722.6 Common issue you need to check for!

The Mercedes 722.6 transmission is no stranger to problems. One of the common components of the system to fail is actually outside of the transmission and is often overlooked until it is too late. If you don’t already know, we are talking about the EGS52, or transmission control module (TCM). Often mounted in the module case of the engine bay or passenger side footwell, they commonly fail due to transmission fluid wicking up the harness over time and into the unit case due to leaking pass-through connector o-rings at transmission.

If your vehicle has erratic or harsh shifts, and a multitude of trouble codes are stored in the TCM, check the electrical connector on the front LH side of the transmission for signs of oil intrusion as pictured.

The harness connects to the conductor plate through the pilot bushing. The pilot bushing has two O-rings which are meant to protect the electrical connection from the oil. These O-rings may leak causing oil to fill the connector cavity and travel through the wiring harness up to the TCM.

If oil is found inside the harness at the TCM connection, remove the module from its plastic housing. Carefully clean the module with an appropriate electrical contact cleaner and dry it thoroughly.

Reassemble the vehicle, clear the trouble codes and perform a road test. If the problem persists, it’s possible that the TCM was damaged by the oil intrusion.