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U351D High Voltage System Interlock Circuit E

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U351D covers a disturbed fifth interlock loop, circuit E, where the module cannot narrow the fault down. Five loops arise naturally if every protected housing gets its own circuit. A GM patent describes this: each high-voltage enclosure has a functional interlock tied to its access point, and the low-voltage signal inside only gets through while that opening is closed. Removing a cover is thus noticed by the circuit of that very housing. Which enclosure belongs to loop E is not published. Check covers, lids and their screws first, then the plugs of the housings involved; high voltage stays off until loop E is closed.

Likely causes

Cover of a high-voltage housing on loop E not fitted or not fully tightened
Interlock contact or bridge in the cover bent or broken
Loop E wiring damaged between housings
Evaluating controller faulty

Symptoms

  • No ready mode after work on a high-voltage component
  • High-voltage warning in the instrument cluster

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–1,500
Time0.5–4 h

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

Parts involved

hvil loop ehv connectors

Related codes

U351EU351FU3520U3519P0A0A

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