What this code means
U0122 may indicate that the body control module has lost expected communication with the VSA/ABS control side of the vehicle.
What the vehicle may do
- The vehicle may show stability control, traction control, or ABS-related warnings.
- Some brake or stability-assist functions can feel limited or unavailable while communication is missing.
Possible fault areas
- Possible VSA modulator-control unit start-up issue.
- Possible VSA modulator-control unit power or ground circuit issue.
- Possible B-CAN or F-CAN communication path issue.
- Possible gateway or body-control-module-side communication issue.
Diagnostic path
Code overview
On this Civic, U0122 may mean the body control module is not getting the communication it expects from the VSA and ABS side of the vehicle. The driver may see stability, traction, or ABS-related warnings, and those systems can act limited when communication is missing. Broadly, think in terms of VSA modulator-control unit start-up, its power and ground supply, and the network path the body control module uses to receive that data.
Start with the right diagnostic order
Before chasing this code directly, start with the basic system checks and follow a structured diagnostic approach. If other codes are present, do not treat U0122 as a stand-alone fault yet. Check what those codes mean first, then come back to this lost-communication code once the diagnostic order is clear.
Check the VSA side first
A key point on this one is that U0122 can store if the VSA modulator-control unit does not start normally. It can also store from a power or ground circuit problem at that unit. So before going deep into network diagnosis, make sure the VSA modulator-control unit power and ground side has been checked first.
Confirm the monitor condition
To reproduce the operating condition for the code, turn the vehicle to the ON mode, then wait for at least 6 seconds. During that window, if the body control module cannot receive the required data from the VSA modulator-control unit, it judges that communication as abnormal and stores U0122.
Keep network testing controlled
If the job moves into the broader B-CAN or F-CAN communication path, pause, recheck the earlier diagnostic path, and avoid guessing. Keep verification separate from the actual testing: confirm the vehicle can sit in the same ON-mode condition and that the code does not come right back. The takeaway is simple: prove the VSA unit can wake up and has its power and ground, then follow the communication path methodically. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0122 is best approached as a controlled communication diagnosis: check the VSA unit power and ground first, then follow the network path without jumping to conclusions.
For more guided automotive diagnostics, visit STEP Diagnostics.
