Powertrain, generic · Hybrid propulsion

P0AA1 Hybrid/EV Battery Positive Contactor Circuit Stuck Closed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

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

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

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–3,000
Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv battery positive contactorbmswiring harness

Related codes

P0AA2P0AA4P0AA0P0C76P0AE2

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