Network, generic (extended)

U3538 High Voltage System Interlock Circuit L High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3538 is stored when loop L overshoots its permitted maximum. In a constant-current loop that can be a contact problem rather than foreign voltage. Tesla's Model S tech note records its most frequent HVIL field failure as high-voltage plugs serving the cabin PTC heater, the heater for battery coolant and the A/C compressor harness whose interlock pins were too short: the supplier had changed the housing without lengthening the pins, and in the worst case male and female never met. Higher resistance raised the loop voltage until the fault set. Replacement plugs with longer pins carry a yellow dot. Comparable part revisions can matter on any loop L. No maker documents U3538; high voltage stays off.

Likely causes

Connector revision in loop L with interlock pins too short for reliable contact
Loop L wire in contact with a 12 V supply
Spread female terminal in a loop L connector

Symptoms

  • Vehicle does not become ready or switches off high voltage
  • Heating or air conditioning affected if their plugs are part of the loop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time1–5 h

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

Parts involved

hvil loop lhvil wiring

Related codes

U3535U3536U3537U3534P0A0D

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