P0AA7Hybrid/EV Battery Voltage Isolation Sensor Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyFailed isolation bias switch or measuring circuit inside the battery controller
- PossibleController software misreading electrical noise (update available on some models)
- RareOpen or loose isolation sense lead or connector at the battery
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.