Powertrain, generic · Hybrid propulsion

P0AA8 Hybrid/EV Battery Voltage Isolation Sensor Circuit Range/Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Isolation measuring amplifier or reference in the battery controller out of tolerance
Pack voltage sense lead fault making the comparison value wrong
Controller software misreading electrical noise (update available on some models)

Symptoms

  • Check engine and hybrid or EV system warnings
  • Reduced power or speed limit until restart
  • Isolation monitoring unavailable, so related faults may go unreported

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

P0AA6P0AA7P0AA9P0AAAP0AAB

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