Network, generic (extended)

U3514 High Voltage System Interlock Circuit B High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3514 means loop B reads higher than allowed: a wire of the loop touches 12 V or another supply, or the loop does not fall back to its low state once the module turns its source off. GM's loop A code checks both states, allowing 24 % of 5 V while the source is off and 44 % while it is on. Ford's interlock patent tests the source line for a short to 12 V before releasing the loop, then stores a trouble code and turns on the Service Soon lamp rather than a general warning. In the reference design from Texas Instruments a short to battery shows up as loop current that no longer follows the commanded on/off pattern. No manufacturer lists U3514 itself. Disconnecting segments one at a time shows where the foreign voltage enters loop B.

Likely causes

Interlock wire of loop B shorted to 12 V or another supply
Interlock source in the module not switching off
Water in a connector bridging an interlock pin to a supply pin
Incorrect splice or add-on wiring after a repair

Symptoms

  • Vehicle will not start or enter ready mode
  • Service or HV warning lamp on
  • Fault stays present with all HV connectors properly mated

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 bhvil wiring

Related codes

U3511U3512U3513U3518P0A0D

References: patents.google.com, ti.com, gsi.ext.gm.com.