Blocked DPF on a Ford Transit Custom: symptoms, diagnosis and the fix

The Ford Transit Custom is one of the hardest-working vans on Devon's roads, and a blocked diesel particulate filter is one of the most common reasons one ends up off the road. A van stuck in limp mode with the DPF light on, doing short local drops all day, is a job we see most weeks.

This is a worked example of how that job goes: the symptoms, what the fault codes actually tell us, and why a proper clean beats an expensive replacement.

The symptoms

The driver reported the van had dropped into limp mode and would not rev past a certain point, with the DPF warning light on the dash and noticeably worse fuel economy over the previous few weeks. That combination almost always points at the DPF, but the warning light is a symptom, not a diagnosis.

What the fault codes mean

Two stored codes told the story:

• P2002 - diesel particulate filter efficiency below threshold. In plain terms, the filter is too restricted to do its job.
• P244B - DPF differential pressure too high. The sensor across the filter is seeing more back-pressure than it should.

Together these confirm a genuinely restricted filter rather than, say, a faulty pressure sensor reading high on a healthy DPF. That distinction matters, because it decides whether you need a clean or a sensor. This is exactly why we always diagnose before cleaning.

Why it blocked

Short, stop-start journeys are the usual culprit. A van that rarely gets a long, hot run never completes a passive regeneration, so soot builds up faster than it burns off. Over tens of thousands of miles that soot turns to ash, and ash does not burn away at all - it has to be physically removed.

The fix

Rather than quote for a replacement filter, which can run to several hundred pounds plus labour, we removed the DPF and gave it a full off-car clean on our cleaning machine. The filter was flow and weight tested before and after, so the result is measured, not guessed.

Refitted, we ran a forced regeneration and a short road test to confirm the system was happy and the codes stayed clear. The van went back to the owner the same day with the original, vehicle-matched filter restored.

How to avoid it coming back

If a van lives on short urban routes, the single best thing you can do is give it a proper motorway run once a week so it can regenerate. If that is not practical, periodic off-car cleaning is far cheaper than replacement and keeps emissions where they should be for the MOT.

If your Transit Custom is showing the same signs, get it looked at early - it is much easier to deal with before it reaches a hard limp mode. See our blocked DPF cleaning page or give us a call.