How to disassemble the Mercedes 5-speed automatic shifter mechanism

The same shifter mechanism is found in late-model W202 C-Class and some other models, possibly W163 M-Class and W124 E-Class.

The symptoms of a fault with these shifter mechanisms is that the dashboard shows the wrong or no gear, and the car may not start because it does not think it is in park or neutral.

I had a lot of trouble working out how to dismantle the plastic part of the assembly to get access to the electronics, and broke a few parts of it and some clips.

Now that I have it apart, I can provide some instructions that might help someone disassemble their own and hopefully fix it, as a replacement assembly is quite expensive.

See my previous post for how to get access to the assembly, including removing the console:
www.motortraders.net/posts/1788-how-not-to-replace-transmission-shifter-bushing-on-a-mercedes-w202-c-class

Once you have access, remove the four Torx screws that hold the plastic part of the assembly in place. You will then need to disconnect the electrical connection from the top part to the bottom part. On the left side there is a plastic cover that is clipped in place can be levered off with a screwdriver. This will get you access to the connection. Pull out one end - they are clipped in place so you may need to put a screwdriver down one side of the connector to unclip it.

You will also need to disconnect the transmission lock cable which is at the front right of the unit. This rotates anti-clockwise until the key and slot line up and then it just pulls out to the front. Once these are disconnected you can remove the plastic part of the assembly.

To get access to the circuit board, you need to separate part of the unit. It is clipped into place in two places, then it pushes down and out of the other part. See the photo for illustration, but you put a flat screwdriver in the clip at the back and push inwards to unclip, and then the back part can be pushed down. The clip at the front is harder to unclip, but with plenty of prying and pushing mine came out eventually.

Once you get that part out you can then unclip all of the clips to get access to the circuit board. The clips are pretty obvious but look carefully for them as some are outside and some are inside. They are brittle so don't be surprised if you break one or two.

You will then be able to remove the circuit board.

Common problems relate to liquid spills. This may cause the solder to corrode away which can be spotted by seeing exposed copper on soldered connections, possible on electrical components or connectors. This can be fixed by cleaning and resoldering but due to the small surface-mount electrical components, it can be difficult. This was the case with mine, and I cleaned the circuit board with methylated spirits and resoldered a few connections.

For my fault, I also suspected that it could be the gear position switch which is located in the metal part of the shifter mechanism. I had read that these contained light sensors that were activated as the gear lever moved through the different positions.

But when I pulled the switch apart I found it used a variable resistor. These can wear out, but it wasn't a problem with mine.