What this code means
U129E may indicate an F-CAN communication problem involving the PCM communication path through the keyless access control unit.
What the vehicle may do
- The vehicle may show keyless access indicator behavior.
- The code may be intermittent and only return under certain conditions.
- A scan tool may have communication trouble with the keyless access system.
Possible fault areas
- Possible poor connections or loose terminals.
- Possible open circuit in the F-CAN_H or F-CAN_L wiring.
- Possible keyless access control unit concern after the wiring checks pass.
Diagnostic path
What U129E means on this CR-V
On a 2010 to 2016 Honda CR-V with the 2.4 gas engine, U129E is a communication fault in the PGM-FI side of the system. In plain terms, the PCM may not be seeing the expected F-CAN communication through the keyless access control unit path. The vehicle may show keyless access indicator behavior, scan tool communication trouble with the keyless access system, or an intermittent code that only shows up under certain conditions. The broad fault areas can include poor terminal contact, an open in one side of the F-CAN circuit, or a possible keyless access control unit issue. Start with the basic system checks, then work the code in order so you do not turn a communication problem into a parts guess.
First, prove whether the fault is present
Begin by turning the vehicle to the ON mode. Use the HDS to clear the code, then check pending and confirmed codes with the HDS. If U129E comes right back, the failure is duplicated and you move forward with the communication checks. If U129E does not come back, treat it as an intermittent failure. The system is OK at that moment, so look for poor connections or loose terminals around the keyless access control unit and the affected communication path. If captured failure data is available, try to reproduce the same operating conditions instead of guessing.
Check whether the scan tool can talk to keyless access
Next, check communication to the keyless access system with the HDS. If the HDS communicates with the keyless access system, continue into the F-CAN circuit checks. If it does not communicate, stop this U129E path and move into the keyless access symptom diagnosis for an indicator that does not go off or does not come on. That result changes the direction of the diagnosis.
Check the F-CAN_H circuit for an open
For the F-CAN_H open check, turn the vehicle to the OFF, LOCK mode. Jump the SCS line with the HDS and wait more than 1 minute. Then disconnect PCM connector A, which is the 51P connector, and keyless access control unit connector C, which is the 24P connector. With those connectors disconnected, check continuity from keyless access control unit connector C, terminal No. 4, to PCM connector A, terminal No. 2. If there is continuity, the F-CAN_H wire is OK and you continue to the low side check. If there is no continuity, repair the open in the F-CAN_H wire between PCM A2 and the keyless access control unit.
Check the F-CAN_L circuit and finish the branch
Now check the F-CAN_L side under the same test condition: vehicle OFF, LOCK mode, PCM connector A 51P disconnected, and keyless access control unit connector C 24P disconnected. Check continuity from keyless access control unit connector C, terminal No. 5, to PCM connector A, terminal No. 1. If there is no continuity, repair the open in the F-CAN_L wire between PCM A1 and the keyless access control unit. If continuity is present, the F-CAN_L wire is OK. At that point, substitute a known-good keyless access control unit and recheck. If U129E is not indicated after the known-good unit is installed, replace the original keyless access control unit.
Takeaway
The clean way through U129E is to verify the code first, confirm keyless access communication, then prove both F-CAN legs before calling the control unit. Keep verification separate from the circuit testing, and let the branch result tell you where to go next. For more diagnostic training, visit stepdiagnostics.com.
Final check
Verify the code, confirm keyless access communication, and prove both F-CAN circuits before drawing a module conclusion.
For more guided automotive diagnostics, visit STEP Diagnostics.
