U0136: Lost Communication With Differential Control ModuleRear

U0136 is a network communication fault. It means the vehicle's main CAN bus has stopped receiving messages from the rear differential control module (RDCM). The RDCM manages rear axle torque distribution in AWD and 4WD vehicles, and it communicates constantly with the ECM, ABS module, and stability control system. When that communication drops, the controlling modules can't safely coordinate traction -- the vehicle typically defaults to a conservative or two-wheel-drive fallback mode.

Because U0136 is a communication fault rather than a mechanical one, the actual fault can be in several places. The RDCM itself may have lost power or ground, which would cause it to stop transmitting. A break or corrosion in the CAN high or CAN low wiring between the RDCM and the main bus junction will have the same effect. Less commonly, the module itself has failed. In rare cases, another module on the same CAN network that has gone faulty can corrupt communications across the whole bus and set multiple U-series codes simultaneously -- if you have more than one U code, start with the bus wiring rather than any individual module.

Check the RDCM's power and ground supply fuses and connections first -- it's a fast check and resolves a significant percentage of these faults. If power and ground are good, inspect the CAN wiring harness between the RDCM (typically mounted near the rear differential) and the main under-bonnet or cabin CAN junction for corrosion, connector damage, or rodent damage.