What this code means
U0104 may mean the PCM is not receiving normal communication from the multipurpose camera unit.
What the vehicle may do
- The vehicle may display warning messages.
- Camera-based driver assistance functions may be limited or unavailable.
- The vehicle may still drive normally depending on the fault and system state.
Possible fault areas
- Possible multipurpose camera unit start-up issue.
- Possible power or ground circuit issue at the multipurpose camera unit.
- Possible PF-CAN communication path issue.
- Possible gateway-related communication path issue.
Diagnostic path
Opening context
On this Civic, U0104 is a communication code. In plain terms, the PCM may not be getting a usable message from the multipurpose camera unit over the PF-CAN line. The vehicle may show warning messages or lose some camera-based functions, and the broad fault areas can include the camera unit not starting up normally, its power or ground feed, or the network communication path. The key is not to jump straight to a module. Start with the basic troubleshooting approach and prove the camera can power up before chasing the CAN side.
How the code sets
The code sets when the PCM cannot receive the signal from the multipurpose camera unit through the PF-CAN line, or when the information coming from that camera unit is abnormal continuously for the specified cycle. So the diagnostic direction is simple: first make sure the camera unit is actually alive, then move into the communication path if it is.
First check the camera unit power and ground
Before getting deep into network diagnosis, check the power and ground circuit for the multipurpose camera unit. This matters because this code may store if that camera unit does not start normally, and a power or ground circuit fault can create the same lost-communication symptom. If the camera is not waking up, the network fault may only be a result, not the root problem.
Then follow the F-CAN communication path
Once the camera unit power and ground side has been checked, continue the lost-communication diagnosis on the F-CAN path with the bus connection to the gateway in mind. Stay structured here: do not assume the PCM, camera unit, or gateway is bad just because the code names communication. Prove where communication is being lost.
Reproduce the operating condition
For confirmation, turn the vehicle to ON mode and wait 6 seconds. That is the monitor gate for this check. After that, see whether U0104 resets under the same condition, and keep verification separate from the circuit and network testing.
Wrap-up
The takeaway: with U0104, treat the multipurpose camera unit power-up check as the first priority, then work the communication path in order and verify the code stays gone under the ON-mode check. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0104 is often approached as a communication problem, but the camera unit power and ground check comes first.
For more guided automotive diagnostics, visit STEP Diagnostics.
