What it means
Same as P24AE with the signal in plausible range yet not matching the engine model.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The particulate matter sensor measures soot downstream of the diesel particulate filter so the control module can assess filter performance and regeneration. P24AF means the sensor signal is electrically plausible but does not agree with the module's expected soot model. Contamination or sensor ageing can cause this mismatch, but wiring faults or an exhaust leak near the sensor can also distort the reading.
Common causes
Most likely first.
- Particulate-matter sensor contaminated or degraded
- Damaged wiring or poor connector contact
- Exhaust leak affecting sensor readings
- Faulty sensor power or ground circuit
Symptoms
- Check-engine light on
- Possible emissions warning
- Possible reduced engine power
How to diagnose it
- Record freeze-frame data and compare PM sensor readings with DPF soot estimates, regeneration history, and related exhaust codes.
- Inspect the exhaust joints upstream of the downstream PM sensor for leaks that could alter its reading.
- Check the sensor tip for deposits or damage and inspect its connector and wiring for poor contact, heat damage, or chafing.
- Verify sensor power and ground and check signal stability while gently moving the harness.
- If the exhaust and circuit are sound, test the PM sensor against the manufacturer's procedure before replacing it.
Common fixes
- Repair an exhaust leak near the downstream PM sensor.
- Repair a poor connector contact or heat-damaged sensor wire.
- Clean the sensor only if the manufacturer's service procedure permits it.
- Replace a contaminated or degraded PM sensor confirmed by testing.
Can I keep driving?
A short trip is generally reasonable if the engine runs normally, but avoid repeatedly postponing repair because inaccurate PM readings can interfere with DPF monitoring and emissions checks. Arrange diagnosis sooner if reduced power appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.