Coil light flashing

Just want to make sure we are talking about the same light. Take a look at this picture and tell me if that is the light you are seeing.

If so, this could be as simple as a DPF sensor not reading properly. It is odd that there are no codes but the DPF sensors are simply measure the pressure difference before and after the DPF. This will tell the control module how full the DPF is. Basically when the pressure difference goes up (more pressure upstream then downstream) the more full the DPF is.

So the fact that you have a negative pressure at idle does not make much sense. How can you have less pressure in front of the DPF then behind it?

Unfortunately we don't have a manual on this vehicle because it is not offered in the USA, so we cannot offer much more info then general operation. However, we have these systems in the USA as well and they operate the same.

Let's start with this and go from there. Thanks

Hi KaseKenny1,

Many thanks for your reply. I can confirm that we are talking about the same coil light (as given in the image in your post).

The DPF pressure sensor on my car (image attached) has two inputs but only one of them (the long input) is connected to the DPF; the other (the short input) measures atmospheric pressure. Hence, in my case, the DPF pressure sensor is measuring the pressure inside the DPF relative to atmospheric pressure. The readings of this DPF pressure sensor that I quoted in the previous post were from a new pressure sensor that was fitted after the coil light started flashing (based on advice from my mechanic).

After reading forums, I have understood that the ECU computes soot levels using two methods - the measured method - where the ECU computes soot levels based on differential pressure i.e. based on the readings of the DPF pressure sensor and the other method - the calculated method - is where the ECU calculates the soot level based on parameters (other than the differential pressure) such as, maybe, miles driven, fuel consumed, lambda sensor readings etc.

First of all, is this two method determination of soot levels which I have explained correct?

Secondly, if it is correct, how does the ECU know when to base soot level determination on the measured method instead of the calculated method?

Okay. Our systems differ a little bit but this type of DPF sensor is used on other types of systems. So the way it calculates the soot level is actually a combination or both methods. Basically they are a check on each other. The vehicle runs a calculation on how much soot it should be producing and then it measures the soot load based on this sensor. They work very much like a check and balance. This way it will set some codes if they are not lining up with each other.

This is the way the systems work here so I am sure this part of the system is no different over there. It is pretty standard. It is called redundancy which will cut down on a vehicle running too long with faulty DPF system.

Many thanks for your reply.

With the 'measured' way (based on dpf differential pressure readings), soot levels can go down if the car is run at motorway speeds because this causes soot to burn and results in the dpf differential pressure going down. However, with the 'calculated' method, soot levels will always rise. Is that right? If not, what would one have to do to the car to make sure that the 'calculated' soot level drops.

Not necessarily but the reason it goes down on motorways is because the PCM will actually see the engine/vehicle speed and it will go into regeneration mode. The soot levels will actually always go up because soot is the by product of the combustion process. So the only way it will go down is through the regeneration process where the soot is actually burned to ash as you state. This is normally only done while driving on the highways/motorways because the exhaust has to get really hot and they don't want that done while driving slowly.

Hopefully that makes sense.