Network, generic (extended)

U3513 High Voltage System Interlock Circuit B Low

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3513 reports a signal on interlock loop B that stays below its lower limit while the loop is energised by the module. What that means depends on the circuit: where the module feeds a test voltage in and reads it back at the far end, an opened plug reads low just like a wire touching ground. GM's documented loop A gives a sense of scale: its low code sets when less than 30 % of its 5 V check voltage comes back in two 12.5 ms samples, Type A. Texas Instruments' reference design shows how a current-fed loop can tell both apart: a grounded wire makes the loop current vanish while the supply current rises, with an open loop both drop. No maker publishes U3513. The contactors stay open; check loop B for chafed wires and unplugged connectors.

Likely causes

Interlock wire of loop B chafed through to ground
Plug or cover in loop B open, read as low by the sensing circuit
Pushed-back interlock terminal without contact
Interlock source in the monitoring module not delivering its signal

Symptoms

  • No ready mode, HV contactors stay open
  • Hybrid or EV warning lamp, MIL depending on maker
  • Charging not possible

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

U3511U3512U3514U3517P0A0C

References: gsi.ext.gm.com, ti.com, law.cornell.edu.