What it means
A control module received invalid data from switch input module C. The code identifies a data validity fault; the specific affected function depends on the vehicle.
How it works
Switch input module C gathers switch signals and sends their status to other modules. U04BC is set when a receiving module considers module C's data invalid, specifically identifying module C's reported information; which switch-operated functions are affected depends on the vehicle.
Common causes
Most likely first.
- Fault in the transmitting module
- Network wiring or connector fault
- Module power or ground fault
- Software or configuration mismatch
Symptoms
- One or more switch-operated functions may not work correctly
- Related communication codes may appear
How to diagnose it
- Scan all modules and note related communication codes to determine which vehicle functions use switch input module C.
- Monitor module C's live switch-status data while operating the associated controls and check for missing or implausible changes.
- Inspect module C's connector and harness for loose pins, corrosion, moisture, or damaged wiring.
- Check module C's power and ground against the manufacturer's specification.
- Test the network wiring and connector terminals serving module C for opens, shorts, or poor connections using the vehicle wiring information.
- If wiring and supplies are sound, check software and configuration compatibility before replacing a module.
Common fixes
- Reconnect or repair a loose or corroded module C connector.
- Repair damaged network wiring or connector terminals serving switch input module C.
- Restore a faulty power or ground connection at module C.
- Correct an applicable software or configuration issue.
- Replace switch input module C or the receiving module only after testing confirms the fault source.
Can I keep driving?
If only nonessential switch functions are affected and no safety warning is present, the vehicle may be usable for a short time while diagnosis is arranged. Avoid driving if the affected controls are needed for safe braking, steering, lighting, or visibility.
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.