Most DPF replacements follow the same pattern — but a handful of vehicles have well-documented quirks that catch out even experienced fitters. If your vehicle is below, read its note before ordering or fitting. The general procedures are in fitting a DPF and fitting a catalytic converter.
Vauxhall Zafira (diesel) — EGR valve first
The single most common cause of a blocked DPF on a Zafira is a faulty EGR valve. Trade practice when replacing a Zafira DPF is to renew the EGR valve, exhaust-gas temperature sensor and differential pressure sensor at the same time — main dealers widely follow the same policy, because an incorrectly diagnosed Zafira can block its new filter in as little as 50 miles. If the car has swirl flaps, check their operating rod too; when it drops off with wear, the DPF blocks.
Euro 5 and Euro 6 Fords (and several PSA/Fiat vans) — the fuel vaporiser
Euro 5/6 Fords, along with vans such as the Peugeot Boxer, Citroën Relay/Jumper and Fiat Ducato, use a fuel vaporiser in the downpipe — a small injector that sprays diesel into the hot exhaust to bring the DPF up to regeneration temperature. Sitting in that gas stream, the vaporiser eventually clogs or fails, regeneration quietly stops, and the DPF blocks. Typical stored codes are P246B (conditions incorrect for regeneration) and P244C (exhaust temperature too low).
- Quick test: disconnect the diesel supply pipe at the vaporiser and connect a vacuum tester to the vaporiser — if you can pull any appreciable vacuum, it’s blocked.
- Check the vaporiser’s fuse (engine-bay fuse box) — it’s known to fail randomly, and that alone stores a fault code and stops regeneration.
- Check the metering pump that feeds the vaporiser, and prime a new vaporiser correctly when fitted.
- Replace the vaporiser whenever the DPF is replaced — main-dealer policy on many of these vehicles, and cheap insurance against the new filter blocking in 200–400 miles.
BMW diesels — glow plugs and twin thermostats
Many BMW diesels will not initiate regeneration if the glow-plug system isn’t fully healthy — and the glow-plug controller often fails without storing a fault code. When one glow plug fails, replace all plugs and the controller together. Note also that many BMWs run two thermostats (main and EGR); both must work for the engine to reach regeneration temperature, and a lazy thermostat is a classic hidden cause of a repeatedly blocking DPF.
Honda CR-V / Accord diesel and Jaguar XJ/XF/S-Type diesel
These models have manufacturer service bulletins relating to DPF blocking and its treatment — if you’re working on one, check the relevant bulletin (or ask us) before condemning parts, as the prescribed fix includes software and service steps as well as hardware.
Parts with their own fitting guides
BM Catalysts publishes dedicated fitting booklets for a number of specific part numbers whose installation has caught fitters out — different length to the OE part, brackets supplied in the box, and similar surprises. Where one exists for a part you’re buying, we’ll say so on the product page; you can also email us with the part number and we’ll send the relevant guide.