Diagnostic article Generic OBD-II
P24B6: particulate sensor heater remains electrically active when off
P24B6 checks for unexpected voltage or current in the particulate sensor heater during its PWM off state.
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.
P24B6 diagnoses a short to power on the soot-sensor heater line. The distinctive evidence is electrical activity during PWM off time. The source lists heater output above 6 V, an active switch input in the off state, or off-state switch current between 0.5 A and 15 A as diagnostic alternatives.
Why command phase matters
Voltage or current that may be expected during an on pulse can be abnormal during an off pulse. A measurement averaged across both phases does not necessarily reproduce the monitor's off-state decision. This distinction is central to interpreting the generic heater-control-high label.
The ECM requires a commanded-on sensor bus relay, no relay fault, valid communication and no sensor-control-unit undervoltage fault. Reporting uses 25 consecutive failures or 24 failures out of 96 samples at 100 ms intervals. The entry is Type B, two trips.
Confirmation
Review the heater command phase and the sensor control unit's electrical status using the exact service procedure. Do not infer that the heater is physically too hot solely from this code. Verification should show that the off-state check completes without unintended electrical activity while supply and communication remain qualified. The table supplies internal thresholds but no universal connector pinout, direct-power test or component-replacement verdict.
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 1495.
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
Particulate Matter Sensor Heater Control Circuit High
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