01 Pressed the Gas, But Going Nowhere? Why Your Car Won't Acce… • 02 The Heart of Automatic Transmissions: A Closer Look at Torq… • 03 Why Mechanics Don’t Always Show You the Real Fault • 04 Never Test an Alternator by Disconnecting The Battery. Here… • 05 People Left Horrified After Discovering Why Airbags Sometim… • 06 Fix That Check Engine Light Today: 5 Simple Sensor Cleaning… • 07 Front Tires vs. Rear Tires: Where Do New Ones Belong? Exper… • 08 The Most Problematic Mitsubishi Cars: A Comprehensive Review • 09 The Hidden Cause of Poor Fuel Economy After Basic Repairs • 10 The Hidden Reason Engines Struggle To Idle Smoothly Before … •

DTC codes / Volkswagen codes / P1855

P1855 · VolkswagenCAN Bus Software Version Control

P1855 on Volkswagen vehicles indicates that the controller area network (CAN) bus software version stored in one or more control modules does not match the version expected by the gateway or another module on the network. The computer detected a mismatch in the software version identifier exchanged during CAN bus communication, which can prevent proper coordination between modules.

SystemPowertrain
Code typeVolkswagen specific
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Malfunction indicator lamp (MIL) illuminated on the dashboard
  • Often no symptoms besides the warning light
  • Multiple unrelated warning lights or messages on the instrument cluster
  • Intermittent communication faults or modules dropping offline
  • Reduced functionality of convenience systems such as central locking or windows
  • Engine may run normally or exhibit minor drivability issues if communication is disrupted

Common causes, most likely first

  1. Control module software not updated after a replacement or reprogramming procedure
  2. Incorrect software version flashed into a module during a previous repair
  3. CAN gateway module firmware mismatch with other network participants
  4. Aftermarket or non-OEM module installed with incompatible software
  5. Corrupted software in a control module due to voltage spikes or programming errors
  6. Wiring or connector issues causing intermittent CAN bus communication that triggers version checks
  7. Failed or failing control module affecting software version reporting

How to diagnose and fix it

  1. Connect a Volkswagen-compatible scan tool and read all module fault codes to identify which modules are involved
  2. Check the CAN gateway installation list and compare software versions across modules
  3. Verify battery voltage and perform a full vehicle scan to rule out low-voltage communication glitches
  4. Inspect CAN bus wiring and connectors for damage or corrosion, especially at the gateway and affected modules
  5. Reprogram or update the affected control module software using the manufacturer's diagnostic equipment
  6. Replace any aftermarket module with a correct OEM unit and perform coding and adaptation
  7. Clear fault codes and perform a road test to confirm the mismatch is resolved

Software mismatch traps on Volkswagen CAN networks

  • A common cause is a replacement module from a different model year or trim that physically fits but carries incompatible software, so always verify part numbers and software versions before installation.
  • This code often appears after a battery replacement or jump-start if voltage dropped during a module's self-check, and it may clear after a proper drive cycle if no permanent mismatch exists.
  • Technicians sometimes replace the gateway module unnecessarily when the real fault is a single module with outdated software that keeps broadcasting an old version identifier.
  • Intermittent CAN bus faults from chafed wiring can cause sporadic version mismatches that mimic software problems, so always inspect wiring before flashing modules.
  • P1855 does not always mean a module is defective; it can be a stored history code from a previous repair that was never cleared after programming.

Can I keep driving with P1855?

The vehicle is generally safe to drive if it runs normally and only the warning light is on, but avoid long trips or towing until the fault is diagnosed. If multiple warning lights appear or the engine runs poorly, have the vehicle inspected promptly because communication issues can affect safety systems.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage