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U3529 High Voltage System Interlock Circuit H

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3529 marks a fault on circuit H, the eighth interlock loop, without a more specific result. Texas Instruments distinguishes one central loop running through all high-voltage parts from individual loops inside each subsystem that confirm its own assembly. Eight separate loops are realistic mainly for trucks, buses and machines with several packs and distribution boxes, such as Volvo's electric-road trucks with at least two HV buses or Caterpillar's multi-pack machines; in passenger cars a fourth to eighth loop is hardly to be expected. No manufacturer documents U3529. On a car, compare codes in other units before assuming a wiring fault.

Likely causes

Connector or disconnect on loop H open
Loop H wiring damaged on chassis or between packs
Code logged by a controller with faulty software rather than a real loop H fault

Symptoms

  • One HV branch or pack unavailable, or no ready mode
  • Warning about the high-voltage system

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time0.5–5 h

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

Parts involved

hvil loop hhv connectors

Related codes

U352AU352BU352CU3525P0A0A

References: ti.com, patents.google.com, patents.google.com.