What does it mean?
B2155 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Driver's MPCS Unit Lost Communication with MICU (MICU Message) .
Symptoms
- Seat will not slide forward or backward, or moves only one way
- Memory recall stops partway or does nothing at all
- Positions cannot be stored
- All memory features dead when the message link is the problem, including mirrors and column
- Motor noise without movement, or a grinding sound from the rails
- The code returns each time the seat is moved
Likely causes
- Object trapped under the seat or in the rails blocking the fore and aft travel
- Position sensor inside the horizontal motor worn or failed
- Seat rails dry, dirty or corroded so the motor stalls before reaching the end stop
- Loom under the seat broken by repeated seat travel, the classic failure on this circuit
- Connector under the seat loose, corroded or damp
- Communication line between the seat module and the body module open or shorted
- Low system voltage while several motors run at once
- Memory module internal fault, only after the motor and wiring are proven
How to fix it
- Confirm the manufacturer definition and the correct pins for this application
- Clear the rails, remove trapped items and check the seat slides freely with the motor unplugged
- Watch the horizontal position value in live data across the full travel
- Flex the under seat loom while watching live data, broken strands inside intact insulation are common here
- Inspect and reseat the under seat connectors, checking for green corrosion
- Measure supply, ground and sensor signal at the motor while operating the switch
- Check the communication line for continuity and shorts if the module reports lost communication
- Repair the harness, clean and grease the rails, or replace the motor assembly, then run the seat calibration and verify memory recall