P0AA1Hybrid/EV Battery Positive Contactor Circuit Stuck Closed
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P0AA1 means the positive main contactor conducts although it should be open, typically because its contacts have welded. GM checks this with all contactors commanded open for over 120 s (or the bus already below 9 % of pack voltage): more than 30 V on the positive bus in 4 of 6 samples sets Type B (two trips, 19OBDG02). Older GM programs test during precharge instead and set Type A after one trip if bus voltage exceeds 80 % (2011) or 60 % (2016) of pack voltage. GM bulletins cover the 2017 Bolt EV and welded contactors on the 2019 Volt; Jeep fixes false sets on the 2023 Grand Cherokee 4xe with software, Mitsubishi lists it as main contactor (+) seizure on the i-MiEV. The car may refuse to start.
- What you may notice
- Vehicle will not switch into ready or propulsion-active mode
- Check engine light and service high voltage system message
- Often stored together with P0AA4 or a slow discharge code such as P0C76
- Likely causes
- LikelyPositive contactor contacts welded, e.g. after high current or arcing
- PossibleBattery or hybrid controller software (GM Volt 2019, Jeep 4xe updates)
- PossibleFaulty battery disconnect unit (GM Bolt EV bulletin)
- RareBus voltage sensing error making an open contactor look closed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.