What this code means
U0029 may indicate that the PCM is having a communication problem sending a message across the PF-CAN A network.
What the vehicle may do
- The vehicle may show warning lights.
- A scan tool may have communication trouble with one or more modules.
- Symptoms can sometimes appear to involve more than one control unit.
Possible fault areas
- Possible network communication path concern between the PCM and other control units.
- Possible CAN gateway or PF-CAN A communication-related issue.
Diagnostic path
Opening context
On this 2016 to 2024 Honda Civic with the 2.0 liter gas engine, U0029 is a communication-related fault in the PGM-FI side of the system. In plain language, the PCM may be having trouble sending a message across the PF-CAN A network. The vehicle may show warning lights, communication-related scan tool problems, or symptoms that seem to involve more than one module. Broadly, the possible fault area is the network communication path between the PCM and other control units, so approach this as a network diagnosis, not as a single sensor code.
First priority check
Before going after U0029 directly, start with the basic system checks and follow a structured diagnostic approach. If a CAN gateway network communication fault is stored at the same time, diagnose that first. That matters because the gateway side can affect how the rest of the network communicates, and chasing the PCM-side fault before clearing up that higher-priority network issue can send you in the wrong direction.
How the code sets
For U0029, the setting logic is straightforward: if the PCM cannot send a signal to another unit through PF-CAN A, the PCM sees that as an abnormal communication condition and stores the code. So the diagnostic direction is to confirm whether the problem is truly in that communication path, instead of assuming the PCM or another module is bad.
Diagnostic approach
After the priority network fault check is handled, keep the diagnosis focused on communication. Reproduce the operating conditions as needed, look at what the scan tool can and cannot communicate with, and use the structured network path for the CAN gateway or PF-CAN A side before making any repair decision. This information supports a network communication diagnosis; it does not support jumping straight to a part replacement.
Verification
Once the communication issue has been addressed through the proper network diagnostic path, verify the repair separately. Clear the fault, operate the vehicle under the conditions needed to run the monitor, and confirm U0029 does not reset. The takeaway is simple: with U0029, prioritize any gateway communication fault first, then prove out the PF-CAN A communication path before condemning parts. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0029 is best approached as a network communication diagnosis, with any higher-priority gateway communication fault handled first.
For more guided automotive diagnostics, visit STEP Diagnostics.
