What this code means
U0038 may indicate a PT-CAN bus-off communication problem where the PCM can have trouble sending information to another control unit over the PT-CAN C network.
What the vehicle may do
- The vehicle may show warning lights or network-related messages.
- Some control modules may have limited or abnormal communication.
- Driveability or system behavior may feel unusual depending on which communication messages are affected.
Possible fault areas
- Possible PT-CAN communication path issue.
- Possible network connection or gateway-related issue.
- Possible PCM-side communication concern.
Diagnostic path
Code overview
For this Honda Civic with the 1.5 turbo, U0038 points to a PT-CAN bus-off problem at the PCM. In plain language, the PCM may not be able to send a signal to another control unit over the PT-CAN C network, so it sets the code. The vehicle may show network-related symptoms, warning lights, limited module communication, or other control-system behavior that does not feel normal. Keep the fault areas broad at this stage: a possible communication path problem, a possible network connection issue, or a possible PCM-side communication concern.
Start the diagnostic path
Before getting into the code-specific path, start with the basic system checks and follow a structured diagnostic approach. Do not jump straight to a component call. Make sure the scan, code status, and general network condition are understood first, because this code is about communication, not a single sensor signal.
Use the bus-off communication path
Once the basics are handled, move into the bus-off diagnostic path for a CAN bus that is not connected to the CAN gateway. That is the shared communication fault path that applies here. Treat U0038 as a PT-CAN communication failure from the PCM side, and work the network logic in order instead of guessing at a module or harness fault.
Confirm the code behavior
Keep verification separate from the network testing. For the confirmation procedure, turn the vehicle to the ON mode, and wait 6 seconds. After that, check whether the code behavior matches the fault you are chasing.
Takeaway
The key point with U0038 is to diagnose it as a PT-CAN bus-off communication problem, not as an isolated part failure. Start with the basic checks, follow the correct bus-off path, then verify the code with the ON-mode confirmation step. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0038 is best approached as a communication-network diagnosis: confirm the basic conditions, follow the bus-off path, and verify the code behavior separately.
For more guided automotive diagnostics, visit STEP Diagnostics.
