Electrical system faults (Mercedes-Benz C-Class W201)

Note: Solutions to problems related to the starting system are described above - in the list called "Engine" in this section.

The battery runs out in a few days

• Internal battery failure (Chapter 5A).
• The battery terminal clamps are loose or oxidized ("Weekly check").
• Worn or slipping alternator drive belt (Chapter 1).
• Low Generator Charging Current (Chapter 5A).
• The generator or voltage regulator is faulty (Chapter 5A).
• Short circuit causing battery discharge (Chapters 5 and 12).

Low battery warning light stays on when engine is running

• Worn or slipping alternator drive belt (Chapter 1).
• Worn, stuck or dirty generator brushes (Chapter 5A).
• The generator brush springs are broken or weakened (Chapter 5A).
• Internal fault in the generator or voltage regulator (Chapter 5A).
• Open, disconnected or loose contacts in the charging circuit (Chapter 5A).

The low battery indicator light does not turn on

• The signal lamp burned out ("Weekly check").
• Open, disconnected or loose contacts in the control lamp circuit (Chapter 12).
• Generator faulty (Chapter 5A).

The lighting fixtures are not working

• The lamp burned out (Chapter 12).
• Corrosion of the contacts of the bulb socket (Chapter 12).
• The fuse has blown (Chapter 12).
• Turntable malfunction (Chapter 12).
• Break, disconnection or weakening of contact in the circuit (Chapter 12).
• The switch is faulty (Chapter 12).

Instrument readings are inaccurate or erratic

Instrument readings increase with increasing engine speed

• The voltage regulator is faulty (Chapter 12).

Fuel level and temperature gauges do not function

• The pointer sensor is faulty (Chapters 3 and 4).
• The wiring circuit is open (Chapter 12).
• The indicator is faulty (Chapter 12).

Fuel level and temperature gauges constantly show maximum values

• The pointer sensor is faulty (Chapters 3 and 4).
• Short circuit in electrical wiring (Chapter 12).
• The pointer is faulty (Chapter 12).

The sound signal does not work or works poorly

The sound signal does not turn off

• Shorting of the horn contacts or sticking of the horn button
• Closing the contact of the sound signal button to the housing (Chapter 12)

The sound signal does not work

• The fuse has blown (Chapter 12).
• The steering wheel wiring is broken or has a poor connection (Chapter 12).
• The sound signal is faulty (Chapter 12).

The sound signal emits a pulsating sound (unstable) or unsatisfactory sound

• Poor contact of electrical wires (Chapter 12).
• The horn mount has become loose (Chapter 12).
• Faulty sound signal (Chapter 12)

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Windscreen wipers do not work or work poorly

Windscreen wipers do not work or work very slowly

• Wiper blades sticking to the glass or the linkage jamming (Chapter 12).
• The fuse has blown (Chapter 12).
• Electrical wiring is broken or disconnected (Chapter 12).
• Relay faulty (Chapter 12).
• The windshield wiper motor is faulty (Chapter 12).

The wiper blades are moving over too large or too small an area of the glass

• The wiper arms are not correctly positioned on the axles (Chapter 12).
• Excessive wear of the wiper linkage (Chapter 12).
• The windshield wiper motor or linkage has become loose (Chapter 12).

Windscreen wipers are not working effectively

• The rubber pads of the windshield wipers are worn out or damaged ("Weekly check").
• The windshield wiper arm pressure springs are broken or the swing arm hinges are jammed (Chapter 12).
• The content of cleaning additive in the washer fluid is insufficient for effective glass cleaning ("Weekly check").

Windscreen washers do not work or work poorly

One or more washer nozzles are not working

• Contamination of holes (Chapter 1).
• Disconnection or kinking of the hose (Chapter 12).
• Not enough fluid in the washer reservoir ("Weekly check").

The washer pump does not work

• The pump wiring connection is broken (Chapter 12).
• The fuse has blown (Chapter 12).
• The washer switch is faulty (Chapter 12).
• The washer pump is faulty (Chapter 12).

The washer pump runs for some time before the fluid starts to flow

• The pressure valve in the washer hose is faulty (Chapter 12).

The electric window does not work or works poorly

The glass moves in one direction only

• Faulty switch (Chapter 12).

The glass moves slowly

• Damage, sticking or lack of lubrication of the regulator (Chapter 11)
• Contamination of the regulator or internal components of the door (Chapter 11)
• Faulty engine (Chapter 11).

The glass won't move

• The fuse has blown (Chapter 12).
• Relay faulty (Chapter 12).
• The engine wiring is damaged (Chapter 12).
• Faulty engine (Chapter 11).

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The central lock does not work or works poorly

The system is completely inoperative

• The fuse has blown (Chapter 12).
• Relay faulty (Chapter 12).
• The electrical wiring is broken (Chapter 12).
• Electric motor failure (Chapter 11).

Locks close but do not open or open but do not close

• The main switch is faulty (Chapter 12).
• The levers or rods of the lock lever transmission are broken or disconnected (Chapter 11).
• Relay faulty (Chapter 12).
• Electric motor failure (Chapter 11).

The electromagnetic relay/motor of one of the locks does not work

• The electrical wiring is broken (Chapter 12).
• The lock motor is faulty (Chapter 11).
• The levers or rods of the lock lever transmission are broken or disconnected (Chapter 11).
• Door lock fault (Chapter 11).