Technical P2454 / DPF differential pressure sensor issues

[lycopersicum]

Hello everyone,

Last week I got a P2454 code right after starting to drive, and I could confirm that the DPF pressure sensor was toast, reading a constant 4600 or so mV. Kavlico brand.

I just got a replacement sensor from Hella and installed it. It works but the pressure reading is all over the place -- see attached graph.

If I blow into the rubber tube I can generate a steady signal, so I know it's not the sensor -- the issues has to be somewhere upstream of the rubber pipes. As the pressure sometimes goes below the value with the engine off I wonder if there could be a leak on the high pressure side of the DPF.

I noticed that the seam where the DPF meets the exhaust pipe from the engine is not quite flat (see attached photo). Looks like there is some flaky material at the interface.

Wondering if this could be the issue and if it could have caused the demise of the previous sensor? Any other ideas?

First graph is the old sensor, showing a range of 40mV at idle (ish)
Second graph is the new sensor at idle with more than 100mV variations
Third graph is giving a bit of gas in neutral with the new sensor.

 

[bugsymike]

Hello everyone,

Last week I got a P2454 code right after starting to drive, and I could confirm that the DPF pressure sensor was toast, reading a constant 4600 or so mV. Kavlico brand.

I just got a replacement sensor from Hella and installed it. It works but the pressure reading is all over the place -- see attached graph.

If I blow into the rubber tube I can generate a steady signal, so I know it's not the sensor -- the issues has to be somewhere upstream of the rubber pipes. As the pressure sometimes goes below the value with the engine off I wonder if there could be a leak on the high pressure side of the DPF.

I noticed that the seam where the DPF meets the exhaust pipe from the engine is not quite flat (see attached photo). Looks like there is some flaky material at the interface.

Wondering if this could be the issue and if it could have caused the demise of the previous sensor? Any other ideas?

First graph is the old sensor, showing a range of 40mV at idle (ish)
Second graph is the new sensor at idle with more than 100mV variations
Third graph is giving a bit of gas in neutral with the new sensor.

Personally I don't know what the readings should be, there is a slight darker colour at the flange, any chance it is soot, apart from when it just starts from cold once it has been running any soot escaping will have burnt off with the heat there, sometimes it is possible to see if some one revs engine a bit from cold whilst watching "safely underneath" or just out of range of the wheels?
Apart from that I spoke top a Fiat Motorhome mechanic a while ago and he mentioned that the DPF sensor was one of the most common problems on the Ducato vans, they would of course have used genuine DPF sensor though.

 

[lycopersicum]

I'll check for soot on that flange. I did a test drive today and while the van goes perfectly the new sensor is definitely doing something weird. Here's another comparison, first the old and then the new.

It really behaves as if there is a leak -- the peak values are normal, but it always comes back down immediately.

Is there supposed to be some kind of sealant on the sensor lines, either where the rubber tube meets the metal pipe or where the metal pipe screws into the DPF?

 

[bugsymike]

I'll check for soot on that flange. I did a test drive today and while the van goes perfectly the new sensor is definitely doing something weird. Here's another comparison, first the old and then the new.

It really behaves as if there is a leak -- the peak values are normal, but it always comes back down immediately.

Is there supposed to be some kind of sealant on the sensor lines, either where the rubber tube meets the metal pipe or where the metal pipe screws into the DPF?

Sorry I don't know any more re this, perhaps other Forum Members can help.

 

[lycopersicum]

Quick update -- I've flushed the sensor pipes and checked all the connections, nothing untowards there.

I have a new hypothesis though. I managed to obtain data at a higher sampling rate from the sensor and it's full of high frequency noise when the engine is on and the pipes connected. I imagine the pressure in the exhaust is inherently noisy, the OEM sensor had a low pass filter to deal with it, and the new one doesn't -- causing aliasing when the ECU reads out the voltage. I've ordered a Meat & Doria sensor to check, I'll keep you updated.

 

[lycopersicum]

Update: same noisy signal from the Meat&Doria and even worse, the REF and HI inputs seem to be flipped, voltage goes down instead of up when blowing into HI...

I notice that aside from the branding, the Meat&Doria and the Hella parts are strictly identical down to the tiniest injection molding marks.

So based on this observation I'll try to find one that exactly matches the (slightly different) shape of the Kavlico...