Vauxhall Insignia with a blocked diesel particulate filter

In the workshop today:









Recently we had a vauxhall insignia in for repair with the engine management light on and blocked D.P.F. (Diesel particulate filter) symbol on dashboard. first we carried out a full diagnostic of the D.P.F. System and checked for fault codes. there were 2 codes present, P2453-5A diesel particulate pressure sensor signal not plausible and code P2455-11 particulate differential pressure sensor circuit high.

Most cars can come up with D.P.F. Pressure sensor faults when the D.P.F. filter is blocked. so the first code maybe just saying the D.P.F. Filter pressure is very high to the sensor as the D.P.F. is blocked. the second code also refers to the same D.P.F. Pressure sensor but is saying there is a fault in the electrical circuit. a D.P.F. Pressure sensor works by being connected to the exhaust before the D.P.F. Filter by a metal to rubber pipe. When the D.P.F. is starting to get blocked this causes back pressure to blow up the pipe which then the sensor reads the pressure is high and the vehicle initiates a D.P.F. Regeneration which then cleans the D.P.F. And lowers the back pressure again. If the D.P.F. Pressure sensor goes faulty then the vehicle does not know how the D.P.F. Condition is and will stop all regenerations.

So first of all we disconnect the D.P.F. pressure sensor from the pipe and we connect a mityvac to the pipe to read the actual physical pressure to see if the D.P.F. Is blocked, we start the engine and straight away the pressure is very high on idle, this indicates the D.P.F. Is very blocked as on idle a clean D.P.F. Should have virtually no back pressure.

Next we test the actual D.P.F. Sensor itself and test the wiring to the D.P.F. Pressure sensor. There are 3 pins which with the ignition on but engine off should read pin 1 5v feed pin2 earth pin 3 signal We tested pin 1 which had 5 volts. We tested pin 2 which had an earth, we then tested pin 3 (the signal wire which should read no more than .05 volts with the ignition on engine off if higher than .07v then the D.P.F. Pressure sensor needs to be replaced. Our car in question was reading 1.2v so the sensor was replaced.

Next we check the oil level as when a car is not regenerating properly this can cause the oil level to rise by having diesel wash into the sump from down the sides of the pistons, as when a car is trying to regenerate it fires the injectors on the exhaust stroke to heat up the D.P.F. Filter to raise the temperature to around 400-700 degrease, but if the car keeps trying to regenerate to often and keeps failing the oil level will rise and become diluted with diesel. our oil was ok so did not need changing on this vehicle.

Next we check the E.G.R. (Exhaust gas recirculation valve) on live data on the diagnostic making sure when the ignition is on and engine off it closes at 0%. As if the E.G.R. Is sticking open the vehicle will not get hot enough to regenerate. Next we test the glow plugs in the engine with a glow plug tester to make sure they are working as most cars with a D.P.F. Fitted will switch on the glow plugs when regenerating to raise the engine temperature. We tested them on this vehicle and 3 were found to be open circuit and not working and so were replaced. We also check there is power supplied to the glow plugs to power them when the vehicle is started (cold) this was ok.

So with our glow plugs fitted and new D.P.F. Pressure sensor fitted we clean the D.P.F. Using our very latest forte engine carbon cleaning machine. we connect the machine to the pressure pipe that feeds into the front of the D.P.F. And clean the D.P.F. By injecting the chemical with the forte machine into the D.P.F. Filter. This takes around 30 minutes.


Then we road test the vehicle, whilst having an assistant in the passenger seat with the diagnostic checking the D.P.F. Temperature sensors are reading ok and the D.P.F. Is now regenerating on its own. We then clear all the D.P.F. Adaptions and tell the vehicle that it has got a new D.P.F. Fitted (even though it is not a new one this resets all the readings and learned values for the vehicle). We take the vehicle for a further road test before giving the car back to the happy customer.

We get many customers asking us to clean there D.P.F. But we will not do this with out doing a diagnostic to test the D.P.F. system first, as in nearly all cases there is a reason the car will have got a blocked D.P.F. in the first place such as a faulty sensor, faulty glow plugs, blocked or sticking E.G.R. We have even seen cars that are not regenerating due to the coolant thermostat being faulty and not getting hot enough, Split turbo pipes or turbo leaks, faulty swirl flaps and many many more things.


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