What this code means
U0104 can indicate a possible communication problem where the VSA control unit may not be receiving expected F-CAN communication from the module associated with this code.
What the vehicle may do
- The vehicle may show stability or brake-related warning indicators.
- Some stability-related functions may be limited while the fault is active.
- The concern may be intermittent, and the vehicle can sometimes appear to operate normally.
Possible fault areas
- Possible voltage supply or ground issue at the transmitting control unit.
- Possible loose terminal or poor connector contact at the transmitting control unit or VSA modulator-control unit.
- Possible open in the F-CAN_H or F-CAN_L communication wiring.
- Possible transmitting control unit fault after the required circuit checks pass.
Diagnostic path
Open on U0104
On this 2010 to 2017 Honda Accord with the 2.4 gas engine, U0104 is a communication code on the VSA control unit side of the F-CAN network. In plain terms, the VSA unit may not be hearing properly from the module tied to this code. The vehicle may set warning lights, may disable some stability-related functions, or may act normal while the fault is only intermittent. Broadly, this can come from a possible power or ground issue at the transmitting module, a connection problem, or an open on the F-CAN_H or F-CAN_L lines. Start with the basic system checks, and if other codes are present, check what they mean first without getting pulled away from the U0104 path.
Pre-check before chasing the network
Before going after the CAN wiring, make sure the multipurpose camera unit has its voltage supply and ground. A loss of voltage supply or ground at the transmitting control unit can store this kind of communication code, so do not skip that basic check and jump straight into wiring.
Confirm the problem first
Turn the vehicle to ON mode. Clear the DTC with the HDS. Then turn the vehicle to OFF, LOCK mode, start the engine, and check for DTCs again with the HDS. If U0104 comes back, continue into the circuit check. If it does not come back, treat it as an intermittent fault for now. At that point, the system is OK at this time, so inspect for poor connections or loose terminals at the multipurpose camera unit and at the VSA modulator-control unit. If captured data is available for the code, try to reproduce the same conditions instead of guessing.
Set up the open-wire check
With the vehicle in OFF, LOCK mode, disconnect the VSA modulator-control unit 38P connector. Then disconnect the transmitting control unit connector for the code you are working on. For U0104, that path is the multipurpose camera unit. During connector setup, jump the SCS line with the HDS, and wait more than 1 minute before continuing. The goal here is to isolate the F-CAN_H and F-CAN_L circuits between the VSA unit and that transmitting unit.
Check both CAN circuits for continuity
Still in vehicle OFF, LOCK mode, check continuity between the receiving control unit and the transmitting control unit on both the F-CAN_H circuit and the F-CAN_L circuit. If both circuits have continuity, the F-CAN_H and F-CAN_L wires are OK at this time, and the U0104 path points to replacing the multipurpose camera unit. If continuity is not present, repair the open in the F-CAN_H and/or F-CAN_L wiring between the VSA modulator-control unit and the multipurpose camera unit.
Verify after the repair
Keep verification separate from the circuit test. After the repair, run the same code check again: clear the DTC with the HDS, turn the vehicle to OFF, LOCK mode, start the engine, and check for DTCs. The takeaway is simple: for U0104, confirm the code first, verify power and ground at the multipurpose camera unit, then prove the F-CAN_H and F-CAN_L paths before condemning the module. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0104 is best approached as a communication-path diagnosis: confirm the code, check basic power and ground, test the CAN circuits, and verify the repair.
For more guided automotive diagnostics, visit STEP Diagnostics.
