P24AF: Particulate Matter Sensor Circuit Range/Performance
What to do
Ask whether a heater fault is stored alongside this code. If it is, that is very likely the real problem — this sensor cleans itself with a built-in heater, and one that is not working properly makes the sensor read nonsense.
Mention if the car burns oil or has had a coolant leak. Either can foul this sensor, and replacing it without addressing that leads to the same fault again.
The car will drive normally, so this is not urgent in the sense of being unsafe — but it is an emissions monitor, so leave enough time before an MOT for it to be fixed and for the car to complete its self-checks.
What this code means
The particulate matter sensor is producing a signal that is electrically valid but does not make sense.
Range/performance is the hardest of this family to diagnose and the most likely to be a genuine sensor failure. There is no open circuit and no short — the sensor is reporting a number, and the number is not credible.
The classic pattern is a sensor that never accumulates. It should slowly collect soot between regenerations, so its reading should drift in a predictable direction and then reset when the heater fires. A signal that sits flat forever, or one that jumps in a way soot accumulation physically cannot, is what sets this code.
Two mechanical explanations are worth ruling out before the sensor is condemned.
- The tip may be fouled with something other than soot. Oil or coolant reaching the exhaust coats the electrodes and stops them behaving predictably.
- The sensor may be in the wrong gas. After exhaust work, a sensor that sits in a pocket rather than the main stream sees very little of what is actually flowing.
A sensor whose self-regeneration heater is weak also lands here, because it never fully cleans itself and its baseline creeps. Check for a heater code alongside — if one is present, fix that first, because this code is then a consequence rather than a fault.
Likely causes
Start here
- Faulty particulate matter sensor · moderate
- Sensor drifted out of calibration · moderate
Less common
- Oil or coolant contamination on the sensor tip · specialist
- Sensor incorrectly positioned after repair · easy
- Exhaust leak upstream of the sensor · moderate
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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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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