P24D1: Particulate Matter Sensor Regeneration Incomplete
What to do
This is the sensor cleaning itself, not the particulate filter regenerating — a much smaller thing, and it is worth being clear about because the two get confused. Driving differently will not fix this one.
Ask whether a heater fault from the same sensor is stored, since that is the usual cause and one repair normally clears several codes together.
Have the battery and charging system checked if they have not been recently. The cleaning cycle draws real current, and a tired battery or a poor earth can stop it completing on an otherwise healthy sensor.
The car will drive normally. Allow time before an MOT, because the emissions self-checks will not complete while this is stored.
What this code means
The particulate matter sensor's self-cleaning cycle did not finish.
Note carefully which regeneration this is about. It is not the particulate filter's regeneration — it is the sensor's own, much smaller one. The sensor burns the soot off its electrodes with a built-in heater so it can start a fresh measurement, and this code says that burn was started and not completed.
The distinction matters because the two faults get confused constantly, and the repairs have nothing in common. A filter regeneration is about driving conditions and a filter full of soot; this is about a heater on a small sensor.
Three explanations cover almost all of these.
- The heater is weak or failing, so the electrodes never reach burn-off temperature. Look for a heater resistance or heater circuit code alongside.
- The supply voltage sagged during the burn, which needs meaningful current — a tired battery or a poor earth does it.
- The cycle was interrupted by the engine being switched off partway through, which is benign if occasional.
A sensor that cannot clean itself is a sensor that cannot measure again. Its electrodes stay bridged with conductive soot, so it reports a permanently high reading that means nothing — and that downstream nonsense often sets the codes people notice first.
Fix the heater and the rest of the family usually clears with it.
Likely causes
Start here
- Faulty particulate matter sensor · moderate
- Corroded or loose connector · easy
Less common
- Low system voltage · easy
- High resistance in sensor wiring · moderate
- Poor sensor ground connection · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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