If you have the similar issue as the following parts described, wish the working solution advised by experienced technicians will help you.
Car model and miles:
2007 Mercedes Benz S550, Car gas approx 110k miles and I just purchased it about 2 months ago.
Diagnostic tool to use:
MB star diagnostic tool SDCONNECT C4.
Look at this one, on sale at present $499 with WIFI:
I was driving to dinner on night and car felt like it was pinging on the freeway, it did it a few times but eventually made it home safe. Leaned towards it not being an engine issue because car revs fine in neutral or park.
Next day, I was leaving the mall when all of a sudden the car goes into “limp mode” I was stuck in the parking lot because car would not go into any gear. When I put it into R or D it would just rev up and not move at all. Eventualy it would not even rev up even after pressing the gas.
I was able to make it home by power cycling the car (turn off, open/close door, activate alarm, and then restart). After power cycling the car would shift fine for a few seconds and then go into “limp” mode again. I noticed it would usually happen after getting into about 3rd gear.
I go to start it about a week later and car goes into d/p fine when cold, but same thing after a while, limp mode.
When I first start car up and rev in neutral or park it sounds fine, but after a while when I rev in p/n it has a weird winding noise (electric motor is sound, high pitch). When I power cycle and rev again noise goes away. It also gave me a random P0653 High Voltage Code, but I think this may not be relavant or random, I don’t know. Voltage seems fine after scanning with my scanner (between 13.5-14.5V).
Working solution advised by experienced technicians:
If you place it on the Diagnostic Assistance System (DAS built in MB star) you will have the answer within 2 minutes start-to-finish on the Quick Test. Until then, you’re just throwing time, parts, and money at it in the hope you’ll hit the target (in the dark while wearing a blindfold).
On the 722.6 transmission, there are 65 diagnostic failure codes. I will assume it is similar on yours.
An OBD2 code reader helps but is not optimal. Example, one OBD code (P0700) is displayed for eight unique diagnostic trouble codes (DTC 041 through 052).
The info on the transmission error codes is out there but you’ll have to spend some time searching for it.
These are complicated cars and some tests require specialized equipment. You either buy it or you pay someone who has it. You can always post a request to see if someone in your area has the diagnostic system and is willing to come over to your place. Otherwise, flat-bed the car to a shop with the tools.