What does it mean?
B1671 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Right Trailer Tow Lamp Control Circuit Open .
Symptoms
- No output at all to the right trailer lamps when a trailer is connected
- Trailer lighting fault message shown as soon as a trailer is detected
- Trailer detection may not work at all, so trailer stability assistance stays off
- Right side trailer indicator and tail lamp both dead, while the left side works
- The code appeared immediately after a towbar or wiring kit was installed
Likely causes
- Trailer harness connector unplugged or never connected after a towbar was fitted
- Broken wire in the trailer harness, often at the point where it is clipped under the rear bumper
- Trailer socket internally damaged, with a terminal pushed out or burnt away
- Both right side trailer lamps burned out or the trailer harness left open
- Module configured for a towing package that is not actually fitted, or a replaced module not coded to the vehicle
- Water inside the socket that has corroded a pin until the connection is lost
- Open output driver in the towing or body control module
How to fix it
- Connect a trailer test box and confirm which outputs are missing
- Verify that the trailer harness is plugged into the vehicle and that the socket is securely mounted
- Inspect the socket internally for burnt, corroded or pushed out terminals
- Measure for voltage at the socket pin while the function is commanded, then check continuity of that wire back to the module
- Follow the harness under the rear of the vehicle and check the clipped and taped sections for breaks
- Confirm that the vehicle configuration matches the fitted towing equipment, especially after a module replacement or a retrofit installation
- Repair the open circuit or renew the socket, then retest every trailer lamp function