What is a DPF?
A diesel particulate filter (DPF) is a honeycomb-shaped ceramic filter fitted into the exhaust of most diesel cars. Diesel engines produce tiny soot particles as they burn fuel, and left alone those particles are harmful to breathe in. The DPF's job is to physically trap that soot inside its honeycomb structure before it can leave the exhaust pipe, rather than letting it out into the air.
DPFs became standard equipment on new diesel cars sold in the UK and Europe as emissions rules tightened, and today almost every diesel you'll come across on the road — from small hatchbacks to vans — has one fitted somewhere along the exhaust, usually close to the engine so it stays hot.
How the filter clears itself: regeneration
A filter that only ever trapped soot would block solid within a few hundred miles, so the DPF is designed to burn that soot off periodically in a process called regeneration. There are two ways this happens:
- Passive regeneration — on a longer motorway-speed run, the exhaust naturally gets hot enough (roughly 350–500°C) to burn the trapped soot off in the background, with the driver noticing nothing at all.
- Active regeneration — if the car has mostly done short, low-speed trips and the exhaust hasn't been hot enough on its own, the engine's computer steps in and deliberately raises the exhaust temperature — usually by injecting a little extra fuel — to force a burn-off. You might notice a slightly higher idle, a faint smell, or the cooling fan running after you've parked up.
Either way, the car's computer needs to know how much soot is actually sitting in the filter before it decides whether regeneration is needed. That's the pressure sensor's job.
What the DPF pressure sensor does
The DPF pressure sensor — sometimes called a differential pressure sensor — doesn't measure soot directly. Instead, it compares the exhaust pressure before the filter with the pressure after it, using two small sensing pipes that tap into the exhaust on either side of the DPF.
A clean filter lets exhaust gas pass through with very little resistance, so the pressure reading on both sides is similar. As soot builds up inside the honeycomb, it becomes harder for gas to pass through, and the pressure before the filter rises compared with the pressure after it. The bigger that difference — the "differential" — the more soot the computer assumes is trapped inside.
The engine's computer combines that pressure reading with other information it already has, such as engine speed, load and exhaust temperature, to build a picture of how full the filter really is, and decides whether it's time to trigger an active regeneration.
Signs the pressure sensor — or the filter itself — needs attention
Because the pressure sensor feeds the computer the information it uses to manage regeneration, a fault here can look a lot like a genuinely blocked filter, and it takes a proper diagnostic read to tell the two apart. Common symptoms include:
- The DPF warning light staying on, or the general engine warning light appearing alongside it
- The car going into "limp mode," with noticeably reduced power
- Regeneration cycles that keep failing, or that seem to happen far more often than they should
- Higher fuel consumption than usual
- Visible black or excessive smoke from the exhaust
When a car like this is plugged into a diagnostic reader, some of the generic fault codes that point at this sensor and its circuit include P2452, P2453, P2454 and P2455 (DPF pressure sensor circuit faults), and P244A and P244B (differential pressure reading too low or too high). Exactly what a code means varies a little by manufacturer, which is one reason a code on its own isn't the full story.
A very common cause of a "faulty" pressure reading isn't the sensor itself — it's the two small sampling pipes that run from the exhaust up to it. These can become blocked with soot or condensation over time, especially on cars that mostly do short journeys, and a blocked pipe sends the computer a false reading just as easily as a broken sensor does.
That's why a proper diagnosis reads the sensor's live data and checks the physical pipework, rather than reading the fault code off a scanner and reaching straight for a new part.
Is it legal to remove a DPF in the UK?
No. Removing or "deleting" a DPF breaches the Road Vehicles (Construction and Use) Regulations 1986, which make it an offence to use a vehicle on a public road if a fitted emissions control device has been removed or made inoperative. Since 2014, MOT testers have been required to visually inspect the DPF housing, and a filter that's been removed, bored out, or is missing is an automatic MOT failure with no way round it — a smoke test alone isn't enough.
On top of an MOT failure, driving a car with a deleted DPF on the road can carry a fine of up to £1,000 for a car (£2,500 for a heavier goods vehicle), and it can also invalidate your insurance if there's ever a claim. Chasing away a warning light by removing the filter tends to cost a lot more in the long run than dealing with the actual fault.
What we do about it
When a customer calls us about a DPF light, limp mode, or a failed regeneration, we start the same way we start every diagnostic job: with a fixed £75 call-out fee that covers proper diagnostic equipment and the first 30 minutes on site, at your home or workplace anywhere in Leeds or West Yorkshire. We read the actual fault codes and live sensor data rather than guessing from the warning light alone, check the sensing pipework for blockages before condemning the sensor, and — where the filter genuinely is the problem — talk you through a fixed price before any work starts.
You can see examples of recent diagnostic and repair jobs, including turbo and suspension work, on our portfolio page.
RELATED GUIDEWhat Does an EGR Valve Do — and Why Does It Cause Rough Idling?
The EGR is a different system to the DPF, but faults in one can affect readings from the other — here's how it works and what goes wrong.
Frequently asked questions
Can I keep driving with the DPF light on?
For a short while, yes, but it's worth getting it looked at soon. A car with a genuine DPF fault often can't complete a passive regeneration on its own, so the problem tends to get worse with time and mileage rather than better, and you risk the filter blocking solid.
How much does it cost to fix a DPF pressure sensor?
It depends entirely on what's actually wrong — a blocked sensing pipe is a cheap fix, while a replacement sensor or a genuinely blocked filter costs more. Our £75 call-out fee covers the diagnostic work needed to tell you exactly what's wrong and what it'll cost before you commit to anything.
Will a forced regeneration fix it?
Sometimes — if the filter is only lightly loaded and the sensor and pipework are sound, a forced regeneration can clear things up. If the underlying cause is a blocked sensing pipe or a failed sensor, though, a forced regeneration won't fix that fault and the warning is likely to come straight back.
Is a DPF delete a good way to avoid all this?
No — it's illegal to use on the road, it's an automatic MOT failure, it can invalidate your insurance, and it removes a filter that's there to stop harmful soot particles reaching the air you and everyone else is breathing.