Diagnostic article Generic OBD-II
P2A04: Post-catalyst oxygen sensor fails an active response test
P2A04 checks whether Bank 2 Sensor 2 responds to commanded rich and lean fueling in the documented LS7 example.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG07 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.
The GM group 07 P2A04 entry explicitly concerns the LS7 application and Bank 2 Sensor 2, the post-catalyst oxygen sensor. The controller actively changes delivered fuel to determine whether the sensor can reach the required rich and lean response thresholds. A voltage remaining inside its normal electrical range can still fail this performance check.
The controller challenges the response
This is not simply a count of ordinary oxygen-sensor switching. The monitor uses a commanded rich or lean condition and accumulated airflow to judge whether the rear sensor responded adequately. A passive scan-tool trace taken during unrelated operation does not reproduce that challenge.
The continuation page lists closed-loop and operating prerequisites, purge handling and conditions that abort the test. An aborted test is not a pass, and its absence after a short drive does not demonstrate sensor recovery.
Printed threshold polarity needs exact calibration context
The table's numerical threshold presentation is not fully aligned with its description of failing to reach those thresholds. This article does not reverse the inequalities or provide a universal sensor-condemnation voltage. The applicable service procedure must resolve the numerical decision.
Preserve commanded fueling, rear-sensor response and monitor status. The code alone does not prove the sensor rather than another influence on exhaust response is responsible. Verification requires a completed qualified response test after correction, not merely an erased code or a plausible resting voltage.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG07 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.
GM diagnostic parameters, PDF page 131 · GM diagnostic parameters, PDF page 132.
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
O2 Sensor Circuit Range/Performance Bank 2 Sensor 2
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