What it means
Other modules receive implausible body status data (e.g. all doors reported closed while ajar). Comfort and lighting features can behave inconsistently.
How it works
The body control module (BCM) broadcasts status such as door and lighting states over the vehicle network. Other modules check whether BCM A's messages are valid and consistent; U0431 sets when a receiving module rejects that data as implausible. A software mismatch, routing problem, or CAN network fault can corrupt or misdirect otherwise useful status messages.
Common causes
Most likely first.
- BCM software version mismatch
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and record U0431, related communication codes, and freeze-frame details to identify which module rejected BCM A's data and when.
- Compare live BCM A door, ajar, and lighting status with the actual vehicle state to see which reported values are implausible.
- Inspect BCM A and gateway connectors, grounds, power supply, and CAN wiring for looseness, corrosion, damage, or poor repairs.
- Check whether the BCM or gateway was recently replaced or updated, and verify module software compatibility for the vehicle.
- Test CAN network continuity and termination resistance using the manufacturer's procedure and specification, then investigate gateway routing if the wiring checks out.
Common fixes
- Repair a loose, corroded, or damaged BCM A or gateway connector.
- Repair damaged CAN wiring or a poor ground affecting BCM A communications.
- Correct incompatible BCM or gateway software with the appropriate vehicle configuration.
- Repair or replace a faulty gateway or CAN termination component after network tests confirm the fault.
Can I keep driving?
If door, lighting, or other body functions are unreliable, avoid relying on affected features and check that doors and lamps work before driving. Multiple warning lights or disabled functions can indicate broader network problems; arrange diagnosis soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.