P0AA5Hybrid/EV Battery Negative Contactor Circuit Stuck Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P0AA5 is set when the negative main contactor stays open or fails to conduct after the controller has commanded it closed, so the negative side of the high-voltage bus never connects. Audi reports it, alone or with P0AA2, on the 2020-2022 Q5 e quattro and 2021-2022 A7 e quattro plug-in hybrids with a no-start complaint; the stated cause is oxidation of the contact surfaces in the battery junction box after very long standing or extreme humidity. Audi's procedure: several ignition cycles and an EV road test with many consumers on, and a new junction box only if the fault returns. GM includes P0AA5 among the Ultium EV high-voltage codes that require pack data retrieval. It is the counterpart of P0AA4 (welded contacts).
- What you may notice
- Vehicle does not start or reach ready mode
- Hybrid or high voltage battery warning
- Charging not possible
- Likely causes
- LikelyOxidised contact surfaces after long standing or high humidity (Audi)
- PossibleFailed battery junction box or burnt negative contactor
- RareContactor coil not energised due to wiring or 12 V supply fault
- 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: €100 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.