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
Verify the ECM and TCM are receiving proper voltage and have good grounds. p1648-vw
Automatic transmission stuck in a single gear or "limp mode" (shifting harshly). ABS/Traction Control lights on the dashboard. Slow acceleration or poor takeoff performance. Unexplained "no start" conditions. 3. Diagnostic & Troubleshooting Steps
Broken, shorted, or corroded wiring in the powertrain CAN bus network. If water ingress is minor, cleaning the connections
This is a communication error between ECUs, not necessarily a failed sensor. 1. Common Causes
The transmission or braking module itself is failing to communicate. Deep Dive: P1648/18056 – Data Bus Powertrain Malfunction
I can help identify the most likely culprit and direct you to the specific module to check. VW P1648 Code: Troubleshooting and Solutions | JustAnswer