P0AA1: Hybrid/EV Battery Positive Contactor Circuit Stuck Closed
What to do
The car deciding not to restart after this stores is the system declining to run on half its safety disconnect — do not look for workarounds. Have it attended promptly, and if any workshop is going near the high-voltage system for other reasons, make sure they know this code is stored.
What this code means
The positive contactor stayed closed when commanded open — the weld the two-contactor design exists to survive.
How the car knows is worth understanding, because it explains when the code appears. At every shutdown the module opens the contactors and watches the voltage beyond them; voltage that stays present means a contact has welded. So this code is characteristically stored at switch-off, discovered rather than felt, and the car may then refuse the next start — not because it cannot run, but because it will not operate with half its disconnect gone.
What welds a contactor is arcing — contacts that have made and broken load current for years, or a closing sequence stressed by other faults. The remaining protection still works: the negative contactor isolates the pack alone. But a disconnect built with two locks is down to one, which is the U0151 argument — protection missing rather than harm occurring — and the reason this earns urgency without drama. It is also specifically a service hazard: anyone opening the system needs to know one contactor no longer answers commands.
Likely causes
Start here
- Welded battery contactor · specialist
Less common
- Wiring shorted to voltage · moderate
- Fault stored in the battery energy control module · 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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