P226D: Particulate Filter Deteriorated/Missing Substrate Bank 1
What to do
The car will probably drive completely normally, and that is exactly the problem. This code says the particulate filter may not be filtering — which is an MOT and legal issue rather than something you would ever feel.
Ask for the pressure sensor and its two small hoses to be checked first. They block with soot or split, and that produces this reading with a perfectly good filter — much the cheapest outcome.
If you bought this vehicle recently, take the code seriously. A filter that has been hollowed out and refitted is a known way of disguising a failed one before a sale, and it produces exactly this. It is an MOT failure and makes the car unlawful to use.
Ask for the filter to be inspected rather than judged from the code alone — the difference between a cracked substrate and a missing one matters, and both are visible to someone who looks.
What this code means
The particulate filter's internal structure has failed, or is not there at all.
This code exists because a particulate filter can stop filtering while looking completely normal from outside, and the vehicle needed a way to notice.
A filter works by forcing exhaust through porous ceramic walls. If that ceramic cracks, melts or is removed, gas passes straight through — the shell is intact, the pipework is unchanged, and nothing is audibly or visibly different.
The module detects it by absence. A working filter creates a measurable pressure difference across itself; a hollow one creates almost none. On vehicles with a particulate matter sensor downstream, that sensor confirms it directly by seeing soot that should have been trapped.
Three situations produce it, and they are worth separating because two are innocent:
- A cracked or melted substrate, usually from a regeneration that ran too hot — which is what makes the over-temperature codes elsewhere in this corpus matter.
- A pressure sensor or its hoses at fault, in which case the filter is fine and the measurement is wrong. Check the hoses before anything else; they block with soot and split.
- A filter that has been deliberately gutted or removed. This is a known practice on used vehicles, and the shell is often refitted so it passes a glance.
That last case matters if you have bought the car recently. It is an MOT failure on emissions and on visual inspection, and it makes the vehicle unlawful to use on the road. A garage can tell by looking; you cannot.
Likely causes
Start here
Less common
- Particulate filter removed or hollowed out · specialist
- Genuine exhaust over-temperature during regeneration · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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