Code Definition

P0AA4 (232) — Hybrid battery negative contactor circuit stuck closed

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

About P0AA4

P0AA4 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 P0AA4 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 P0AA4 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

This DTC is set when the Battery ECU (part of the HV battery management system) detects that the negative contactor in the high-voltage battery pack remains closed when it should be open. The ECU monitors the state of contactors during system shutdown or isolation checks. If the battery voltage remains present on the HV output terminals after a command to open the negative contactor, and the condition persists beyond a calibrated time, this fault is triggered, indicating a failure in contactor control or feedback circuitry.

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