What it means
A receiving module detected implausible data from rear lighting control module A. Tail/brake/turn/reverse lamp command vs. feedback values fail plausibility checks and are rejected.
How it works
Rear lighting control module A reports commands and feedback for rear lamps such as tail, brake, turn, or reverse lights. A receiving module sets U0484 when the rear lighting command and feedback data is implausible and rejected.
Common causes
Most likely first.
- Module internal fault or sensor input drift
- Software version mismatch after replacement
- Gateway module routing CAN messages incorrectly
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 the body and lighting modules for U0484 and related rear-lamp or communication codes, and save freeze-frame data before clearing anything.
- With a helper or safe reflection, check the tail, brake, turn, and reverse lamps and compare their operation with scan-tool commands and module A's reported feedback.
- Inspect module A's connectors, rear lamp connectors, grounds, and harness for corrosion, water intrusion, impact damage, or loose connections.
- Check module A's power, ground, and network circuits against the wiring diagram and manufacturer's specification.
- If the rear lighting module or lamps were recently replaced, check manufacturer service information for required configuration or software compatibility.
- If feedback remains inconsistent with commanded lamp operation, follow the manufacturer's procedure to isolate the lamp circuit, module A, or a network fault.
Common fixes
- Repair a loose, corroded, or water-damaged rear lamp connector or harness.
- Restore a faulty ground, power, or network connection to rear lighting module A.
- Replace a confirmed faulty rear lamp or repair its circuit.
- Perform the specified module configuration after replacement.
- Replace rear lighting module A if its feedback remains implausible after circuit checks.
Can I keep driving?
A failed rear brake, turn, or tail lamp can make the vehicle harder to see and can remove an important signal to following drivers. Check all rear lights before driving and avoid driving until failed brake or turn lights are repaired.
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.