P2A01: sensor 2 oxygen drift relative to sensor 1

P2A01 is a range/performance code, but the cited GM strategy gives it a specific reference: sensor 2 oxygen concentration is compared with sensor 1 oxygen concentration. This differs from assuming that the controller simply rejects an electrical voltage outside a fixed range.

The upstream reference must be usable

The measured difference is sensor 2 minus sensor 1. The documented failure bounds are above +6.00% or below −6.00%, with 121 failures out of 240 samples and a 25-millisecond task. Both sensor channels must be fully operative, engine operation is required and system voltage must exceed 11 volts.

P2A00's diagnostic must be running. The row also qualifies the comparison with air-mass accumulation around P2A00 enablement and disablement. That relationship matters: sensor 1 is not an unquestioned reference merely because it displays a number on a scan tool. Its own oxygen-performance status affects whether the sensor-2 comparison is meaningful.

Read both signals together

Review both oxygen channels at the event rather than examining sensor 2 in isolation. A difference that emerges only while one sensor is not fully operative has a different evidentiary value from a sustained separation with both channels qualified. The table excludes several sensor-validity, pressure and signal-range faults, including sensor-1 oxygen fault information.

The source uses oxygen values associated with the NOx sensor system; it does not establish a conventional narrowband voltage test. Verification should demonstrate agreement within the documented comparison while P2A00 and the sensor-2 monitor can run. A cleared code or a single matching pair of readings does not establish completion.

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 1528.