If water ingress is minor, cleaning the connections and drying the module can solve the issue, though the water leak (usually clogged sunroof drains) must be fixed.

The Volkswagen fault code is a specific powertrain error indicating a Data Bus Powertrain Malfunction . This code typically means the Engine Control Module (ECM) is not receiving or is receiving corrupted information from another critical module—most commonly the Transmission Control Module (TCM) or ABS module—via the CAN Bus system. Deep Dive: P1648/18056 – Data Bus Powertrain Malfunction VAG Code: 18056

Using a wiring diagram, check continuity of the high and low CAN Bus wires (usually orange/black and orange/brown) between the TCM and ECM. 4. Typical Fixes

Check for accompanying codes like P1626 (missing message from TCM) or ABS/TC-related codes.

Repairing broken CAN bus wires.

Secondary Air Injection System Incorrect Flow Detected. P1648. 18056. Data Bus Powertrain Malfunction. Customer. JustAnswer Jeep Grand Cherokee Diesel P0700 P1648 Codes Explained

Pull up the passenger-side carpet/sill panel, open the TCM plastic box, and look for water, condensation, or green corrosion on the pins.

The transmission or braking module itself is failing to communicate.