Pull up the passenger-side carpet/sill panel, open the TCM plastic box, and look for water, condensation, or green corrosion on the pins.
If internal module damage is diagnosed. If you can provide: The exact vehicle year and model (e.g., 2004 Passat 1.8T). Any other fault codes (e.g., P1626, ABS codes). If the ABS or Transmission light is on.
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.
Repairing broken CAN bus wires.
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
Secondary Air Injection System Incorrect Flow Detected. P1648. 18056. Data Bus Powertrain Malfunction. Customer. JustAnswer Jeep Grand Cherokee Diesel P0700 P1648 Codes Explained
