I have a 09 diesel X Type and the DPF filter packed up last October and was replaced (free of charge) by the dealership. But the light ( amber) has been coming on again after about 10 miles but goes out after about another 10. I had it serviced last week (by ex Rolls Royce mechanics here in Edinburgh-much cheaper) and they say there is nothing to worry about but to take it for a long run;which is just what I am about to do.

Should I worry about this and why does it come on and go out ?

Any advice much appreciated.

Robert.

 

Robert, do you do a lot of short runs with your car (ie, under 20 KM)? If so, what you are experiencing is the DPF not having time to adequately clear out the DPF since it needs to get it very hot to convert the carbon to CO2. If you can do a run for say 100 KM or so, that would be ideal as this will allow the vehicle to get up to temp and then to get the DPF up to a temp that it needs to get to. If you can, also find a long grade to drive up with 3 of your friends in the car and accelerate up the hill. This will put a heavy load on the engine which will also help to raise the exhaust temps and burn the carbon out of the DPF. Granted, the computer will do most of what you need by simply driving the car.

As for why the DPF light goes in and out, what is happening is your DPF is getting full of carbon and the computer is sensing the backpressure and it is wanting to clean out the DPF. But, if you are not giving it a long drive in which to do this, the carbon will partially clear itself and then the next time you drive it, it will load back up with carbon due to running the engine slightly rich while it is not up to temp yet. The other possibility is that you have a leaky fuel injector and what is happening is one cylinder is running rich and it is causing it to carbon up the engine. Any mechanic should be able to do a bleed down test of the fuel system and see if that is good or not. That would be a fairly cheap test to do and tell you if your fuel system is in good condition.