What it means
A control module received invalid data from switch input module B. The code identifies a data validity fault; the specific affected function depends on the vehicle.
How it works
Switch input module B collects switch signals and reports their status to other vehicle modules. U04BB is set when a receiving module judges module B's data invalid, distinguishing this code from faults involving switch input module A or C; the affected controls vary by 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 record related communication codes to find which functions are associated with switch input module B.
- Watch module B's live switch-status data while operating the relevant controls and look for missing or implausible changes.
- Inspect module B's connector and harness for loose pins, corrosion, water intrusion, or physical damage.
- Check module B's power and ground against the manufacturer's specification.
- Test the network wiring and connector terminals serving module B for opens, shorts, or poor connections using the wiring information.
- If the wiring and supplies pass, check for a software or configuration mismatch before considering module replacement.
Common fixes
- Reconnect or repair a loose or corroded module B connector.
- Repair damaged wiring or network connector terminals serving switch input module B.
- Restore a faulty power or ground connection at module B.
- Correct an applicable software or configuration issue.
- Replace switch input module B or the receiving module only after tests confirm the source of invalid data.
Can I keep driving?
If the affected controls are nonessential and there are no safety warnings, a short drive may be possible while you arrange diagnosis. Do not drive if module B affects a safety-related control, lighting, visibility, or vehicle operation.
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.