system malfunction - petrol models with fuel injection (Chapter 4B).
• Another malfunction of the ignition system - gasoline models (Chapters 1 and 5).
• Incorrect High Idle Speed Valve Adjustment - Diesel Models (Chapter 4B).
• Low compression in engine cylinders (Chapter 2).

The engine does not start when hot

• The air filter element is dirty or clogged (Chapter 1).
• Choke or carburetor failure - petrol carburetor models (Chapter 4A)
• Fuel injection system malfunction - petrol models with fuel injection (Chapters 4B).
• Low compression in engine cylinders (Chapter 2).

Excessive noise when starting the starter

• The electric starter gear or flywheel ring gear teeth are loose or broken (Chapter 5A).
• Loosening the starter mounting bolts (Chapter 5A).
• The internal components of the starter are worn or damaged (Chapter 5A).

The engine starts and immediately stalls

• Open or loose contacts in the ignition circuit (Chapters 1 and 5).
• Air leakage into the carburetor, throttle chamber or intake manifold - petrol models (Chapters 4).
• Carburetor malfunction (clogging of jets and internal channels) — gasoline carburetor models (Chapter 4A).
• Fuel injection system malfunction - fuel injected models (Chapter 4B).

The engine runs rough at idle

• The air filter element is dirty or clogged (Chapter 1).
• Air leak in the carburetor, throttle chamber, intake manifold or associated hoses - gasoline models (Chapter 4A).
• Spark plugs are worn, faulty or incorrectly gapped - petrol models (Chapter 1A).
• Uneven or low compression in engine cylinders (Chapter 2).
• Camshaft cam wear (Chapter 2).
• Incorrect installation of the camshaft drive chain (Chapter 2).
• Carburetor malfunction (clogging of jets and internal channels) — carburetor models (Chapter 4A).
• Fuel injection system malfunction - fuel injected models (Chapters 4B).
• The fuel injectors are faulty

Misfiring when engine is idling

• Spark plugs are worn, faulty or incorrectly gapped - petrol models (Chapter 1A).
• The spark plug high voltage wires are faulty (Chapter 1A).
• Air leak in the carburetor, throttle chamber, intake manifold or associated hoses - gasoline models (Chapters 4A).
• Carburetor malfunction (clogging of jets and internal channels) — gasoline carburetor models (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).
• Injector failure - diesel models (Chapter 4B).
• Crack in distributor cap or internal failure - petrol models (Chapter 5).
• Uneven or low compression in engine cylinders (Chapter 2).
• Rupture, leak or kink in the engine crankcase ventilation hose (Chapter 4).

Engine ignition failures at operating speeds

• The fuel filter is clogged (Chapter 1).
• The fuel pump is faulty or the fuel supply pressure is low (Chapter 4).
• The fuel tank ventilation system or fuel line is clogged (Chapter 4).
• Air leakage into the carburetor, throttle chamber, intake manifold or associated hoses (Chapter 4A).
• Spark plugs are worn, faulty, or the spark plug gap is incorrect (Chapter 1A).
• Spark plug high voltage wires are faulty - petrol models (Chapter 1A).
• Fuel Injector Failure - Diesel Models (Chapter 4B).
• Crack in the distributor cap or internal breakdown (Chapter 5).
• Ignition Coil Malfunction - Petrol Models (Chapter 5).
• Uneven or low compression in engine cylinders (Chapter 2).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).

The engine accelerates slowly

• Spark plugs are worn, faulty, or have incorrect gap (Chapter 1).
• Air leakage into the carburetor, throttle chamber, intake manifold or associated hoses (Chapter 4).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapters 4B or 4B).
• Fuel Injector Failure - Diesel Engines (Chapter 4B).

The engine stalls

• Air leaks into the carburetor, throttle chamber, intake manifold or associated hoses (Chapter 4A).
• The fuel filter is clogged (Chapter 1).
• The fuel pump is faulty (Chapter 4).
• The fuel tank ventilation system or fuel line is clogged (Chapter 4).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).
• Fuel Injector Failure - Diesel Engines (Chapter 4B).

The engine does not develop power

• Incorrect installation of the camshaft drive chain (Chapter 2).
• The fuel filter is clogged (Chapter 1).
• Fuel pump defective or low fuel pressure - petrol models (Chapter 4).
• Uneven or low compression in engine cylinders (Chapter 2).
• Spark plugs are worn, faulty, or have incorrect gap (Chapter 1A).
• Air leakage into the carburetor, throttle chamber, intake manifold or associated hoses (Chapter 4A).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).
• Fuel Injector Failure - Diesel Models (Chapter 4B).
• Incorrect injection pump timing - diesel models (Chapter 48).
• Brakes sticking (Chapters 1 and 9).
• Clutch slippage (Chapter 6).

Backfires in the engine

• Incorrect installation of the camshaft drive target (Chapter 2).
• Air leakage into the carburetor, throttle chamber, intake manifold or associated hoses (Chapters 4A).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).

When starting the engine, the low oil pressure warning light comes on

• Low oil level or wrong oil type ("Weekly checks").
• The oil pressure sensor is faulty (Chapter 5).
• Engine bearings and/or oil pump are worn out (Chapter 2).
• Engine overheating (Chapter 3).
• The oil pressure reducing valve is faulty (Chapter 2).
• The mesh filter of the intake pipe is clogged (Chapter 2).

The engine continues to rotate after being turned off

• Excessive contamination of engine pistons (Chapter 2).
• Engine overheating (Chapter 3).
• Fuel shut-off valve faulty - petrol carburetor models (Chapter 4A).
• Fuel injection system malfunction (Chapter 4B).
• Stop Valve Malfunction - Diesel Models (Chapter 4B).

Noises when the engine is running

Pre-ignition (detonation) or knocking when accelerating or under load

• Incorrect ignition setting/ignition system malfunction - petrol models (Chapters 1 and 5A).
• Incorrect selection of spark plugs (Chapter 1).
• Wrong type of fuel.
• Air leaks in the carburetor, throttle chamber, intake manifold and associated hoses (Chapter 4A).
• Excessive contamination of engine pistons (Chapter 2).
• Carburetor malfunction (clogging of jets and internal channels) (Chapter 4A).
• Fuel injection system malfunction (Chapters 4B or 4B).

Whistling or wheezing noises

• Leaking intake manifold or carburetor/throttle body gasket (Chapter 4A).
• Leak through the exhaust manifold gasket or through the exhaust pipe connection to the manifold (Chapter 4).
• Leak in vacuum hose.
• Cylinder head gasket failure (Chapter 2).

Knocking or rattling noises

• Worn valve train or camshaft (Chapter 2).
• Malfunction in auxiliary units (cooling system pump, generator, etc.) (Chapters 3 and 5 etc.).

Knocks or thuds

• The lower connecting rod head bearings are worn out (regular strong impacts, possibly less under load) (Chapter 2).
• The main bearings are worn out (rumble and impact, possibly increasing under load) (Chapter 2).
• Piston relocation (can be heard on a cold engine) (Chapter 2).
• Malfunction in auxiliary units (cooling system pump, generator, etc.) (Chapters 3 and 5 etc.).