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Took these readings under mild acceleration, see the screenshot. Specifically, "negative" ash contents and the DPF pressure difference of over 11 bar (?)
I would not trust these readings much, putting the scanner as a first suspect, and the diff pressure sensor next. However, the ECU seems to interpret the readings as a seriously clogged DPF (which is not, as the car run perfectly the day before) and limit the boost pressure to "save" the engine. As a result, no acceleration...The lines from DPF to the sensor seem to be OK as I disconnected them and tested with compressed air -- no apparent resistance.
So my options are:
1. Throw away or upgrade iCarSoft, as it shows garbage values.
2. Replace the original sensor, as it threw the 11DA00 code a couple times
3. Something else to consider, short of swapping out the DPF?
I experienced iCarsoft giving me bogus data before, so definitely start with getting 2nd opinion.
Autel sells dongles for $50, what makes much nicer scanner and having model-specific software makes for better troubleshooting.
For additional $20 you can add software for different car.
The 11125 mbar (150+ psi) is not feasible. I'd bet that sensor is bad. It's a cheap part and a 20 min swap (non OEM $24 on fleabay). That's where I would start.
For the back pressure reading, I believe you have to subtract atmospheric pressure to get back pressure relative to atmosphere. But it's still high.
For that, I would check back pressure manually using an old school back pressure gauge screwed into the upstream oxygen sensor fitting. Check it at idle and 3000 rpm. If it's low at idle and <4 psi at 3000 rpm, it rules out a lot of bad things.
If it's high, I'd work the gauge downstream to isolate the blockage.
If DPF is, in fact, full of whatever, I'd clean by pre-soaking overnight with hot de-greaser (home depot) and then soaking 2 hours in 1 to 5 solution of muriatic acid (home depot) to water. I had to figure this out because MB does not sell the DPF for my pre-def om642 any more.
To me, ash content reading is worthless if actual pressures are good. It can be zeroed with DAS and some scanners once other sensors and readings are confirmed to be in acceptable range.
I'm just telling you what worked for me. Corrections by pros with more experience/knowledge are appreciated.
Swapped out the diff pressure sensor with an aftermarket one and calibrated it using an Autel AP200M BT dongle (my old iCarsoft still shows > 3000 mbar with the engine off). The new sensor range is between 5 hPa (idle) and 50 hPa (moderate acceleration), which is definitely more realistic. As a side effect, Autel shows the exhaust back pressure number turning red when it exceeds some 2000 mbar -- could be yet another sensor to check/replace. Thanks for your advice on the tool.
Does cleaning a DPF as a regular thing like every year help them last the life of the oe642? Or will bypassing my PCV be enough?
DPF is cleaned/regenerated by computer at regural intervals, or when it is needed sooner.
If you are that curios - pull history of regeneration from ECU.
06-26-2021, 07:19 PM
