Invalid Data Received From Body Control Module B
The U0420 code means the vehicle's onboard diagnostic system has detected: Invalid Data Received From Body Control Module B. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $200 - $800 (parts and labor)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
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Common Symptoms
- Rear lighting acting erratically
- Trunk or liftgate controls inconsistent
- Rear wiper operating on its own
- Rear defogger not responding
- Trailer light signals incorrect
Probable Causes (Ranked by Likelihood)
- BCM-B internal failure Very High
- Wiring fault between BCM modules High
- CAN bus interference Moderate
- BCM-B connector water damage Low
Step-by-Step Diagnostic Procedure
-
Scan BCM-B for codes
-
Check wiring between BCM-A and BCM-B
-
Inspect BCM-B connector for water damage
-
Test CAN bus signals
Common Fixes by Vehicle
What techs usually find when diagnosing U0420 on specific vehicles — tap your vehicle for the fix and the exact part:
Most makes (invalid data from a module) moderate DIY
U0420 means a module received implausible data from another control module — often a software/calibration issue or a failing sensor feeding bad values, not a wiring break. Identify which module sets it, check for TSBs/reflashes, and scan all modules for related codes. A full-system bidirectional scanner is essential to pinpoint the source.
Labor: DiagnosticFrequently Asked Questions
Can I drive with U0420?
Yes. Mostly cosmetic and convenience features are affected.
What causes U0420?
Usually BCM-B internal failure or water damage to the module connector.
What is BCM-B?
Larger vehicles often have two body control modules. BCM-B typically handles rear functions.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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