P0AA8Hybrid/EV Battery Voltage Isolation Sensor Circuit Range/Performance
- 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
- 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.
- What you may notice
- Check engine and hybrid or EV system warnings
- Reduced power or speed limit until restart
- Isolation monitoring unavailable, so related faults may go unreported
- Likely causes
- 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)
- 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.