P24B7: Particulate Matter Sensor Heater Resistance
What to do
This one usually does mean the sensor itself, rather than wiring — the module has measured the heating element and found it out of specification. It is still worth asking for the connector to be checked first, since corrosion there adds resistance and looks the same from the module's point of view.
Expect other faults from the same sensor to be stored alongside, and expect them to clear together, because a heater that cannot burn the sensor clean makes everything else it reports unreliable.
The car will drive normally. Time the repair around your MOT, since the emissions self-checks will not complete while this is stored.
What this code means
The measured resistance of the particulate matter sensor's heater is outside its expected range.
This is a more precise code than the heater circuit high and low pair, and it usually points at the sensor itself. The module is not reporting that the wire is shorted or open — it has measured the heater's actual resistance and found it wrong, which is a property of the element rather than of the harness.
A heater element ages by degrading, and degradation shows as resistance drift. Thousands of cycles from ambient to red heat gradually change the element, and once resistance moves far enough the module can no longer predict the temperature the heater will reach from the current it draws.
Temperature prediction is the point. The sensor has to burn its accumulated soot off completely and repeatably, and an element whose resistance has drifted either underheats — leaving residue that corrupts the next measurement — or overheats and shortens its own life further.
Harness resistance can still be the cause, and it is worth eliminating because it is cheaper. A corroded terminal adds resistance in series with the element, and the module cannot tell the difference between resistance in the wire and resistance in the heater.
So check the connector, then accept the sensor. Where the connector is clean and tight, this code is one of the more reliable indications that the part has genuinely reached the end of its life.
Likely causes
Start here
- Faulty particulate matter sensor · moderate
- High resistance in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- Heat damage to sensor or wiring · moderate
Rare
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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