Mercedes-Benz 400SEL Problems

RepairPal has identified the most common problems with the Mercedes-Benz 400SEL as reported by actual vehicle owners. We'll tell you what the problem is and what it'll take to fix it.

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30
Known Problems

Other than a defective motor, a bad switch or blower motor resistor assembly can cause an inoperative heater blower motor.

A faulty mass air flow (MAF) sensor can cause erratic/rough engine operation and fuel economy issues. Since this sensor measures the actual amount of air entering the motor, when it fails, the engine control module (ECM) takes the wrong information and delivers incorrect volumes of fuel to the cylinders.

A refrigerant leak may develop from one or more of the following AC components: AC compressor, hose manifold for the compressor, or the evaporator core. The loss of refrigerant can cause poor AC performance. Our technicians tell us that proper leak diagnoses should be performed in order to determine the cause of any refrigerant loss.

Ports in the cylinder head related to the emissions air injection and EGR systems can clog; the cylinder head should be removed and the ports cleaned.

Some models have tandem hydraulic pumps—one section for power steering and the other for suspension adjustment. These pumps are prone to leakage from either section.

The lower control arm bushings can wear and crack, resulting excessive movement at the control arm pivot point, leading to irregular and premature tire wear. Worn Ball joints can also cause similar tire wear symptoms. I some cases it may be necessary to replace the lower control arm, including bushings & ball joint to correct this concern.

A cracked or broken heater core outlet housing can cause a coolant leak near the bulkhead (firewall). Our technicians remind us that coolant leaks should be repaired in order to avoid overheating the engine due to coolant loss.

Due to wear, high usage vehicles can experience ignition lock and tumbler failures. The ignition lock cylinder will generally require replacement to correct this concern.

One or more door windows may stop working due to a failed window regulator. Replacement of the failed regulator will be necessary to correct this concern.

Internal and External engine oil & coolant leaks can develop from the head gasket and/or timing cover gasket; these leaks should be repaired before the engine oil and coolant intermix which can result in severe engine damage.

The electronic throttle assembly may suffer an electrical failure. It is often cheaper to send the valve to a service center for repair that to purchase a new part.

Leaks may develop from the differential seals and/or cover on older or high mileage vehicles. Our technicians recommend a complete reseal of the differential unit when these leaks are addressed.

A vibration felt through the center floor of the vehicle can be caused by cracked and/or shredded driveshaft flex discs, resulting in excessive driveshaft movement. If not repaired, damage to the driveshaft center support bearing, transmission, or differential can occur.

The tie rod ends, idler arm, and/or drag link components of the steering linkage may wear prematurely. Please keep in mind the wheel alignment should be checked and adjusted when any of these items are replaced.

A coolant leak may develop form the Radiator due to degradation of its plastic components. Replacement of the failed radiator will be necessary.