P24B1: Particulate Matter Sensor Circuit High
What to do
Ask for the connector under the car to be checked first, including that it is actually plugged in. A sensor left unplugged after exhaust or filter work sets exactly this code, and that is worth ruling out before anything is bought.
Mention any recent work underneath the vehicle, since a disturbed or unlatched connector is one of the commonest causes here.
The car will drive normally. The concern is the emissions monitor rather than driveability, so plan the repair around your MOT date rather than treating it as an emergency.
What this code means
The particulate matter sensor signal is above the highest voltage the circuit should ever produce.
A signal pinned high has two quite different explanations, and separating them is the whole job. Either the wire has shorted to a supply voltage, or the circuit is open and the module is seeing its own pull-up with nothing loading it.
Both look identical from inside the module, which is why this code cannot be diagnosed from the scan tool alone. Unplugging the sensor and measuring at the connector separates them in a couple of minutes — an open circuit and a short to power behave completely differently once the sensor is out of the loop.
Because the sensor sits under the vehicle, the mechanical causes are the usual ones for that location: a harness pulled apart by stone damage, a connector unlatched by a previous repair, or a terminal that has corroded until it no longer makes contact.
Do not overlook the trivial case. A sensor left unplugged after exhaust work sets exactly this code, and it is a genuinely frequent finding on a car that has just been in for something else.
A sensor whose element has failed open also lands here, so the part is a real possibility — just not the first one to check.
Likely causes
Start here
- Open circuit in sensor wiring · moderate
- Sensor left disconnected after previous work · easy
- Corroded or loose connector · easy
Less common
- Wiring shorted to voltage · moderate
- Faulty particulate matter sensor · 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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