OBD-II code · Powertrain (generic)
P0AA9 Hybrid/EV Battery Voltage Isolation Sensor Circuit Low
The ECM detects a circuit low fault on the hybrid/ev battery voltage isolation sensor circuit. Reading cannot be used reliably for control.
Is it safe to drive with P0AA9?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelySignal wire shorted to ground
- PossibleInternal sensor short
- Less likelyConnector pins corroded - high contact resistance
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 2–7 h
- Emissions test
- Usually unaffected
- Parts involved
- Hv Battery Voltage Isolation Sensor, Wiring Harness, Bms
Related codes
- P0AA6Hybrid Battery Voltage System Isolation Fault
- P0AA7Hybrid/EV Battery Voltage Isolation Sensor Circuit
- P0AA8Hybrid/EV Battery Voltage Isolation Sensor Circuit Range/Performance
- P0AAAHybrid/EV Battery Voltage Isolation Sensor Circuit High
- P0AABHybrid/EV Battery Voltage Isolation Sensor Circuit Intermittent/Erratic
- P0AACHybrid/EV Battery Pack Air Temperature Sensor A Circuit
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.