Powertrain, generic · Hybrid propulsion

P0A0C High Voltage System Interlock Circuit A Low

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

The voltage sensed on interlock loop A is too low while the module drives the loop – typically an opened loop or a short to ground. GM documents it codegenau: in its 2016 HPC2 table P0A0C sets when the sensed interlock voltage stays below 30 % of the 5 V test signal in 2 of 2 samples (12.5 ms each) with the 12 V supply above 10.2 V; it is Type A, so the MIL lights after one trip. The 2011 Volt tables used a 10 % threshold. Mercedes-Benz model line 243 stores P0A0C00 in the DC converter and on-board charger as a short to ground in the interlock circuit. The opposite fault is P0A0D. Since the loop guards against live HV parts, the system drops the contactors and the car will not drive on electric power.

Likely causes

HV connector, cover or service disconnect open, interrupting the loop
Interlock wire shorted to ground, e.g. chafed at a module or the body
Corroded or pushed-back interlock pins
Faulty interlock source or sense stage in the battery or hybrid module

Symptoms

  • Check engine light (GM Type A) and hybrid/EV warning
  • No ready mode, electric drive unavailable
  • Charging may be blocked

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

hv interlock loophv service connector

Related codes

P0A0AP0A0BP0A0DP0A0EP0D17

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.