W221 Om642 DPF Differential pressure sensor

[mbmb123]

Here we go again, I get the battery replaced which fixes the stop/start function, and now it throws a DPF error. I'm not impressed with Mercedes reliability.

About a month ago it went into limp mode and threw an error saying it has received an unfeasible value from the differential pressure sensor. I bought a new sensor from the dealer in anticipation. Today limp mode again and the same pressure sensor error along with "your DPF is defective".

I'm hoping it's all down to the pressure sensor, and not the DPF, so I attempted to change it.
On the 2012 S350 two metal pipes leave the DPF and head north. They turn into rubber pipes which terminate on the firewall in the engine bay.

You have to remove a shiny metal heat shield to gain access. And then unscrew a metal bolt AND plastic nut to free the sensor from the its bracket. I got that far today before the light faded was faced with the "on time" hose clamps.

I assume they are "one time" use and I'll have to cut them off. Any advice on removing the clamps without damaging the rubber hose? And should I also replace the rubber hose? They look OK.

 

[BTB 500]

Hope that fixes your issue. If it helps any we've had a range of sensors fail on the OM642 in our Vito over the last couple of years (including DPF pressure and temp. ones), but the DPF itself has been fine (touch wood!).

 

[mbmb123]

Replacing the sensor now. I thought I was finished. I was just replacing the silver heat shield and I noticed the rubber pipes sticking out.
They should be flush to the firewall and behind the heat shield. The pipes are definitely attached correctly, they're different sizes. Maybe I've twisted the pipes causing them
to bulge? Oh well, when the rain stops hammering down I'll take a closer look. At least now the one-time hose clamps are replaced with jubilee clicks
it'll be easier pulling the pipes off if needed.

 

[mbmb123]

Done. Just a quarter turn in the rubber pipes made them behave themselves.

 

[mbmb123]

Viz Top tips:

When removing the silver heat shield, unscrew 3 of the four retaining fasteners. The forth, which look like a pancake, doesn't have to be unscrewed as at that point the silver heat shield has a slot not a hole.
So you can pull the heat shield free.

You can remove the on-time clamps by gripping them with some cutters, not to cut them, but to twist the ear and break it free.

Once the clamps are gone, unless you have fingers like the hulk, you'll have to grip the pipe gently with some needle nose grips and twist them off.

When attaching the new sensor make sure the pipes are flush against the firewall.

 

[Trickythemerc]

The hose clips are clic-r type and require a specific tool to remove and refit them. They are available from US Pro via Amazon for the price of a couple of pints.

 

[megaguru]

good job well done

 

[mbmb123]

It went into limp mode again, nothing indicated on the dashboard, but you get reduced power and strangely reduced gear selection.
Connected the iCarsoft reader and pulled this from the engine module:
"15FD00 the lower limit value of component B28/8 ( Differential pressure sensor (DPF) ) was dropped below / not reached". The same code as previous two occasions.
Turning the car off and on restored it to normal operation.

So what now?

 

[HITECH]

firstly. where was the dfp sensor supplied from? Was it genuine or was it aftermarket ? If u sourced a cheapo one then I can gaurantee u it will be useless. when u replace the dpfe sensor. u have to clear all codes. then replace it then clear all codes again. it sounds more like a MAF problem to me which is a very common problem that sends mechanics up the garden path when this dpf sensor fault kicks the car into limp mode.

 

[BTB 500]

My local (trusted) garage spent 2 weeks trying to diagnose and fix one limp mode episode on the OM642 in our Vito. There were fault codes that their system couldn't clear, even after parts had been replaced (fuel pressure sensor and EGR valve). In the end I took it to a dealer - it was sorted on STAR same day.

 

[mbmb123]

The part came from the dealer. The code was cleared with icarsoft. The car ran ok for a few weeks until it threw the same code again.

 

[mbmb123]

Car when to local specialist last month for various issues, one of which was to examine the DPF system.
Apparently its OK, but he "properly reset" the system as I'd changed the DPF pressure sensor.
Well, I do a regular 25 mile trip, and can say the mpg improved from about 36 to 40! I know it was getting warmer, but I still think there was a significant improvement.

I speculate that the computer tries to run the car as efficiently as possible given the various readings from sensors, but if it looses confidence in the sensors it
reverts to a safer, richer fueling map rather than try to lean it out. Or maybe that's b*llocks, because it STILL throws the same errors while maintaining better performance :-(

 

[Dingaling]

Watching with interest as I just got very similar. I am suspecting sensor needs replacing (same age too). Interesting that you seem to need a real STAR system to tell the ECU though.
Also surprised to hear that DPF regen won't happen at motorway speed (>100kmph).

 

[Dingaling]

Well my local garage took it and found loads of errors (my OBD could only see 2). It didn't make sense. Turned out to be 'rodent damage'.
Yes, I had parked under a tree full of noisy squirrels and the little buggers had chewed through the wiring loom from the CAT/DPF area to the engine bay/ECU. Its a wonder it ran at all.
A few restored connections later and the car is running sweet again. Cost about the same as a sensor replacement!
Now where is my shotgun.... (just kidding, but I might need to find some repellent to stop it happening again).

Moral - when getting sensor errors, or sensors 'not working'. Check the connections first. They can break (or be chewed) and the sensor itself is fine.