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U3547 High Voltage System Interlock Circuit P Low

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3547 reports a low value on loop P, and the contactors drop out with it. A design flaw can be the cause too. Kenworth (campaign 25KWC) and Peterbilt (25PBC) recalled battery electric T680E, 520EV and 579EV trucks under NHTSA number 25V181: with certain HVIL circuit layouts in their Accelera power control accessory subsystem, high voltage could be lost and the contactors open without warning, cutting propulsion. The remedy pairs a software check with two overlay harnesses. If a commercial vehicle keeps losing power on loop P, ask for open campaigns before hunting for wiring faults. No maker documents U3547.

Likely causes

Interlock circuit layout covered by a recall, overlay harness not yet fitted
Plug in loop P open or interlock pin pushed back
Loop P wire shorted to ground

Symptoms

  • Sudden loss of propulsion while driving
  • Contactors open without prior warning
  • No restart until the loop reads normal

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–1,500
Time1–4 h

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

Parts involved

hvil loop phvil wiring

Related codes

U3545U3546U3548U3543P0A0C

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.