Network, generic (extended)
U352C High Voltage System Interlock Circuit H High
Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible
U352C reports an excessive reading on loop H. Whether that points to foreign voltage or to a break depends on the quantity the controller evaluates. If it reads voltage, a wire touching 12 V is the usual reason. If it works out the loop's resistance, as Lear's tester patent does, a value beyond the maximum is treated as open and one under the minimum as shorted, so high may mean corrosion or a loose terminal. The service data of the specific vehicle settles which reading applies; for U352C no maker publishes it. Measure loop H resistance with every plug latched and compare it with a sound loop of the same vehicle.
Likely causes
Loop H wire in contact with a 12 V supply
Corroded or loose terminal raising loop H resistance
Loop source stuck on in the controller
Symptoms
- No ready mode, high-voltage warning
- Fault sometimes disappears after moving connectors
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 hhvil wiring
Related codes
References: patents.google.com, law.cornell.edu.