What this code means
U0104 may indicate that the PCM is not receiving normal communication from the multipurpose camera unit over the vehicle network.
What the vehicle may do
- The vehicle may display driving-support or network-related warnings.
- Some driver-assistance functions may be limited or unavailable while the communication fault is present.
Possible fault areas
- Possible multipurpose camera unit startup issue.
- Possible multipurpose camera unit power or ground circuit issue.
- Possible PF-CAN communication path issue between the camera unit, gateway side of the network, and PCM.
Diagnostic path
Opening context
On this 2016 to 2024 Honda Civic with the 2.0L engine, U0104 is a network communication code. In plain terms, the PCM may not be getting a normal message from the multipurpose camera unit over the PF-CAN line. The vehicle may show driving-support related warnings, and the fault area can involve the camera unit starting up, its power and ground supply, or the communication path between the camera unit, the gateway side of the network, and the PCM.
What makes the code set
The diagnostic logic is straightforward: if the PCM cannot receive the signal from the multipurpose camera unit over the PF-CAN line, or if the information coming from that unit is abnormal continuously for the specified cycle, the PCM sets U0104. Also keep in mind, this code may store if the multipurpose camera unit does not start normally.
Start the diagnostic path
Before getting deep into network testing, start with the basic system checks and follow a structured diagnostic approach. Then check the power and ground circuit for the multipurpose camera unit first. That is called out before the rest of the U0104 path because a camera unit that is not powered up correctly can look like a communication failure from the PCM’s point of view.
Network path caution
After the camera unit power and ground checks, the diagnostic path moves into the F-CAN lost-communication checks for the CAN bus connection through the gateway. The detailed test steps for that network path are not available here, so do not guess at wire checks or module conclusions. Pause, recheck the earlier diagnostic path, and use the correct network test information before making a call.
Confirmation and verification
To reproduce the operating conditions for this code, turn the vehicle to the ON mode and wait 6 seconds. Keep verification separate from the testing work: after the fault path is addressed, verify the repair and confirm U0104 stays gone under that same ON-mode confirmation condition.
Takeaway and CTA
The key takeaway is to treat U0104 as a communication complaint, but do not skip the camera unit power and ground check before moving into CAN network diagnostics. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0104 is often approached by confirming the camera unit can power up normally before moving deeper into network communication testing.
For more guided automotive diagnostics, visit STEP Diagnostics.
