Diagnostic article Generic OBD-II
P0AA1: Battery contactor appears to remain conductive after opening
P0AA1 evaluates link-voltage behavior after a contactor-open command in the documented BAS hybrid system.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG08 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0AA1 is the contactor-stuck-closed check in GM's BAS hybrid summary. The controller compares link voltage before and after an open command under a qualified shutdown state. The concern is that the expected electrical separation has not occurred.
Voltage behavior needs the command and current context
The published criterion looks for link voltage remaining within 500 millivolts of its pre-opening value. The table also qualifies the check with a specified pack-current condition observed shortly after the open command, power mode off or accessory, and valid supporting diagnostics.
This is not a universal instruction to measure inside a battery pack. It explains why a contactor status bit alone is insufficient: the monitor checks electrical behavior associated with the commanded transition.
A stuck-closed report requires controlled service assessment
The source separates P0AA1 from the contactor control-circuit low and high codes. A control-feedback fault and failure to achieve electrical separation are related concerns but different monitored results. The code alone does not identify a particular welded contact or prove which component must be replaced.
Do not bypass the contactor or assume the system is de-energized because the command says open. Use the exact hybrid isolation and diagnostic procedures through qualified service. Verification must establish the prescribed electrical separation and completed monitoring after correction. Clearing the code cannot demonstrate that a contactor now opens safely.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG08 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Hybrid/EV Battery Positive Contactor Circuit Stuck Closed
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT