Exhaust and emissions
What is a particulate filter and how long does a regeneration take?
The diesel particulate filter (DPF) traps the soot in a diesel's exhaust, and many direct-injection gasoline engines have a similar one. It cleans itself by burning that soot in a regeneration, which usually needs several minutes of continuous driving at a steady speed; the exact time depends on the car and on how loaded the filter is.
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How does the filter clean itself?
With very hot exhaust, on the highway, part of the soot burns off by itself. When the filter is loaded, the control unit deliberately raises the exhaust temperature (active regeneration) for a while.
If the filter is too full, a workshop can force a regeneration with a diagnostic tool, following the manufacturer's procedure.
How long does a regeneration take, and how do I know it is happening?
Usually several minutes, and manufacturers explain in the manual how to help it: for example, driving for a while at a steady speed in a gear that keeps medium rpm. There is no figure that applies to every car.
Many cars give no notice. Clues: the fan running after you switch off, a higher idle, a hot smell or stop-start not working.
What happens if it is interrupted?
If you switch off halfway, the regeneration is left incomplete and will be repeated. Once is not serious; every time is: the filter fills up and its warning light comes on.
Also, frequent regenerations can let some diesel into the oil, which is why these engines need the low-ash oil the manufacturer specifies.
When should I go to a workshop?
If the filter light comes on and does not go off after the drive the manual describes, if the car loses power or if the check engine light comes on. Removing the filter is not allowed and the car will fail inspection.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P2002Particulate filter (bank 1): efficiency below threshold
- P2463Particulate filter: restriction - soot accumulation (bank 1)
- P242FParticulate filter: restriction - ash accumulation (bank 1)
- P2452Particulate filter pressure sensor A, circuit: malfunction
- P2458Particulate filter regeneration duration (bank 1): malfunction
- P2459Particulate filter regeneration frequency (bank 1): malfunction
Related symptoms
- Diesel particulate filter (DPF) warning light: what to do
- Particulate filter regenerating too often: causes
- Car loses power: what limp mode is
Learn more
See what your car is saying
With the ECO-LITE, your workshop can see the filter's codes remotely and, if the car publishes them, the soot load and the differential pressure.
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Frequently asked questions
Do gasoline cars have a particulate filter?
Many recent direct-injection gasoline cars do; it is usually called a GPF or OPF.
Is it bad to drive a diesel only on short trips?
It makes regeneration harder. Every so often, include a longer trip at a steady speed.
Can the filter be cleaned instead of replaced?
Often yes, with a forced regeneration or a workshop cleaning, depending on how much ash it holds.