P0AA8 code meaning
Hybrid/EV Battery Voltage Isolation Sensor Circuit Range/Performance
Powertrain system Generic code P0Axx codes Check engine light
What P0AA8 means
The two isolation sensor readings, positive rail to ground and negative rail to ground, should together equal the total pack voltage. P0AA8 is the plausibility check of that relation. GM's 2016 and 2019 tables fail it when the sum of both readings differs from the measured battery voltage by more than 5 V in 40 of 50 samples, with the bias switch open, Type B, two trips. GM's 2013 table compares mid-pack sensors with the motor controller's voltage reading and allows 15 V. Mitsubishi groups P0AA8 with P0AA7 and P0AA9 as leak detection circuit faults, which on 2018 Outlander PHEVs were set falsely by noise. Unlike P0AA9 or P0AAA, the signal stays in range but is implausible; P0AA6 is a real insulation loss.
P0AA8 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P0AA8
- Check engine and hybrid or EV system warnings
- Reduced power or speed limit until restart
- Isolation monitoring unavailable, so related faults may go unreported
Common causes of P0AA8
- Most likelyIsolation measuring amplifier or reference in the battery controller out of tolerance
- PossiblePack voltage sense lead fault making the comparison value wrong
- PossibleController software misreading electrical noise (update available on some models)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery voltage isolation sensorWiring harnessBms
What each part of P0AA8 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A | Area: hybrid propulsion. |
| A8 | The exact fault in that area. |
What to do next
- Note P0AA8 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0AA8
What does P0AA8 mean?
P0AA8 means "Hybrid/EV Battery Voltage Isolation Sensor Circuit Range/Performance". The two isolation sensor readings, positive rail to ground and negative rail to ground, should together equal the total pack voltage. It is a generic code, so it means the same on every make.
Is it safe to drive with P0AA8?
Drive gently and only to a workshop. With P0AA8 the car can go into limp mode (reduced power) to protect itself.
Will P0AA8 fail an emissions test?
P0AA8 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0AA8 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P0AA8 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.