What this code means
U0104 may mean the gauge control module is not receiving expected communication from the driving support system control unit or related radar communication path.
What the vehicle may do
- The vehicle may show warning messages in the gauge display.
- Driving support features may be limited or unavailable.
- The code can appear when the radar side does not wake up or communicate normally.
Possible fault areas
- Possible network communication fault
- Possible millimeter wave radar power or ground issue
- Possible module start-up or wake-up issue
- Possible gateway or CAN communication path issue
Diagnostic path
Opening context
This one is U0104 on a 2018 to 2025 Honda Accord 2.0 Hybrid. In plain terms, the gauge control module may not be receiving the data it expects from the driving support side of the vehicle, specifically through the millimeter wave radar communication path. The driver may see warning messages, driving support features may be limited, and the cluster may report a communication fault. Broadly, think possible network communication trouble, module wake-up trouble, or a power and ground issue affecting the radar before you start chasing the rest of the bus.
Before testing
Start with the basic system checks and follow a structured diagnostic approach. If other codes are present, check what they mean first and handle the network diagnosis in the proper order rather than treating this code by itself too early.
Key setup checks
A couple of points matter before you go deep. This code may set if the millimeter wave radar does not start normally. It may also set from a power or ground circuit failure at the millimeter wave radar, so check that power and ground side first before moving on with this troubleshooting.
Begin the diagnostic path
Turn the vehicle to ON mode. With the vehicle awake, use HDS in Body Electrical, Gauges, Data List to look at the gauge control module side of the information. The diagnostic logic here is simple: the gauge control module is looking for specified data from the millimeter wave radar. If it cannot receive that data, it judges the condition abnormal and stores U0104.
Network fault isolation
From here, the fault isolation follows the F-CAN lost-communication path for the bus connected through the gateway. If that diagnostic path is not available at the vehicle, pause, recheck the earlier checks, and avoid guessing. Do not jump straight to parts. Confirm radar power and ground, confirm the module is waking up normally, then continue with the proper network communication checks.
Verification and takeaway
After any repair or correction, verify the repair and confirm the code stays gone. The takeaway for U0104 is to treat it as a communication complaint: make sure the radar can power up, make sure its power and ground are solid, then follow the F-CAN lost-communication diagnostic path without skipping ahead. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0104 is often approached as a communication fault first, with radar power, ground, module start-up, and the F-CAN communication path kept in view.
For more guided automotive diagnostics, visit STEP Diagnostics.
