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U352A High Voltage System Interlock Circuit H Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U352A says the eighth loop is closed but its electrical values leave the calibrated band. In CATL's interlock patent the decision thresholds follow from the loop current, a sensing resistor and the impedance of every HV part in the chain. A long loop through many parts therefore has narrow margins: each extra contact, a replacement part with different internal resistance or a lengthened harness shifts the result. That makes a performance fault on a late loop plausible after repairs or conversions. No maker publishes U352A. Compare part numbers of recently fitted HV parts with the originals and look for added plugs in loop H.

Likely causes

Replacement HV component with different interlock resistance fitted
Extra connector or harness extension added to loop H
Rising contact resistance at several loop H terminals

Symptoms

  • Fault appears after a repair or conversion
  • High-voltage system switches off occasionally

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,000
Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hvil loop h

Related codes

U3529U352BU352CU3526P0A0B

References: patents.google.com, law.cornell.edu.