Automatic transmission fault diagnostics (Mercedes-Benz E-Class W124)

Contents: Liquid leaks ↡ If the transmission fluid is brown…↡ Unclear gear selection ↡ Automatic transmission does not…↡ The engine does not start when the…↡

Warning: Because the transmission is a very complex unit, it is difficult to diagnose and repair a fault in the transmission. Do not remove the transmission from the vehicle for repairs until the fault has been professionally identified, as most tests require the transmission to be in the vehicle.

Liquid leaks

The transmission fluid used is usually dark in color, so do not confuse engine oil leaks, which may drip onto the gearbox, with transmission fluid.
To determine the source of the transmission fluid leak, clean the transmission case from dirt using a special agent or steam. Make a test drive for a short distance at low speed so that if there are leaks from the transmission, the air flow does not carry the transmission fluid away from the leak. Raise the car or place it over an inspection pit and determine the leak location. The most likely places for fluid leaks are:

a - oil collector;
b - tube for transmission fluid level dipstick;
c - places of connection of pipes from the heat exchanger.

If the transmission fluid is brown or smells burnt

Gearbox operation with transmission fluid level. In this case, it is necessary to replace the transmission fluid.

Unclear gear selection

Usually, incorrect gear selection is associated with incorrect adjustment of the gear selection cable. Also, unclear gear selection can be associated with other problems:

a - the engine is started not in the PARK or NEUTRAL position of the gear selector lever,
b - the set gear is not displayed correctly on the indicator panel;
c - the vehicle can be driven in the PARK or NEUTRAL position of the gear selector lever;
d - unsystematic gear shifting.