Network, generic (extended)

U3530 High Voltage System Interlock Circuit J High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3530 flags loop J above its upper threshold. Foreign voltage is one explanation, but in a design that pushes a constant current through the loop and reads the drop across it, any added resistance lifts the measured value too. Tesla's HVIL tech note for early Model S cars, filed with NHTSA, names a poor solder joint at a charger board connector that exceeded 90 ohms only when hot. To reproduce it, technicians drove about 20 minutes at highway speed, charged for at least half an hour and measured the loop pins on the still warm charger. A loop J fault that turns up only after long trips or charging sessions points to such heat-sensitive joints. No maker documents U3530 itself.

Likely causes

Cracked solder joint or crimp in loop J whose resistance rises when warm
Loop J wire in contact with a 12 V supply
Loose or spread terminal in a loop J connector

Symptoms

  • Fault appears after long drives or charging, not on a cold start
  • Charging session or drive interrupted by a high-voltage warning
  • Loop measures normal once the components have cooled down

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,000
Time1–5 h

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

Parts involved

hvil loop jhvil wiring

Related codes

U352DU352EU352FU352CP0A0D

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