What it means
The vehicle bus reports loss of communication with the trailer backup assist module. Steer-by-knob trailer reverse guidance, hitch angle sensing and trajectory planning are unavailable.
How it works
The trailer backup assist control module uses hitch-angle and vehicle information to guide a trailer's path during reversing. The network monitors messages from this module and sets this code when communication is lost. Steer-by-knob guidance, hitch-angle sensing and trajectory planning may then be unavailable.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
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 all modules and save event data to see when the trailer backup assist module stopped responding and whether trailer or network faults were also recorded.
- Check live data and the display for module status, hitch-angle availability and any indication that the system cannot identify the trailer.
- Inspect the module connector, trailer-related connectors and nearby bus wiring for corrosion, looseness, water entry or damage.
- Check the module's specified power and ground according to the manufacturer's service information.
- Test the communication circuit to the trailer backup assist module for opens, shorts or poor connections using the manufacturer's network procedure.
- If wiring and supply checks pass, follow the manufacturer's procedure to test the module and verify guidance operation with a correctly connected trailer.
Common fixes
- Clean and reconnect a loose or corroded module or trailer-related connector.
- Repair damaged bus wiring or restore the module's specified power or ground.
- Correct a disconnected or damaged hitch-angle sensor connection if the inspection identifies it.
- Replace or reprogram the trailer backup assist module only if diagnostic checks confirm it is faulty.
Can I keep driving?
You can drive without the assist system, but do not use its steer-by-knob guidance or assume it is tracking the trailer's path. Reverse slowly using direct observation and a spotter where visibility is limited.
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.