There are other faults making a 5 speed Benz automatic transmission going into limp mode. 722.6 transmissions have safety measures so they never fail. Mostly all the time it’s due to a fuse or sensor.

If your Benz isn’t reading the TCM, first make sure it’s not a 90s model or generation hitting the 2000-2001s. Such as a w210 chassis in 2000 still uses the obd 1 and needs a high quality adapter for your scanner to read and delete the codes.

If you use the obd1 port with adapter then it has to be a high quality adapter, I use the autel one with red and black accents. The cheap $10 Chinese ones that are all black can be a hit or miss. I do recall it working one time long ago, but since a few I have purchased have been duds. I’ve went ahead and got a $60 Benz obd1 adapter from Amazon that works well.

If it’s obd2 or obd1 and still not reading the tcm, even using the correct equipment, and the proper scanner, always check the red power wire to the tcm in the plug with 3 wires coming out. The 3 wires are power, ground, signal. With the car on the power wire should have 12v. If it does not check the circuit for any wire damage or blown fuses. If the fuse and wire looks good you can always just add a jumper wire from a powered on 12v connection to the TCM.

For example. Before fixing the fuse in the w211, about fuse 46 or 47, I just jumped the tcm directly from the power distribution block next to the tcm. Started the car and it worked perfectly. That confirmed my suspicion that there was a problem between that connection and the fuse connection. I did check the fuses before which looked good, but over looked the tcm fuse being slightly miss seated as if someone went to take it halfway out.

Wanted to add this video as more clarification for anyone running into this issue. As a quick search I didn’t find much regarding the w211 or Mercedes in general. Most posts are old and vague. This could apply to mostly all Benz. W202, w203, w210, w211, w140, w220, r170, w163, etc