Q: Car will not shift into reverse or park.

Hi, thanks for writing in. Try turning the car off then shifting it to park. If that works, most likely the causes are the brake light switch or the transmission control module. From previous experience working in a Mercedes service department, those are the two most likely causes. The brake light switch can have an internal short. It is the first link in the chain, so to speak. The brake light switch not only signals the brake lights, it also tells the ABS computer you have your foot on the brake pedal and also tells the transmission control module the same thing. The transmission control module may also have and internal short. Also, there has been cases where transmission fluid migrated within the wiring harness up into the transmission control module, causing similar issues. I suggest the car be checked by a technician to verify which is the issue as replacing parts in a Mercedes can get quite costly. It’s best to have a technician verify things first. Here at YourMechanic, we can have a technician come to your home or office to inspect and diagnose this issue for you, and make or suggest the necessary repairs.