Diagnostic article Generic OBD-II
P22A7: NOx sensor 2 heater resistance fails its performance check
P22A7 compares post-catalyst NOx sensor heater resistance with its target after several readiness delays.
Read before applying this article
Documented application
2025 GM 25OBDG04B diagnostic parameter file; the cited monitor is documented, but individual vehicle, engine and calibration applicability has not been established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P22A7 is a performance diagnosis for the heater-sense system of NOx sensor 2. The controller compares raw heater resistance with target resistance using a normalized difference. This differs from the explicit HTemp open, ground-short and power-short entries nearby.
A qualified resistance comparison
The row prints positive and negative 0.06 bounds, but their inequality presentation conflicts with its “out of range” description. Those signs should not be turned into a workshop pass/fail formula without calibration-specific clarification. The supported point is that actual heater resistance is assessed relative to its target.
The enable timing is clearer: a delay exceeding 45 seconds after supply is in range above 10.8 V, more than 180 seconds after dewpoint, and more than five seconds after overrun. The table also requires valid communication and applicable combustion mode. It lists 125 failures out of 250 samples on a 25 ms task and Type B, two-trip reporting.
What to verify
A cold resistance reading alone does not reproduce this operating performance test. Review target and actual heater behavior, if supported, after the qualifying delays and operating conditions. Also distinguish an incomplete monitor from a completed successful comparison. This source does not establish that every P22A7 requires a sensor replacement, and its ambiguous inequality prevents treating the printed numerical bounds as universal service limits.
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 1434.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
NOx Sensor Heater Sense Circuit Range/Performance Bank 1 Sensor 2
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT