Diagnostic article Generic OBD-II
P23B3: NOx sensor 3 heater control is shorted high
P23B3 detects a short-to-power report on the third NOx sensor heater-control pin.
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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.
P23B3 belongs to the heater-control circuit of the NOx sensor after the second catalyst. The source explicitly describes a power short at the control pin. This is a different failure mode from an open load, a ground short or an out-of-target heater resistance.
Fault recognition
The controller requires sensor supply above 9.90 V, relay voltage above 11 V and the bus relay commanded on. Dewpoint must be reached and CAN communication and data validity must be intact. Reporting uses 80 failed samples out of 160 on a 25 ms task, with Type B, two trips.
Because the criterion is a reported electrical condition, an unusually hot sensor is not sufficient evidence for this code. Conversely, an apparently normal concentration display does not disprove a control-pin fault.
A focused verification
Identify the control path and compare the recorded fault with the vehicle's circuit test. Do not confuse it with the HTemp sense circuit, which has its own high-voltage code P23B9. Confirm the result only after the sensor reaches the prerequisites and the heater-control check completes. A scan taken before dewpoint can leave the check untested. The source supports this distinction and timing, but does not provide an external probe specification or a universal failed-part conclusion.
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 1458.
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 Control Circuit High Bank 1 Sensor 3
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