P2201: NOx sensor 1 internal current-control stability

P2201 is a range/performance code for the engine-out NOx sensor in the reviewed GM system. The actual monitor checks embedded current-control stability, using separate NOx and lambda stability flags. It is not simply a test for a high or low reported NOx concentration.

Internal regulation must remain stable

The source describes stability decisions based on internal voltage and pump-current behavior. It then evaluates the proportion of time each stability flag is off. The monitor uses two failing samples out of two on a 12.5-millisecond task, but the flags themselves embody their own internal conditions. That task period is not a complete sensor warm-up time.

This distinction matters when the displayed NOx concentration appears plausible. A credible-looking concentration snapshot does not prove the sensor's internal control was stable throughout the observation period.

Several gates protect the comparison

The powertrain-relay voltage must exceed 11 volts and sensor supply exceed 9.90 volts, with the bus relay commanded on and CAN data valid. Dewpoint must be reached, the engine running outside cranking, and the heater must have remained within its target-resistance band for more than 10 seconds.

The fuel-request derivative also has to remain within its permitted range for more than five seconds. This separates the intended stable test opportunity from abrupt operating changes.

Verification should confirm those gates and review both internal stability results. The table lists Type B, two-trip reporting but no replacement verdict. Exact sensor hardware, vehicle applicability and any internal-status interpretation require the applicable 2025 GM service information.

Source: GM monitor, PDF page 1407.