[Rawediag]

Hi, guys. Friend of mine got strange reading on e90 320d n47. There was problem with DPF and backpressure sensor. He changed both with new oem parts, done service function DPF replacement. But backpressure reading fluctuate between 0-8 mbar, even with engine off! He measured 5V supply to sensor, ok. Tried different sensor, same. Changed DDE, 0mbar until he started, then 0-8, even with engine off. There is one fault in DDE -fuel heater activation. He changed it too, error is still there.Could there be some relation. Thanks for the answers.

[Node]

So what is your problem exactly?

[Rawediag]

Backpressure sensor value varies(jumping between 0-8mbar) with stopped engine.

[Node]

If its only 0 or 8 then I don't see any problem with that at all. Its probably 1 bit difference due to low resolution of ADC. So if real pressure (or sensor precision) is for example 4mbar then it will measure as 0 sometimes and 8 other times. You must understand this is not precision instrument with 5-6 decimals precision. Its made to get approximate backpressure reading.

[Rawediag]

Thanks for response, that makes sense. Error with fuel heater is 4b1b, but maybe that is for another topic. I know there was recall about fuel heaters, but this is 2007. I will check wiring when the car arrives.

[mr_nitroz]

I suppose you deleted engine adaptations. If not I would try it.

[Rawediag]

Yes he resets adaptations. Got some new info, the problem is backpressure jumping up to 13mbar. So it is not 4 or 8, but anything between 0 and 13, even with stopped engine. It is e87 lci 120d 4/2007 dde7.1 . There must be some interference, because he tried it with other dde and same behavior.

[mr_nitroz]

I would check cables, there isn’t anything else. Maybe try for test to run new wires and pins...

[Rawediag]

Thanks, problem was in engine wiring. Caused by leaking water temperature sensor. Video in link.