Network, generic (extended)
U351C High Voltage System Interlock Circuit D High
Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible
U351C is stored when loop D carries more voltage than its present state allows. GM's high check for loop A, P0A0D, shows why both states are tested: with the source commanded to 0 V, more than 24 % of 5 V counts as a failure, five times in eight samples; with the source at 5 V the limit is 44 %, four times in six. A loop that fails to fall when its source switches off reveals foreign voltage even if it looks normal while fed. No maker lists U351C. Likely are a loop wire touching a 12 V feed, a source that no longer turns off, or a bad repair splice. Readiness is withheld until the loop is clean.
Likely causes
Loop D wire in contact with a 12 V supply line
Source driver in the controller no longer switches off
Earlier repair splice joined the loop to a wrong wire
Symptoms
- Vehicle does not reach ready mode
- Fault returns immediately after clearing
- Other 12 V consumers may show faults if a supply wire is involved
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.