Diagnostic article Generic OBD-II
P2A00: oxygen drift against a modeled concentration
P2A00 compares measured oxygen with an estimated concentration under qualified operating conditions in this GM calibration.
Read before applying this article
Documented application
Documented 2025 GM gm-2025-04b monitor only; vehicle, engine and controller applicability must be established separately.
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 generic P2A00 title refers to oxygen-sensor range/performance, but this GM implementation is specifically a drift check. The controller compares measured oxygen concentration with an estimated concentration when the model is considered sufficiently stable. The table describes this as a full-load comparison while its continuation also lists fuel-cut qualification details; those terms should not be generalized into a universal drive cycle.
The reference is a model
The documented difference is measured minus estimated oxygen. Failure occurs above 5.20% or below −3.25%, so the two directions do not share a symmetric tolerance. The decision uses 121 failing observations out of 240 samples at a 25-millisecond task interval. The table identifies the signal through NOx-sensor-1 oxygen variables, which is more specific than assuming a conventional switching oxygen sensor.
The monitor needs engine operation, supply voltage above 11 volts, a fully operative sensor and valid supporting signals. Listed fault exclusions include NOx-sensor validity and pressure faults, oxygen-signal checks, injector-leakage information, airflow and EGR-related validity. Its continuation also requires the estimated oxygen concentration to remain stable.
What changes the diagnostic direction
A disagreement can arise from the measured channel or from inputs influencing the reference model; the code alone does not decide which. Review supporting airflow, fuel and EGR validity before treating the oxygen difference as proof of sensor failure. Record the sign of the discrepancy because the permitted positive and negative differences differ.
Confirmation requires a valid model and a running monitor. An apparently plausible idle reading is not equivalent to passing this qualified comparison.
Source and applicability
Documented 2025 GM gm-2025-04b monitor only; vehicle, engine and controller applicability must be established separately. GM monitor table, PDF page 1526; GM monitor table, PDF page 1527.
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 1 Sensor 1
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