Service Issues: XC90 D5 engine DPF (Diesel Particulate Filter)

[shimon340]

hi there

sorry to hear of your problems with your filter on the xc90.

having worked on dpfs ( research dept ) I think I can help out here.

Basically, the diesel particulate filter ( dpf ) is effectively a fine mesh placed in the exhaust. It catches diesel particulates (soot). The filter is also coated with some metals which act as a catalyst to burn the soot. The catalyst lowers the temperature at which the carbon / soot combusts. This therefore removes the soot from the exhaust, lowers the vehicles particulate emissions and therefore allows compliance with Euro 4.

however, the filter is like a catalytic converter in that it is actually a blockage in effect in the exhaust. The engine has to "push" the exhaust gas through the filter and this increased engine load ie the engine has to work harder. Making the assumption (which most likely isnt true) that the engine control programme for Euro 3 and Euro 4 was identical, a Euro 4 vehicle would have lower engine output / power and higher fuel consumpion and higher CO2 emissions ( from the burnt soot ) but lower particulate, hydrocarbon emissions than a Euro 3 vehicle. Almost all manufacturers re-write the engine programs ( called maps ) for Euro 4 to improve engine output and therefore keep power and CO2 emissions the same. more often than not CO2 emissions will be a bit higher for a Euro 4 engine as one engine emission ( soot and HC hydrocarbon ) has been converted to another ie CO2.


The vehicle has a "back pressure sensor" mounted in the exhaust ahead of the dpf. This gives information on how "blocked" the filter is. The dpf has metals to catalyst the oxidation / burning of the soot but this temperature is still higher than the exhaust gas temperature at idle. Exhaust temperature increases with engine revs - idle gives the lowest temperature.

So, with todays dpfs it is 100% possible for vehicle use and driving style to mean that the filter doesnt regenerate sufficiently during everyday driving.
This is due to current dpf technology meaning that the "light off" or the temperature at which regeneration occurs is too high and the filter doesnt regenerate sufficiently during town driving. This affects all manufacturers.

Systems will lower light off temperatures are not currently on the market as they are not sufficiently durable and either fail a vehicle manufacturers testing programme or fail to meet the American emission standards which give a time lifespan of the filter over which time its efficiently must not drop below certain %.

So, your vehicle will regenerate its own diesel filter if the exhuast temperature is high enough.

Alternatively, there is a backup fitted.

When the back pressure sensor triggers the fact the filter is sufficiently blocked it should activate a "fuel rich" engine control map. This runs the engine richer than normal increasing exhaust temperature and regenerating the filter.

If the filter fails to clear, the back pressure will still be too high and then the warning message will appear. The filter then gets manually regenerated ie heat with a heat gun!!! by a dealer or drive the car above a certain rpm for 15 mins. Interesting, the Renault laguna manual states "if the regenerating message is displayed, please drive the vehicle above 40mph for 15 mins" interestingly, this vehicle is "illegal" on the island of Guensey since the max speed is 30mph!

Your xc90 manual should say what revs are needed for what time to regenerate the filter. BUT, on the volvo this is only a back up to the self regeration!

So, your car fail to regenerate itself. you may wish to get the back pressure sensor checked. it maybe failing to respond early enough to activate the regeneration.

The diesel engines in the S40 /V50 are Ford/Peugeot 2.0 units. Im not sure if they use a cerium based additive. This is basically a metal injected into the exhuast to act as a catalyst to burn off the particulate matter. Renault also use a cerium based additive.

I would be surprised if Volvo is doing this in the S40 but the system was inherited from Ford so they probably had the choice of "use this cerium additive or dont have any Euro 4 diesel engines in the S40 range!"

From my time at Volvo trucks, my research was to find non-toxic and non precious metal catalysts which could be used. Volvo was against cerium due to its high toxicity...and didnt want it being released from the vehicle exhaust

hope you xc90 is sorted soon!

Ps the note you have about "every refuelling". There has been a bit of chinese whispers with that message. They most likely mean after consumption of a whole tank of fuel the filter will need regenerating - if the system doesnt self regerate with the rich cycle. they dont mean after every time you top up the tank

hope that helps. please keep me posted

S