P24B5: Particulate Matter Sensor Heater Control Circuit Low
What to do
Ask whether other faults from the same sensor are stored, because this one usually explains them. The heater is how this sensor cleans itself between measurements, so when it fails the sensor stops reading correctly too — and both codes normally clear with one repair.
Ask for the connector to be examined for heat damage. This circuit carries real current, so a poor connection here burns rather than merely corroding, and a scorched connector needs replacing rather than cleaning.
The car will drive normally. Plan the repair around your MOT rather than treating it as urgent, since the emissions self-checks will not complete until it is fixed.
What this code means
The heater control circuit for the particulate matter sensor is sitting lower than commanded.
The heater is not a warm-up device here, and understanding that makes this code make sense. This sensor works by letting soot bridge two electrodes. Once bridged, it has to be burned clean before it can measure again — so the heater is how the sensor resets itself, and without it the sensor measures once and then stops working entirely.
A control circuit reading low points at a short to ground, a failed driver inside the module, or a heater element that has gone short-circuit. All three pull the line down, and the usual separation applies: unplug the sensor and see whether the circuit recovers.
Heater circuits carry meaningful current, which changes what fails. A signal wire tolerates a slightly corroded terminal; a heater circuit through the same terminal heats it, oxidises it further, and eventually burns it. So inspect the connector for discolouration and melted plastic rather than just continuity.
Expect a sensor performance code alongside this one, and treat the heater as the cause. A sensor that cannot self-clean reports nonsense within one cycle, so fixing this often clears both.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Faulty particulate matter sensor · moderate
Less common
- Corroded or loose connector · easy
- Heat damage to wiring insulation · moderate
Rare
- Failed control module output driver · specialist
Symptoms
Components involved
Information, not instruction
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