Transmissions Services by AR Motorworks Inc.
The newer Mercedes 7-speed transmissions (also called G-tronic) used on many 2004 and newer vehicles have the electronic control unit mounted inside the transmission. These control units are failing frequently with speed sensor codes. The codes usually relate to speed sensor faults.
The speed sensors are not replaceable as they are part of the electrical conductor plate that bolts to the valve body inside the bottom of the transmission. The transmission does not need to be removed to replace the valve body or the conductor plate. A valve body comes complete with the conductor plate / control unit. Early valve bodies must be replaced as a complete unit, but later 2nd, or 3rd generation units can be repaired by just replacing the conductor plate / control unit assembly. We have replaced many of these, and have the capability of performing the SCN coding to complete this repair.
Mercedes-Benz will no longer sell 722.9 valve bodies or conductor plate control units, even with the TRP paperwork completed.
These units are failing so often that the dealer has restricted selling them even in their own shop. To order a part, the dealer must submit a request with computer scans and control unit log reports of the suspected failed vehicle's electronics. The factory then sends the parts they deem necessary for the repair (conductor plate assembly, or complete valve body).
It's rumored that Siemens VDO, the manufacturer of the electrical control units, is in a battle with Mercedes over the validity of failing units. Why should an internal problem with Mercedes and its suppliers affect our ability to acquire parts and repair our customers' vehicles? Mercedes is requiring that the vehicles be brought into one of their dealers for any valve body or conductor plate repair, even if the vehicle is not covered under warranty and the customer is paying for it. In our customers' view this would be perceived as an inability for us to repair their vehicles and give the dealers an unfair advantage at gaining the customers' business. One customer, lost for life to us, could be worth hundreds of thousands of dollars.