Network, generic (extended)
U351A High Voltage System Interlock Circuit D Performance
Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible
U351A says that loop D returns a signal, but not the one the module sent out. Many designs feed the loop with pulses rather than a steady level. In a Corun battery patent a microcontroller sends a 0 to 5 V square wave at 100 Hz with half on, half off through the interlock switches of pack, motor controller and vehicle controller, and treats the loop as sound only if frequency, on-time and amplitude return unchanged. A rounded, shifted or weakened pattern hints at contact resistance, moisture or coupled interference rather than a clean break. No maker documents U351A. High voltage may drop out without warning.
Likely causes
Corroded or worn interlock contacts adding resistance to loop D
Moisture in a low-voltage connector of the loop
Loop wiring routed too close to switching high-voltage cables
Signal input of the evaluating controller faulty
Symptoms
- Sudden loss of high-voltage power while driving or charging
- Fault appears after rain, washing or on rough roads
- Restart sometimes possible after switching off and on
Repair estimate
DifficultyHardWorkshop job
Parts and labour€100–1,500
Time1–5 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
hvil loop d
Related codes
References: patents.google.com, law.cornell.edu.