A rough running motor or lack of power can be caused by a failed distributor cap or rotor, ignition wires (or their resistors), or valve cover gasket leaks. If the valve cover gasket leaks, oil can pool where the ignition wire resistor connects to the spark plug. The resistor can fail and the spark plug may not fire because of a short circuit through the oil.
Mercedes-Benz 420SEL Problem Reports
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Other than a defective motor, a bad switch or blower motor resistor assembly can cause an inoperative heater blower motor.
The fuel pump and/or fuel pump relay can fail, causing the car to crank over but not start. Proper diagnoses will be necessary to confirm if the pump or relay is at fault.
The climate control system can fail or perform erratically due to internal problems with the climate control button electrical contacts. Replacement of the climate control assembly is commonly required to correct this problem.
A refrigerant leak may develop from one or more of the AC hoses. Proper leak detection procedures should be followed if refrigerant loss in encountered. Replacement of any leaking hoses will we required to restore proper AC operation.
It is not uncommon for the idle air compensator to get stuck in one position, resulting in the engine idle speed (rpm) being too high or too low. Replacement of the failed compensator may be necessary to correct this concern.
Valve stem seals may wear and cause the engine to burn oil. this can contaminate the catalytic converter and cause it to fail.
High mileage vehicles may develop a transmission fluid leak from one or more of the oil seals.
A worn steering dampening shock can cause a fluid leak at the front of the vehicle. If a leak is noted from the dampening shock, our technicians tell us that it should be replaced.
The instrument cluster, along with the turn signal and wiper combination switch, can fail.
As brake fluid becomes dirty over time, it can cause a failure of the anti-lock brake system (ABS) modulator assembly. Our technicians recommend a complete brake system flush every two years to help prevent this issue.
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.
One or more blend door vacuum actuators may fail resulting in the incorrect output temperature from the HVAC system. Failed actuators will require replacement to restore proper HVAC operation.
The brakes may begin to squeak at about the 50 percent wear point. This is due to the size and material used for the brake pads and rotors. The brake rotor surfaces become uneven, causing a lip to form at the outer edge. This will generally require replacement of the rotors when the pads are worn (pad life varies depending on driving style and terrain).
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.