What this code means
U0029 may indicate a PF-CAN A bus-off communication problem involving the PCM, where the PCM may not be able to send messages normally to other units on that network.
What the vehicle may do
- The vehicle may show network-related warning behavior.
- Scan tool communication may be limited or inconsistent.
- Other module communication symptoms can be possible, depending on the network condition.
Possible fault areas
- Possible network communication fault
- Possible gateway-side communication issue
- Possible PCM communication path concern
Diagnostic path
Opening context
On this 2016 to 2024 Honda Civic with the 1.5L engine, U0029 points to a PF-CAN A bus-off type communication problem at the PCM. In plain terms, the PCM may not be able to send its message out to the other modules on that network. The vehicle may show network-related warning behavior, limited communication, or scan tool communication issues, depending on what else is happening. Broadly, think in terms of a possible network communication fault, a possible gateway-side issue, or a possible PCM communication path problem. We are not jumping to a part here. The diagnostic path starts with the network logic.
Start with the basic checks
Before getting deep into the code chart, start with the basic system checks and follow a structured diagnostic approach. With a communication code like this, that matters. You want to know whether this is an isolated PCM-side network fault, or whether the scan is showing a broader network condition that needs to be handled first.
Check for the gateway-first condition
Next, look at the complete scan results. If a matching gateway-side version of this PF-CAN A bus-off fault is stored at the same time, diagnose that gateway network fault first. That is the key branch in this path. The logic is that the gateway-side fault can affect how this PCM communication fault is being seen, so do not chase the PCM-side code ahead of it.
If the gateway condition is not present
If that gateway-first condition is not present, pause and continue with the earlier structured diagnostic path for this target code. Do not guess at a repair from the code name alone. This code sets when the PCM cannot send a signal to another unit over PF-CAN A, so the diagnosis needs to stay focused on confirming the network communication path rather than assuming a failed module.
Takeaway
The main takeaway for U0029 is simple: treat it as a PF-CAN A communication problem at the PCM, but check the complete network scan first. If the gateway-side companion condition is stored at the same time, handle that first; otherwise, stay with the structured diagnostic path and avoid guessing. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code often needs a network-first diagnostic approach, especially when a related gateway-side condition is present at the same time.
For more guided automotive diagnostics, visit STEP Diagnostics.
