Mercedes-Benz W163 automatic transmission does not upshift
My W163 automatic does not upshift or stays in a low gear, what could be the cause?
A common cause is oil that has got into the transmission plug, which disturbs the control. Cleaning and drying it can restore operation, but the cause of the oil leak must be found. Other causes are the electro-hydraulic control unit inside the transmission and too little oil.
Why does the W163 transmission drop high gears once the car has warmed up?
The transmission control (TCU) drops gears, mostly the higher ones, when it detects excessive heat or slip. It is worth checking first the condition of the plug and whether it is oily, and the amount of transmission oil, before suspecting that the whole transmission is broken.
What prevents the W163 from moving from N into a drive gear?
The cause can be the selector module, or gear lever unit, which has broken. Replacing it may fix the fault. The transmission oil level does not prevent the gear from moving, so oil is not the cause in this case.