What this code means
U0100 may mean the real time AWD control unit has lost communication with the PCM on the F-CAN network.
What the vehicle may do
- The vehicle may show AWD or other warning lights.
- AWD operation may be affected.
- The driver may notice no obvious symptom other than a stored code.
Possible fault areas
- Possible open or poor connection in the F-CAN wiring between the real time AWD control unit and PCM.
- Possible connector or terminal condition affecting network communication.
- Possible PCM software or PCM communication concern.
- Other PGM-FI faults may need to be addressed first.
Diagnostic path
Opening context
On this 2010 to 2016 Honda CR-V with the 2.4 gas engine, U0100 is a communication fault. In plain terms, the real time AWD control unit may not be hearing the PCM correctly on the F-CAN network. The vehicle may show AWD or other warning lights, AWD operation may be affected, or the driver may not notice much beyond the stored code. Broadly, think possible network wiring trouble, connector issues, PCM software or module communication issues, and any engine-control codes that may need attention first. Before diving in, start with the basic system checks and handle any PGM-FI codes first.
Confirm the fault
First, verify that the fault is actually present. Turn the vehicle to the ON mode, clear the code with the HDS, then turn the vehicle to OFF, or LOCK. Start the engine and check codes again with the HDS. If U0100 comes right back, the failure is duplicated and you move into the F-CAN wiring check between the real time AWD control unit and the PCM. If the code does not return, treat it as intermittent. The system is OK at that moment, and if captured data or an onboard snapshot was recorded, try to reproduce the captured conditions instead of guessing. If a different companion communication fault returns, use that result to choose the matching network branch, but keep this diagnosis centered on the fault that actually duplicated.
Check the F-CAN lines to the PCM
For the U0100 path, turn the vehicle back to OFF, or LOCK, and wait 2 minutes. Then jump the SCS line with the HDS and wait more than 1 minute. Disconnect the real time AWD control unit 24P connector and PCM connector A, the 51P connector. Now check continuity on the two F-CAN circuits: real time AWD control unit 24P connector No. 14 to PCM connector A 51P No. 2, and real time AWD control unit 24P connector No. 24 to PCM connector A 51P No. 1.
Use the PCM-path continuity result
If there is continuity, the wiring path is not the failed part of this check. At that point, update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom or indication goes away after the PCM update, that completes the troubleshooting. If it goes away with the known-good PCM, replace the original PCM. If there is no continuity, repair the open in the F-CAN_H and/or F-CAN_L wiring between the real time AWD control unit and the PCM.
If the VSA communication path is the one that duplicated
If the first check points to the VSA communication path instead of the PCM path, turn the vehicle to OFF, or LOCK. Disconnect the real time AWD control unit 24P connector and the VSA modulator-control unit 38P connector. Check continuity on each F-CAN line individually: real time AWD control unit 24P connector No. 14 to VSA modulator-control unit 38P connector No. 38, and real time AWD control unit 24P connector No. 24 to VSA modulator-control unit 38P connector No. 26. If there is continuity, update the VSA modulator-control unit if it does not have the latest software, then recheck. If the symptom or indication goes away with the update, troubleshooting is complete. If it does not go away with the updated VSA modulator-control unit, replace the VSA modulator-control unit. If there is no continuity, repair the open in the F-CAN_H and/or F-CAN_L wiring between the real time AWD control unit and the VSA modulator-control unit.
If the steering angle communication path is the one that duplicated
If the first check points to the steering angle sensor communication path, turn the vehicle to OFF, or LOCK. Disconnect the real time AWD control unit 24P connector and the steering angle sensor 4P connector. Check continuity from real time AWD control unit 24P connector No. 14 to steering angle sensor 4P connector No. 2, and from real time AWD control unit 24P connector No. 24 to steering angle sensor 4P connector No. 3. If there is continuity, replace the steering angle sensor. If there is no continuity, repair the open in the F-CAN_H and/or F-CAN_L wiring between the real time AWD control unit and the steering angle sensor.
Verification and takeaway
Keep verification separate from the wiring test. After the directed action, use the HDS recheck called for in the diagnostic path to confirm the symptom or indication is gone. For U0100, the takeaway is simple: confirm the code first, prove the F-CAN path between the AWD control unit and PCM, then only move toward PCM software or PCM substitution when the wiring checks good. For more diagnostic training, visit stepdiagnostics.com.
Final check
Confirm the fault, check the F-CAN continuity to the PCM, and only move to PCM software or PCM comparison after the wiring path checks good.
For more guided automotive diagnostics, visit STEP Diagnostics.
