W211 E220 CDI OM646 Limp Mode

[fafaza]

My car went into limp mode. The car refuses to change gears, and when switching to the “drive”, “park” or “reverse” driving mode, the car jerks sharply. I am getting a P0720 powertrain output speed sensor fault code and a P23C1 powertrain fault code. The dashboard shows ABS and ESP faults but I'm not sure if they are correct as my OBD2 scanner is a phone app and it's not very good. I searched long and hard for the cause, but got headaches and varied results, from the transmission module, solenoids, transmission speed sensors, and wheel speed sensors (mag rings), to a rusty ABS ground wire, and even a faulty throttle body. I don't even know where to start. I changed the gearbox oil before winter, everything wasn't that bad. I changed the rear ABS sensor, and then I saw that the magnetic ring was counting down its last days. Could this be the reason for the limp mode? Then ABS and ESP errors appeared on the dashboard, I drove for about a week without any problems, and then the car got stuck in 1st gear, I restarted the engine and everything was fine until the next engine start, after that nothing could get it out of limp mode. I would also like to find the throttle body to clean. It showed an open error on various OBD2 scanners. The engine is OM646.821, a diagram of the part access would be very helpful. I have attached a photo of the engine just for reference.

 

[Mersovod]

1. Please provide VIN for accurate identification of the electrical circuit.
2. According to EGS, such cases usually require replacement of the board.

 

[keimonen]

You didn't mention what transmission the car has or what year it is? As mentioned, it could be the TCM, but at least the early 7G transmissions also had a fairly common solenoid issue.

 

[fafaza]

So quick update, new scan showed fault codes for both rear circlips (mag rings) and same transmission and more fault codes, after cleaning and rechecking and with wheel speed sensor readings, wheel spin gave no reading on right side, left side sometimes gave readings and sometimes not, changed the ring and limp home mode is gone. Transmission runs like new. Still getting lots of errors though, going to buy and try the left circlip. I think it was just ABS issues and since I drove long distances with the error it just locked the transmission to keep it safe.

 

[fafaza]

Update, so apparently it was indeed both rear ABS rings, replaced and problem solved, shifts almost like new. The other SRS fault light just came on and went out, I'm thinking that was related and should stop coming on, just the modules still confused? Well that's a fight for another time and I guess another thread if I can't figure it out myself or go through the search. Thanks for trying to help

 

[dicsun]

You also need to reset the gearbox adaptation as it is now out of order.