Diagnostic article Generic OBD-II
P23B5: NOx sensor 3 heater resistance misses its target
P23B5 assesses the third NOx sensor heater resistance after extended supply and dewpoint 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.
P23B5 evaluates heater-sense performance for NOx sensor 3. It compares measured heater resistance with target resistance using a normalized difference. This is an operating-performance check, separate from the explicit open and short diagnoses for HTemp.
Delays are part of the test
The cited calibration requires more than 200 seconds after the sensor supply reaches its stated range above 10.8 V and more than 200 seconds after dewpoint. It also lists more than five seconds after overrun, valid communication and the appropriate combustion mode. The fault counter is 125 failures out of 250 samples at 25 ms intervals. Unlike the sensor-2 performance entry, this row is Type A, one trip.
The printed ±0.06 inequality presentation conflicts with the out-of-range narrative. It is therefore unsuitable as an unqualified workshop pass/fail formula.
What establishes a useful result
A brief warm-up or cold resistance reading cannot reproduce the qualified operating comparison. Review actual and target heater information where the vehicle exposes it, and establish that the lengthy prerequisites were satisfied. An unrun monitor is not a passing monitor. Obtain calibration-specific clarification for numerical limits before condemning hardware; this summary supports the comparison mechanism and timing but leaves the exact inequality unresolved.
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 1460.
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 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