P22A3: open heater-control circuit reported by NOx sensor 2

The cited P22A3 diagnosis looks for an open circuit on the heater-control pin of NOx sensor 2, the post-catalyst sensor. That is a circuit-integrity finding. It is different from a heater that remains connected but cannot track its operating target.

Reporting conditions

The controller uses an 80-of-160 failure counter on a 25 ms task. Powertrain relay voltage must exceed 11 V, the NOx sensor bus relay must be commanded on, and sensor supply must exceed 9.90 V. Lost communication and invalid CAN data must not be present. The table lists Type A, one-trip reporting.

Unlike the adjacent short-to-ground and short-to-power heater-control entries, this row does not list a dewpoint-reached requirement. That difference matters when comparing fault timing: an open-load report need not wait for the same warm-up milestone as every related heater code.

Diagnosis and verification

Record whether the reported fault concerns heater control, heater sensing or sensor communication before following a vehicle-specific test. The source does not supply a connector pin number, resistance limit or evidence that the complete sensor always requires replacement. A useful verification includes restored valid communication and a completed heater-control circuit check under its enabled supply conditions. Merely observing an exhaust-temperature rise does not demonstrate electrical continuity at the monitored control pin.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 1430.