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U3528 High Voltage System Interlock Circuit G High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3528 means something lifts loop G to a level the controller never expects from it. Texas Instruments notes that automotive interlocks, unlike industrial ones, must survive a short to the 12 V battery and to ground; its reference design feeds the loop through an intelligent switch on the supply side with current limiting and thermal shutdown. Such electronics may come through a short undamaged, whereas a simpler output stage can fail, and then the code returns even after the wiring is repaired because the driver now stays on. No manufacturer documents U3528. Remove the foreign voltage, clear the code and test again before replacing a controller.

Likely causes

Loop G wire shorted to the 12 V supply
Loop output stage damaged by an earlier short and stuck on
Moisture bridging pins in a loop G connector

Symptoms

  • No ready mode, high-voltage warning
  • Code persists after the harness repair

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,800
Time0.5–4 h

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

Parts involved

hvil loop ghvil wiring

Related codes

U3525U3526U3527U3524P0A0D

References: ti.com, law.cornell.edu.