P0AA5: Hybrid/EV Battery Negative Contactor Circuit Stuck Open
What to do
As P0AA2 — small battery first, service plug second, expensive conclusions last.
What this code means
The negative contactor did not close when commanded — P0AA2's failure on the other pole, with the identical presentation (no READY, twelve-volt systems normal) and the identical cheapest-first list: twelve-volt battery, service plug, coil wiring, then the contactor.
Likely causes
Start here
- Failing 12 volt battery · easy
Less common
- High voltage service plug not fully seated · easy
- Open circuit in control wiring · moderate
- Faulty battery contactor · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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