P242F: Particulate Filter Restriction - Ash Accumulation Bank 1
What to do
This is one of the few particulate filter codes where a long motorway drive genuinely will not help. The blockage is ash rather than soot, and ash does not burn — so the usual advice to take the car for a sustained run does not apply here.
Expect the conversation to be about replacing or professionally cleaning the filter, which is a significant cost. It is worth getting a second opinion, because this code is occasionally set by a faulty pressure sensor rather than a genuinely full filter, and that is a much cheaper repair.
Ask whether the engine is using oil. If the filter has filled with ash sooner than the mileage suggests it should have, oil consumption is the usual reason — and a new filter fitted to an engine that is still burning oil will block again.
Be sceptical of any offer to remove the filter or empty it out. It is an emissions control device, removing it fails the MOT visually and on emissions, and it makes the car unlawful to use on the road.
What this code means
The particulate filter is blocked with ash, and ash is the one kind of blockage that regeneration cannot remove.
This is the most important distinction in the whole particulate filter family, and it is worth being precise about. A filter traps two different things. Soot is unburnt carbon, and it burns away during a regeneration. Ash is the incombustible residue left behind by engine oil additives, and nothing burns it. It simply accumulates, layer on layer, for the life of the filter.
So this code says the filter has reached the end of its service life rather than that it needs cleaning. The module has worked that out by noticing that the restriction no longer falls after a successful regeneration — the soot burned off, and the back pressure stayed high anyway.
Attempting more regenerations will not help, and forcing them does harm. Each one puts more fuel through the engine and more diesel into the oil, against a blockage that is not going to move.
The honest outcome is usually replacement or professional off-vehicle cleaning, where the filter is removed and the ash flushed or blown out. A filter that reaches this point unusually early is telling you something else is wrong — an engine consuming oil past worn bores or valve stem seals fills a filter with ash far faster than a healthy one, and replacing the filter without addressing that simply restarts the clock.
Likely causes
Start here
- Ash loading at end of filter life · specialist
Less common
- Engine burning oil into the exhaust · specialist
- Incorrect engine oil specification used · easy
- Faulty exhaust gas differential pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
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