What this code means
U0029 may indicate that the PCM has detected a PF-CAN A communication problem where it can’t send a signal to another control unit on that network.
What the vehicle may do
- The vehicle may show communication-related warnings depending on which modules are affected.
- Some systems may behave differently if network messages are missing or interrupted.
- In some cases, the code may be stored with limited obvious symptoms.
Possible fault areas
- PF-CAN A network communication path
- PCM communication
- Possible gateway-side network communication context if a simultaneous fault is present
Diagnostic path
Opening context
On this Honda Civic with the 2.0L engine, U0029 points to a PF-CAN A malfunction, described as a bus-off type communication fault involving the PCM. In plain language, the PCM may not be able to send a message to another control unit on that network. The vehicle may show communication-related warnings, may have module-to-module coordination issues, or may only store the code depending on what else is happening. Think in terms of a possible network communication problem first: the PF-CAN A path, PCM communication, and any gateway-side network context that shows up at the same time.
Start the diagnostic path
Before getting into code-specific checks, make sure the general troubleshooting approach for this system has been reviewed. That keeps the diagnosis structured instead of jumping straight to parts or wiring assumptions.
Handle the priority fault first
If the gateway-side network communication fault for this same condition is stored at the same time, handle that first. That is the priority path before continuing with this PCM-side U0029 diagnosis.
Procedure boundary
The diagnostic path provided for this code stops at the preliminary troubleshooting review and the priority note. It does not give running conditions, setting thresholds, pin checks, branch outcomes, repair steps, or a separate verify-the-repair routine. At that point, pause, recheck the earlier diagnostic path, and avoid guessing beyond the information you actually have.
Takeaway
The takeaway: treat U0029 as a PF-CAN A communication failure from the PCM side, address any simultaneous gateway-side network fault first, and do not invent test steps that are not part of the confirmed path. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code often calls for network-first thinking rather than component-first guessing.
For more guided automotive diagnostics, visit STEP Diagnostics.
