P2202: NOx sensor 1 reports below its usable concentration range

P2202 is labeled NOx sensor circuit low, bank 1 sensor 1. In the reviewed GM implementation, the monitored quantity is the raw engine-out NOx concentration, not a published external signal-wire voltage. The failure threshold is below −90 ppm.

A negative out-of-range value is not low emissions evidence

The monitor checks whether the sensor's reported concentration has fallen outside its permitted lower range. It does not establish that combustion produced a physically negative NOx concentration or prove unusually effective emissions control. A raw out-of-range value is a sensor-data validity issue under this strategy.

The controller requires no current-control failure and no relevant electrical fault on sensor 1. CAN communication and frame validity must also be acceptable. Those prerequisites distinguish this concentration-range check from a separate electrical or communication diagnosis.

Qualification and verification

The bus relay must be commanded on, relay voltage exceed 11 volts and sensor supply exceed 9.90 volts. Dewpoint must be reached, the applicable combustion-mode flag enabled and fuel-quantity request above the printed −1 mm³ boundary. Qualification uses 100 failures within 200 samples at 25 milliseconds each; reporting is Type B over two trips.

Verification should review the raw concentration after the sensor becomes eligible, together with its electrical and current-control status. A missing P2202 while another fault inhibits the check is inconclusive. The source does not identify a replacement component or establish universal sensor location. Confirm the exact vehicle and NOx system before applying these monitor-specific criteria.

Source: GM monitor, PDF page 1408.