Diagnostics of electrical equipment faults (Mercedes-Benz E-Class W124)

The battery does not hold a charge for long

• Battery failure due to plate shedding.
• The battery terminals are loose or corroded.
• Auxiliary drive belt worn or improperly tensioned.
• The current generated by the generator is not sufficient to fully charge the battery.
• The generator or voltage regulator is faulty.
• A short circuit in the vehicle's electrical circuit, causing the battery to continuously discharge.

The battery charging indicator light is constantly on

• Damage or incorrect tension adjustment of the auxiliary drive belt.
• The generator brushes are dirty, jammed or worn out.
• Damage to the generator brush springs.
• The generator or voltage regulator is faulty.
• Damage to the wiring in the charging circuit.

The battery charge indicator light does not light

• The control lamp has burned out.
• Open circuit in the electrical circuit of the control lamp.
• The generator or voltage regulator is faulty.

The lights are not on

• The incandescent light bulb burned out.
• The fuse has blown.
• The switch is faulty.
• There is a break in the electrical circuit of the light bulb.
• Relay is faulty.
• The contacts in the electrical connector are oxidized.

Inaccurate instrument readings

Instrument readings increase with increasing engine speed

• The voltage regulator is faulty.

Fuel or temperature gauge does not show any readings

• Electrical circuit breakage.
• The sensor is faulty.
• The pointer is faulty.

Fuel or temperature gauge shows maximum value

• Short circuit of an electrical circuit.
• The sensor is faulty.
• The pointer is faulty.

Sound signal malfunction

The sound signal is constantly emitted

• Shorting the horn button to ground or jamming it in the pressed position.
• The horn wire is connected to ground.

The sound signal does not work

• The fuse has blown.
• Broken horn wire.
• The sound signal is faulty.

The sound signal works intermittently

• Horn wire connections are loose or corroded.
• The horn mount is loose.
• The sound signal is faulty.

Windscreen wiper malfunctions

Windscreen wipers do not work or work very slowly

• The windshield wiper blades are stuck on the windshield or the windshield wiper rod is jammed.
• The fuse has blown.
• The contacts in the windshield wiper electrical connector are loose or corroded.
• The windshield wiper relay is faulty.
• The windshield wiper motor is faulty.

Windscreen wiper blades do not completely clean the glass

• The windshield wiper arm is not installed correctly.
• Severe wear of the windshield wiper rod.
• The windshield wiper motor or windshield wiper linkage is loose.

Low glass cleaning efficiency

• The rubber element of the windshield wiper blade is worn out or damaged.
• The windshield wiper arm springs are weak or damaged, or the arm joints are jammed.
• Low concentration of detergent in windshield washer fluid.

Poor performance of windshield washers

Windscreen washer jets not working

• The windshield washer jets are clogged.
• The washer fluid supply hose is disconnected, pinched or clogged.
• There is no fluid in the windshield washer reservoir.

The windshield washer pump is not working

• The contacts in the electrical connector of the washer pump are loose.
• The fuse has blown.
• The windshield washer switch is faulty.
• The windshield washer pump is faulty.

The supply of liquid to the glass occurs some time after the washer is turned on

• The one-way valve located in the hose supplying fluid to the washer jets is faulty.

Poor performance of electric windows

The glass moves in one direction only

• The switch is faulty.

The glass moves very slowly

• The window regulator is damaged.
• Internal door components are interfering with the operation of the window lift.
• The window lift motor is faulty.

The glass does not move

• The fuse has blown.
• The window lift relay is faulty.
• Loose contacts in the electrical connector of the window regulator.
• The window lift motor is faulty.

Poor performance of central locking

The central lock does not work

• The fuse has blown.
• The central locking relay is faulty.
• The contacts in the central locking electrical connector are loose.
• The engine is faulty.

The bolt of the lock moves, but the lock does not open or close

• The switch is faulty.
• The rods or valve lever are damaged or disconnected.
• Relay is faulty.
• The electric motor is faulty. One of the actuators does not work.
• The contacts in the central locking electrical connector are loose.
• The actuator is faulty.
• The valve rods or levers are damaged or disconnected.
• Damage to the valve.