P2A02: the third oxygen channel and its sensor-2 reference

P2A02 is described as bank 1 sensor 3 oxygen range/performance. In the cited table, the relevant channels are oxygen measurements associated with NOx sensors 3 and 2. The row specifies a full-load difference check with limits of +6% and −6%, rather than a simple electrical-voltage limit.

A chain of qualified comparisons

Sensor 3 and sensor 2 must both be fully operative. P2A01 must also be running, and the row qualifies the test using accumulated airflow after that diagnostic is enabled or disabled. This dependence makes sensor 2's health part of interpreting a sensor-3 complaint. The supporting fault list includes sensor-3 validity, pressure and signal-range checks, plus sensor-2 oxygen fault information.

The decision requires 121 failing observations from 240 samples at a 25-millisecond task interval. Engine operation and voltage above 11 volts are prerequisites. A single instantaneous separation between readings does not establish that this sampled comparison failed.

Useful diagnostic evidence

Capture the two oxygen channels together with their ready/valid states and P2A01's status. A discrepancy with a valid reference is different from one observed during reference-sensor warm-up or an inhibited comparison. Investigate the reference chain before interpreting P2A02 as proof that the third physical sensor needs replacement.

The extract does not fully spell out its A/B symbols in the strategy column, so this article does not extend its numerical difference into an unsupported wiring test. Verification requires the qualified comparison to run and remain within its bounds; ordinary engine operation alone is insufficient.

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 1529.