P0AA5 code meaning
Hybrid/EV Battery Negative Contactor Circuit Stuck Open
Powertrain system Generic code P0Axx codes Check engine light
What P0AA5 means
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).
P0AA5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0AA5
- Vehicle does not start or reach ready mode
- Hybrid or high voltage battery warning
- Charging not possible
Common causes of P0AA5
- Most likelyOxidised contact surfaces after long standing or high humidity (Audi)
- PossibleFailed battery junction box or burnt negative contactor
- Less likelyContactor coil not energised due to wiring or 12 V supply fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery negative contactorBms
What each part of P0AA5 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A | Area: hybrid propulsion. |
| A5 | The exact fault in that area. |
What to do next
- Note P0AA5 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0AA5
What does P0AA5 mean?
P0AA5 means "Hybrid/EV Battery Negative Contactor Circuit Stuck Open". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0AA5?
Drive gently and only to a workshop. With P0AA5 the car can go into limp mode (reduced power) to protect itself.
Will P0AA5 fail an emissions test?
Yes, it can. P0AA5 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0AA5 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 6 hours of work. This is a job for a workshop.
Will P0AA5 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.