Code Definition

P0AA4 — Hybrid battery negative contactor circuit stuck closed

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

About P0AA4

P0AA4 is a generic (obd-ii standard) powertrain diagnostic trouble code. 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 hybrid/EV control module commands the hybrid battery negative contactor to open, but the circuit remains closed. The system monitors the voltage on the high-voltage bus and expects it to drop when the contactor is opened. If voltage remains present or the contactor does not respond, the module identifies the contactor as being stuck closed.

Quick Facts