Powertrain, generic · Hybrid propulsion

P0AA7 Hybrid/EV Battery Voltage Isolation Sensor Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

To measure isolation, the battery controller reads the voltage of each HV rail against chassis ground through an isolation sensor circuit and can switch in a known bias resistor. P0AA7 means this measuring circuit itself does not work, so the controller can no longer judge isolation. GM's 2016 and 2019 tables use it for a bias switch self-test: with all contactors open for 8 seconds after shutdown, switching the bias resistor must change both sensor readings; a combined change below 5 V squared sets the code, Type B, two trips. Mitsubishi lists P0AA7 to P0AA9 as leak detection circuit faults; on 2018 Outlander PHEVs noise caused false setting and a 60 km/h limit until restart, fixed by a sub-BMU update. P0AA6 is the actual insulation fault.

Likely causes

Failed isolation bias switch or measuring circuit inside the battery controller
Controller software misreading electrical noise (update available on some models)
Open or loose isolation sense lead or connector at the battery

Symptoms

  • Check engine and EV system service warnings
  • Power reduced or speed limited until the system is switched off and on
  • Regenerative braking warning on some models

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,500
Time0.5–4 h

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

Parts involved

hv battery voltage isolation sensorwiring harnessbms

Related codes

P0AA6P0AA8P0AA9P0AAAP0AAB

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