Code Definition

P0AA1 (231) — Hybrid battery positive contactor circuit stuck closed

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Toyota

About P0AA1

P0AA1 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Toyota vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0AA1 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0AA1 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

Subcode 231 indicates that the hybrid vehicle control ECU or battery ECU has detected—through secondary confirmation or timing logic—that the positive high-voltage contactor remains closed after being commanded open, with the fault distinguished from other subcodes by specific timing or redundant signal conditions. It confirms the contactor's failure to open using both direct and indirect feedback methods during system shutdown or isolation sequences.

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