Network, generic (extended)

U3518 High Voltage System Interlock Circuit C High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3518 is stored when loop C reads above its upper limit, usually a loop wire shorted to 12 V, to the wire of another loop in a shared connector, or a source stage that no longer switches off. Volvo's two-loop patent couples loops only through a galvanically isolated relay, so foreign voltage from one loop is not meant to reach another; where wires of different loops share a connector, damage can still bridge them. Ford's patent stores a code and switches on its Service Soon lamp once an interlock circuit is shorted high, and Texas Instruments shows that the loop current then stops following the commanded pattern. No maker documents U3518. The HV system stays off; inspect connectors that carry interlock pins of several loops first.

Likely causes

Interlock wire of loop C shorted to 12 V
Loop C bridged to another loop's wire in a shared connector
Interlock source for loop C stuck on in the module

Symptoms

  • No ready mode despite all HV connectors being in place
  • Service or HV warning lamp lit
  • High codes for more than one interlock loop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,200
Time0.5–4 h

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

Parts involved

hvil loop chvil wiring

Related codes

U3515U3516U3517U3514P0A0D

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