Network, generic (extended)
U351B High Voltage System Interlock Circuit D Low
Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible
U351B reports that too little level comes back from interlock loop D while the module drives it. GM's hybrid tables for the loop A code P0A0C give a frame of reference: the test only runs when on-board voltage exceeds 10.2 V, judges what fraction of a 5 V test signal returns against a 30 % limit and logs a Type A fault after two failed 12.5 ms readings. A weak 12 V battery thus pauses the check instead of tripping it. No maker publishes a calibration for U351B. Typical causes are a wire crushed against the body, a loop plug left off, or a dead source; the contactors behind loop D may not close.
Likely causes
Loop D wire pinched against the body and shorted to ground
Plug within loop D not seated after a repair
Test voltage source in the controller failed
Symptoms
- No ready mode or high-voltage branch D unavailable
- Warning to have the high-voltage system checked
- Fault stays present after clearing until the wiring is repaired
Repair estimate
DifficultyHardWorkshop job
Parts and labour€80–1,200
Time0.5–4 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
hvil loop dhvil wiring
Related codes
References: gsi.ext.gm.com, law.cornell.edu.