What P0AA7 means
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.
How the engine computer detects it
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 (37 mph) limit until restart, fixed by a sub-BMU update. P0AA6 is the actual insulation fault.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
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
Common causes
- Failed isolation bias switch or measuring circuit inside the battery controller Most likely
- Controller software misreading electrical noise (update available on some models) Possible
- Open or loose isolation sense lead or connector at the battery Less likely
How to diagnose P0AA7
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: hv battery voltage isolation sensor, wiring harness, bms.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- A
- Hybrid and electric propulsion
- A7
- Specific fault
Questions drivers ask
Can I drive with code P0AA7?
Have it checked before you drive further. An isolation fault means the high-voltage system may be leaking voltage to the car's body. Many hybrids and EVs limit or shut down the drive system. Never touch orange high-voltage cables, and leave the repair to a shop trained on hybrids.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.