What it means
A control module has stopped receiving expected network messages from the trailer brake control switch. The effect on trailer brake control depends on the vehicle's system design.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
The trailer brake control switch sends network messages that let the vehicle recognize driver commands for trailer braking. This code sets when a receiving module no longer gets the expected messages from that switch; trailer brake availability then depends on the vehicle's design.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Warning light or message related to the affected system
- Trailer brake control input may be unavailable
How to diagnose it
- Record freeze-frame data and scan all modules for related communication or trailer-brake codes to identify when the messages stopped and which modules are affected.
- Check whether the trailer-brake warning is present and whether the switch inputs appear in live data while operating the controls.
- Inspect the trailer brake control switch connector and nearby network wiring for loose connections, corrosion, damage, or chafing.
- Check the switch module's power and ground under the conditions specified by the manufacturer.
- Test the network wiring to the switch module for opens or shorts using the manufacturer's procedure, then assess the module only after wiring and power checks pass.
Common fixes
- Reconnect or clean a loose or corroded trailer brake control switch connector.
- Repair damaged network wiring or its connections.
- Restore the switch module's power or ground connection.
- Replace the trailer brake control switch module if its power, ground, and network circuits test correctly but communication remains absent.
Can I keep driving?
Trailer brake commands may be unavailable, so avoid towing until you confirm the trailer brakes work and the warning is resolved. If braking response is uncertain, do not drive with a trailer.
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.