What this code means
U129E is an F-CAN malfunction. It may mean the PCM is seeing a communication problem on the network path involving the keyless access control unit.
What the vehicle may do
- The vehicle may show keyless access warning behavior.
- The code may be found during a scan even when obvious drivability symptoms are limited.
- Communication with the keyless access system may be affected.
Possible fault areas
- Possible F-CAN network communication issue.
- Possible poor connector contact or loose terminals at the keyless access control unit or PCM.
- Possible open in the F-CAN_H or F-CAN_L wiring.
- Possible keyless access control unit fault.
Diagnostic path
Open
U129E is an F-CAN malfunction. In plain language, the PCM may not be seeing the expected communication on the network path that involves the keyless access control unit. Depending on the vehicle, the driver may notice keyless access warning behavior, or the code may show up during a scan with few obvious symptoms. The broad fault areas can include a network communication issue, poor connector or terminal contact at the keyless access control unit or PCM, an open in either F-CAN wire, or possibly the keyless access control unit itself. Before you troubleshoot, start with the basic system checks, then work this code in order instead of jumping straight to parts.
Initial code check
First, turn the ignition switch to ON (II), or press the engine start/stop button to select ON mode. Use the HDS and check for Pending or Confirmed DTCs. If U129E is present at the same time as the related F-CAN code, handle that related code path first. If U129E is not paired with that related code, continue with the U129E checks.
Clear and see if U129E returns
Next, clear the DTC with the HDS, then check again for Pending or Confirmed DTCs. If U129E comes right back, keep going. If U129E does not come back, treat it as an intermittent failure and consider the system OK at that moment. In that case, inspect for poor connections or loose terminals at the keyless access control unit and the PCM. If captured failure information is available, try to reproduce the same conditions that were present when the code recorded.
Check keyless access communication
Now use the HDS to check communication with the keyless access system. If the HDS communicates with the keyless access control unit, move on to the F-CAN wire checks. If it does not communicate, do not guess at the network wiring yet. Move into the keyless access system symptom diagnosis first, because that communication failure changes the path.
Check the F-CAN_H wire for an open
For the high-side F-CAN wire check, turn the ignition switch to LOCK (0), or press the engine start/stop button to select OFF mode. Jump the SCS line with the HDS. Then disconnect PCM connector A (51P) and keyless access control unit connector C (24P). Check continuity between keyless access control unit connector C (24P) No. 4 (WHT) and PCM connector A (51P) No. 2 (WHT). If there is continuity, continue to the low-side wire. If there is no continuity, repair the open in the F-CAN_H wire between the PCM (A2) and the keyless access control unit.
Check the F-CAN_L wire and finish the path
Next, check continuity on the low-side F-CAN wire between keyless access control unit connector C (24P) No. 5 (RED) and PCM connector A (51P) No. 1 (RED). If there is no continuity, repair the open in the F-CAN_L wire between the PCM (A1) and the keyless access control unit. If there is continuity on this wire as well, the path ends with replacement of the keyless access control unit.
Verification and takeaway
Once the repair path is complete, use the same clear-and-recheck logic to confirm U129E does not return as a Pending or Confirmed DTC. The key to this diagnosis is staying in sequence: check whether another network code should be handled first, confirm U129E is repeatable, verify communication with the keyless access control unit, then prove both F-CAN wires before condemning the module. For more diagnostic training, visit stepdiagnostics.com.
Final check
Work the code in order: confirm whether it is paired with the related network code, see if U129E returns after clearing, check keyless access communication, then test both F-CAN wires before reaching
For more guided automotive diagnostics, visit STEP Diagnostics.
