P0AA0: Hybrid/EV Battery Positive Contactor Circuit
What to do
If the car will not wake, check the twelve-volt battery before fearing the big one — contactors cannot close without it, and a tired small battery is the cheapest cause of a contactor code. Beyond that, this is the battery's disconnect system: qualified workshop only, no exceptions.
What this code means
The circuit monitoring the battery's positive contactor is reporting a fault.
The contactors are the pack's gatekeepers: two heavy relays, one in each pole, that physically connect the battery to the car when you press start and disconnect it when you stop — or crash. Both poles are switched deliberately, so that no single welded contact can leave the pack live, and the module watches each contactor's state through circuits like this one. The audible clunk from the back of a hybrid waking up is these closing.
This base code says the monitoring disagrees with the commanded state without yet claiming which stuck state (P0AA1 and P0AA2 do that). The suspects are the feedback wiring, the contactor's coil circuit, and the twelve-volt supply that drives it — contactors need a healthy twelve-volt system to close, which is why a failing small battery produces contactor codes on a perfect pack, the U0111 argument arriving at its most literal.
Likely causes
Start here
- Failing 12 volt battery · easy
- Open circuit in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- Faulty battery contactor · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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