P0AA1: Hybrid/EV Battery Positive Contactor Circuit Stuck Closed

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.

Symptoms

• 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

Most likely causes

• Positive contactor contacts welded, e.g. after high current or arcing
• Battery or hybrid controller software (GM Volt 2019, Jeep 4xe updates)
• Faulty battery disconnect unit (GM Bolt EV bulletin)
• Bus voltage sensing error making an open contactor look closed

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Use the scanner to command the movement and compare the actual position with the requested one.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

Good to know

• It can trigger limp mode.
• It affects emissions.

What each character of P0AA1 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• A: Hybrid or air and fuel
• A1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0AA1?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0AA1?

The most common causes are: positive contactor contacts welded, e.g. after high current or arcing; battery or hybrid controller software (GM Volt 2019, Jeep 4xe updates); faulty battery disconnect unit (GM Bolt EV bulletin).

Related codes

• P0AA2Hybrid/EV Battery Positive Contactor Circuit Stuck Open
• P0AA4Hybrid/EV Battery Negative Contactor Circuit Stuck Closed
• P0AA0Hybrid/EV Battery Positive Contactor Circuit
• P0C76Hybrid/EV Battery System Discharge Time Too Long
• P0AE2Hybrid/EV Battery Precharge Contactor Circuit Stuck Closed

Sources

• gsi.ext.gm.com: 19OBDG02 Hybrid Diagnostics
• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• static.nhtsa.gov: MC 10139138 9999
• static.nhtsa.gov: MC 10171419 9999

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.