Diagnostic article Generic OBD-II
P23B4: NOx sensor 3 heater-resistance sensing circuit is open
P23B4 detects an open HTemp heater-sense path in the third NOx sensor.
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.
P23B4 is the heater-sense circuit code for NOx sensor 3. The GM description identifies an open load on HTemp, the connection used for heater-resistance measurement. It is not the same open circuit as the heater-control failure P23B1.
Feedback versus command
A controller can request heater operation while the resistance-feedback path is unavailable. For that reason, seeing an active heater command cannot establish that the HTemp circuit is intact. The monitored report must specifically concern the sense path.
The row uses an 80-of-160 sample counter with a 25 ms task and Type A, one-trip reporting. Bus relay on, sensor supply above 9.90 V, relay voltage above 11 V and valid communication qualify the check. The source additionally notes 1.5 seconds of internal electrical-fault debouncing for Continental generation 3.5 sensors.
Following up the report
Use the actual sensor generation and vehicle wiring information before applying a test. The sensor-family debounce statement should not be assumed to describe every installed unit. After diagnosis, confirm that the sense-circuit open-load status resolves under qualified communication and supply conditions. A normal exhaust-temperature trend or successful heater command supplies different evidence and does not independently verify the HTemp measurement path. The table contains no resistance threshold or component-replacement instruction.
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 1459.
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 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