W211 fault code 740, urgent help needed.
 

The CDI keeps giving a 740 error code, torque converter circuit solenoid issue. I tried to clear it but the check engine light flickers and the same fault comes back. Basically I cannot clear it. The car runs fine and shifts ok. It happens this morning and it is driven locally only with no issues, not at freeway speed. I suspect it is the conductor plate which was replaced 30k miles ago. What puzzle me is that I can't clear the code. Any thoughts? It is a 722.6 transmission. Thanks.

What are you using to clear the code?

ODB2.

Not sure which code reader you have but you will need to be able to communicate with transmission.

Problem solved, I hope. I used the ICarsoft tool to read the TCM code. It shows 5 stored codes P2560, p229a, p2561, p2511, p2602. I cleared them all then I can clear the odb code 740. Took it out for a test drive, for a 10 miles freeway trip and all is well. Read code in the TCM again and no code. Hope it is a random thing but will research the 5 codes.

I would be looking to change out the conductor plate. You probably have an internal speed sensor that is failing.

Also do the 13 pin plug for good measure. Actually that is a thought. Inspect the wiring harness coming out the transmission and look at the transmission controller end and make sure fluid hasn't wicked up the wires and is shorting out the transmission controller.

At least on the 722.6 that is DIY. On the 2007-2009 W211s that have 722.9 transmissions that is a dealer only operation due to the integrated transmission controller inside the conductor plate. They will not sell you the conductor plate at the parts counter because it is a "Theft Relevant Part" and also needs version coding with legit Xentry that can phone back to Germany to get the encryption keys for your vehicle based on the VIN. It's about a $2k operation at the dealer including the requisite transmission service that will be done as a part of this.