What this code means
U128D may indicate that the BSI radar unit is not receiving an expected gauge control module signal over B-CAN.
What the vehicle may do
- The vehicle may show a BSI-related warning or network communication warning.
- The concern may sometimes appear mainly as a stored diagnostic code.
Possible fault areas
- Gauge control module startup may be involved.
- Gauge control module power or ground circuits can be possible fault areas.
- The B-CAN communication path may be involved.
Diagnostic path
Opening context
On this Accord Hybrid, U128D is a network communication code tied to the BSI radar unit. In plain language, the radar unit may not be receiving the gauge control module message it expects over B-CAN. The vehicle may show a BSI-related warning, a network communication warning, or sometimes the symptom may be limited to the stored code. The broad areas to keep in mind are gauge control module startup, gauge control module power and ground, and the B-CAN communication path.
Start with the right checks
Before going straight after the radar unit, start with the basic system checks and follow a structured diagnostic approach. This code can store if the gauge control module does not start normally. It can also store from a power or ground circuit failure at the gauge control module, so check that power and ground side first before treating this as a deeper network fault.
Confirm the monitor condition
To bring the fault condition back up, turn the vehicle to the ON mode, then wait for at least 5 seconds. That is the confirmation condition for this code, so keep that timing clean before judging whether the fault is present.
Follow the communication path
If U128D is still the code you are working, the diagnostic direction is B-CAN lost communication. The logic is simple: the BSI radar unit is looking for gauge control module communication on B-CAN, and if that message is missing, the radar unit sets the code. So the next testing should stay focused on why that gauge control module signal is not being received, with the power and ground check handled first.
Verification and close
After the issue in that power, ground, startup, or B-CAN communication path has been addressed, keep verification separate from testing. Put the vehicle back in ON mode, wait for at least 5 seconds, and confirm U128D does not reset under that same condition. The takeaway: do not condemn the BSI radar unit just because it reported the code; prove the gauge control module can wake up, is powered and grounded correctly, and can communicate on B-CAN. For more diagnostic training, visit stepdiagnostics.com.
Final check
For U128D, prove gauge control module startup, power, ground, and B-CAN communication before focusing on the BSI radar unit itself.
For more guided automotive diagnostics, visit STEP Diagnostics.
