What this code means
U128F generally means the right side blind spot information radar unit may not be receiving expected communication from the left side blind spot information radar unit.
What the vehicle may do
- The blind spot information system may show a warning.
- Blind spot monitoring functions may be limited or unavailable.
- The concern may appear when the system detects missing communication between radar units.
Possible fault areas
- Possible left side BSI radar unit startup issue.
- Possible left side BSI radar unit power or ground issue.
- Possible B-CAN communication issue between the left and right BSI radar units.
Diagnostic path
Open on the code
U128F on this CR-V Hybrid means the right side BSI radar unit is losing communication with the left side BSI radar unit. In plain terms, the right side unit may not be receiving the left side unit’s messages over B-CAN. The vehicle may show a blind spot information warning or the system may not operate normally. The broad fault areas can include the left side radar unit not starting up correctly, a possible power or ground problem at that unit, or a possible B-CAN communication issue between the radar units.
Start with the basics
Before getting deep into the network side, start with the basic system checks. Then go straight to the left side BSI radar unit power and ground circuit. That order matters because this code can set if the left side radar unit does not start normally, and a power or ground failure at that unit can make the right side unit think communication has been lost.
Follow the communication path
Once the left side unit power and ground have been checked, handle the rest of the diagnosis as a B-CAN lost-communication problem. The logic is simple: if the right side BSI radar unit cannot receive the left side BSI radar unit signals through B-CAN, it decides there is an abnormality and stores U128F. Stay on that communication path and avoid guessing at parts.
Confirmation check
Keep verification separate from the testing. For the confirmation check, turn the vehicle to the ON mode, then wait for at least 5 seconds. After that, confirm whether U128F stays gone or comes back under that same basic operating condition.
Takeaway
The main takeaway is to prove the left side radar unit can power up properly first, then treat U128F as a B-CAN communication issue between the two BSI radar units. For more diagnostic training, visit stepdiagnostics.com.
Final check
Check the left side radar unit’s ability to power up first, then continue with the B-CAN communication diagnostic path.
For more guided automotive diagnostics, visit STEP Diagnostics.
