Without physically looking under the van it could be tricky. (under the van there closer to the engine there should be the catalytic converter and a larger looking silencer - usually the dpf has smaller pipes running in and out.
Other than that do you know if your van is euro 4 or euro 5, I believe the euro 5 are all dpf equipped hence why they passed the emission regulation. (got me thinking now does it say euro 5 on a log book?)
Or another way is to find out how many grams of CO2 your vehicle emits surely the dpf will be lower?
Just my 2ps worth and I am sure someone will correct us soon!
I haven't looked at my DPF yet, but when this awful weather improves I might crawl under my van with a camera and take some pics. In the mean time, a google image search for nissan diesel particulate filter should give you an idea of what you are looking for- bulge in the exhaust pipe, fairly close to the engine, with small-bore pipes coming out of it for pressure sensor etc.
Not sure if CO2 figure would reveal much. I thought the DPF was a mechanical filter designed to trap solid particals. CO2, being a gas, would pass straight though? (I'm no expert though, and would gladly be corrected on this)
Hi Lads and a happy new year to you all, thanks for your replies. When I serviced it recently I noticed a large box in the exhaust very close to the manifold. It is about twice the diameter of the exhaust pipe but I failed to notice if any pipes or wires were attached. It could be a catalytic converter. I will have another look and let you know.