Mercedes-Benz W203 automatic gear selector and fault code P1856
What do fault code P1856 and the automatic being stuck in one gear mean on a W203?
P1856 means the selector lever position detection is not working. The car usually stays in one gear, for example second, and the gear display is blank or shows the wrong gear. Sometimes only D and N work, and Park cannot be engaged.
What causes a gear selector fault on a W203?
The most common cause is the circuit board of the shifter unit: solder joints or light sensors (opto forks) have come loose, or the electronics are dirty or oily. The wires can also chafe inside the console. If the car moves in Park or does not start, also check the cotter pin on the rod between the shifter and the transmission.
How is a W203 gear selector fault repaired?
Cleaning the unit or repairing the solder joints may help, but the fault often returns. The most common solution is to replace the whole shifter unit, and the part number must match. The centre console has to be removed, and the rear compartment blower motor must be removed first. Fault codes are cleared after the repair.