Diagnostic article Generic OBD-II
P22A8: NOx sensor 2 heater-sense short to ground
P22A8 identifies a short-to-ground condition in the NOx sensor 2 heater-resistance measurement circuit.
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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.
The documented P22A8 failure is a short to ground at the HTemp heater-sense connection of the post-catalyst NOx sensor. HTemp supplies the heater-resistance measurement path. A low sense-circuit fault is therefore not interchangeable with P22A4, which concerns heater control.
Evidence the monitor uses
The sensor reports the ground-short category while the controller applies an 80-of-160 sample counter on a 25 ms task. Powertrain relay voltage must exceed 11 V, sensor supply must exceed 9.90 V, and the bus relay must be on. Dewpoint must have been reached. Communication loss and invalid CAN data are exclusions. The row specifies Type B, two trips.
The source notes internal 1.5-second electrical-fault debouncing for Continental generation 3.5 sensors. That is a stated sensor-family behavior, not proof that every platform will show the identical delay.
Diagnostic distinction
A plausible exhaust reading does not eliminate a heater feedback defect: concentration and heater-sense validity are separate observations. Conversely, an HTemp report does not establish which external terminal or internal component caused it. Use vehicle-specific circuit identification before any electrical testing. Confirmation should include a qualified, completed heater-sense check without the ground-short status. A scan immediately after clearing codes, before dewpoint qualification, leaves that question unanswered.
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 1435.
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 Low 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