What it means
A control module has stopped receiving expected messages from rear lighting control module B. The code identifies the communication loss; lamps controlled by the module may be affected.
How it works
Rear lighting control module B manages the rear lighting functions assigned to it and communicates status over the vehicle network. U0252 sets when another module stops receiving the expected messages from this rear lighting module; it does not specify which lamp or function is affected.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- One or more rear lighting functions may be unavailable or limited
- A lighting warning may appear depending on the vehicle
How to diagnose it
- Scan all modules and save freeze-frame and communication data, noting any other lighting or network codes.
- With the vehicle safely parked, check the rear lamps and warnings to identify any lighting functions that are inoperative or limited.
- Inspect module B's connector and nearby rear harness for water intrusion, corrosion, loose terminals, or physical damage.
- Check the module's power and ground using the manufacturer's specified method.
- Test the network wiring to rear lighting module B for opens or shorts using vehicle-specific wiring information.
- If power, ground, and bus wiring are sound, follow the manufacturer's communication checks before replacing the module.
Common fixes
- Reconnect and secure a loose module connector.
- Repair damaged, corroded, or water-affected wiring and connector terminals.
- Restore a failed power feed or ground to rear lighting module B.
- Replace module B only after its supplies and communication circuit pass testing.
Can I keep driving?
Check all rear lamps before driving, since functions controlled by module B may not work and can reduce visibility or make the vehicle harder to signal to others. Avoid driving in poor visibility or traffic until required lighting is confirmed operational.
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.