The diesel particulate filter: signs, regeneration, codes
The diesel got sluggish, consumption is up, the fan roars when parked. Here is what is happening and how to help.
The diesel particulate filter (DPF) sits in the exhaust and traps soot. The soot builds up and from time to time the unit burns it off — that is regeneration. While regenerations complete, the filter lasts a long time. Once they stop completing, everything else begins.
Signs of a clogging filter
- Loss of power, the car «will not go» — limp mode from exhaust pressure.
- Consumption up with no other reason.
- The cooling fan running while parked, heat coming from underneath: a regeneration is in progress.
- Rising oil level. Fuel used for the burn-off gets into the oil — with frequent unfinished regenerations that is dangerous in itself.
- A burnt smell after stopping.
What to look at in the data
- Exhaust pressure. Rising means the filter is clogging.
- DPF temperature. 600 °C and above during a regeneration is normal operation, not overheating.
- Codes P2002, P242F and their relatives speak about the filter directly.
Why regeneration does not finish
Town driving in short trips. A regeneration needs twenty minutes of continuous running on a warm engine — on a home-shop-home route it starts and is interrupted, and the soot stays.
Hence the cheapest way to help: drive half an hour on the motorway above two thousand rpm without switching off. Often that is enough.
What not to do
Cut the filter out. Legality aside, it changes the whole logic of the control unit: without pressure feedback it keeps injecting fuel for the burn-off, and at an emissions test it shows immediately.
Leave it to the last. A clogged filter can sometimes be cleaned on the car, more often it is removed and washed, and in a neglected case replaced entirely. The difference between the first and the third is an order of magnitude in price.
