What this code means
U128F may indicate that the right side blind spot information radar unit is not receiving expected B-CAN communication from the left side blind spot information radar unit.
What the vehicle may do
- The vehicle may show blind spot information warnings.
- Driver support features can be limited while the fault is active.
- The fault may be intermittent if the communication or module startup concern is intermittent.
Possible fault areas
- Possible B-CAN communication concern between the BSI radar units.
- Possible left side BSI radar unit startup concern.
- Possible power or ground concern affecting the left side BSI radar unit.
Diagnostic path
Opening context
On this Accord Hybrid, U128F is a blind spot information communication fault. In plain language, the right side BSI radar unit may not be receiving the expected B-CAN signal from the left side BSI radar unit. The vehicle may show blind spot information warnings, and driver support functions can be limited while the fault is active. The broad fault areas are possible B-CAN communication trouble, a left side radar unit that may not be starting up normally, or a possible power and ground issue feeding that left side unit.
Start the troubleshooting path
Before you get deep into the code, start with the basic troubleshooting approach for the system. Make sure you are not skipping the usual checks that can change the direction of the diagnosis, then keep this fault centered on the BSI communication path.
Diagnostic direction
The logic for this code is straightforward: if the right side BSI radar unit cannot receive the left side BSI radar unit signal over B-CAN, it calls that abnormal and stores U128F. Before chasing the network side too deeply, check the left side BSI radar unit’s power and ground circuit first, because a power or ground failure there can cause this code. Also keep in mind that the code may set if the left side BSI radar unit does not start normally.
Network troubleshooting path
Once the left side unit power and ground check is not pointing you somewhere obvious, continue with the B-CAN lost communication troubleshooting path for this fault. This is a network communication diagnosis, so avoid jumping straight to a radar unit conclusion just because the code names the BSI system. Use the BSI data list in the scan tool to help watch what the system is reporting while you work the communication fault.
Confirmation procedure
For the confirmation step, turn the vehicle to the ON mode, then wait for at least 5 seconds. That gives the system the opportunity to run the check for this communication fault.
Takeaway and close
The takeaway for U128F is to treat it as a B-CAN communication problem between the two BSI radar units, with the left side unit’s startup, power, and ground checked early in the process. For more diagnostic training, visit stepdiagnostics.com.
Final check
U128F is often approached as a communication-path diagnosis, with left side radar unit startup, power, and ground considered early.
For more guided automotive diagnostics, visit STEP Diagnostics.
