Repair-It

Several times now the car has not responded to pushing the park button. This appears to be a common issue. I wonder if I should consider replacing the shifter assembly if this is the cause and it's not too expensive. I haven't read the whole thread yet.

https://mbworld.org/forums/w212-amg/867 ... rking.html

Ah - looks like they had some limited/weak solder stuff going on too.

You need to isolate issues with the button itself (usually the victim of a previous liquid spill), or the ISM which is usually bolted to the transmission. Neither a brand new shifter assembly nor an ISM will be cheap. You may have some luck with an intermittent park button but the ISM isn't really repairable. I don't know if the ISM (or shifter) has security features making replacement more annoying (used or new).

With the dual clutch I don't know if the ISM is the same or not (722.9 ISMs are made by Continental). See if opening the door would normally force park mode (either try it or read the manual). If you believe this to be a design function on your 2015 (I don't know), then try opening the door next time. If it responds when the park button doesn't, then it's the button in the shifter assembly. If still nothing, it's the ISM (or whatever the equivalent is) on the side of the transmission.

On the 722.9, the ISM has a number of cycles counter and aside from actually failing they can also trip that counter which would present "drive to workshop" type messages on the display. That doesn't sound like your issue.

A full code scan may shed some additional light. If there are no codes at all it's more likely to be a failing button from a previous liquid spill which is probably the most desirable problem to have all things considered.

The web forum said that shifter signal issues were common. Other data points are that each time it has gone into park with either opening the door or shutting off the ignition, which makes me think it's a control signal problem.

So you think it's a shifter module issue but not the park button?

I would expect but cannot guarantee strange fault codes in that module if it's really misbehaving. As I said before a crudded-up park switch will not have a code because it's a mechanical system. You can also use a scan tool to test the park button.

I guess I meant park button "signal". The interweb forum post talked about bad solder joints on the PCB for the shifter that includes the "dual" park switch.

I would be inclined to expect some sort of "invalid data received from ____" type codes for garbage on the network. Or even some kind of internal fault code.

I don't know that you have enough information to conclude that there is a bad solder joint internally as the root cause.