Network, generic (extended)
U3546 High Voltage System Interlock Circuit P Performance
Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible
U3546 marks loop P as implausible. On large vehicles the mechanical routing of HV cables affects the interlock too. Gillig's field service campaign FSC 22-13-2479 for its Gen 2.0 and 2.5 battery electric buses found that HV battery cables in one equipment compartment lacked adequate support brackets; the outcome was an intermittent HVIL fault 8175, sometimes with the HV exposure lamp lit, and the fix was added bracketry. A heavy cable that swings with every bump can tug at its plug just enough to upset the loop for an instant. No maker documents U3546. Look for unsupported cable runs close to the plugs of loop P.
Likely causes
HV cable without adequate brackets pulling on a loop P plug
Loose contact in a loop P connector
Cable clamp or bracket not refitted after repair
Symptoms
- Interlock fault that comes and goes, more often on rough roads
- High-voltage warning lamp lighting briefly
- Brief loss of high-voltage power
Repair estimate
DifficultyHardWorkshop job
Parts and labour€80–1,200
Time1–4 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
hvil loop p
Related codes
References: static.nhtsa.gov, law.cornell.edu.