Mercedes CLA 220 CDI DPF pressure sensor

[PARESH]

Hello

I wonder if anyone knows how the change the DPF pressure sensor on a 2014 Mercedes CLA 220 CDI. The car is initiating a DPF regen but the soot levels are not decreasing during the regen. I have monitored the regen parameters with an iCarSoft V3 and the temperatures are rising to around 650 degrees during a regen (when the soot level reaches above around 105%). I have taken the car on a 300 mile motorway drive and watched the DPF fill levels and DPF temperatures etc during the journey and see the fill level gradually rise and then the DPF temperature rise when a regen is happening but the fill level is decreasing very slowly and after about 20 minutes the regen is aborted with the fill levels still quite high. I suspect that the DPF pressure sensor may be defective. There are no fault codes stored in the engine ECU.

I have tried to change the DPF pressure sensor located on the firewall behind the engine but access is extremely restricted! I don't want to start removing other parts in order to gain access if I don't have to. It appears that removing something that looks like the EGR cooler pipes will improve access but I am reluctant to do this in case I create an air lock in the coolant system.

Also, I just found out that there are TWO pressure sensors for the DPF on this vehicle (651.930 engine with EURO 6 exhaust gas cleaning). Where is the second sensor located and what is its function? From diagrams I obtained from an online EPC, I think that this second low pressure sensor may be located underneath the vehicle.

I would be extremely grateful if someone with access to WIS could send me the documents on how to change the two DPF pressure sensors.

 

[M80]

Mine is Euro 5, so no adblue.
The DP sensor is on the fire wall, with the 2 rubber hoses from the DPF feeding it.
I could imagine the exhaust back pressure sensor being involved in the fill calc, that's way back, n/s, topside of the EGR casting.

How often does it attempt to regen? As they fill with ash that frequency increases as it can't be incinerated by a regen but does block the EGR. So the 100% trigger point is reached more easily., and of course it will always seem fairly full.

 

[PARESH]

My car doesn't have Adblue either but it is a Euro 6.

I have located the DP sensor on the firewall but there seems to be another differential pressure sensor (looking exactly like the DPF sensor but with a different part number) located away from the DPF differential sensor on the firewall. See the diagram below.

Items number 150 are the two identical looking pressure differential sensors.

OM 651+927 refers to the Euro 6 exhaust cleaning

The car attempts to regens as soon as the fill level reaches around 105%. but the fill level never drops below approx 90% and then it slowly climbs to 105% and the cycle restarts. This levels can be reached quite quickly if tottering around city roads but will take longer on a motorway journey. When the DPF is regening, the DPF will not fill up so quickly. When the regen stops the rate of fill changes to a more normal rate. Also, an iCarSoft reading showing the number of previous regens increases by one. I presume that this is the number of failed regens. My car is showing the number of previous regens as 20 and hence I take this to be the number of failed regens as the car is a 2014 model with 95K miles

I'm thinking that either one or both of these differential sensors is faulty and giving incorrect readings to the ECU

- .

 

[Droverunner]

Could I ask where you find these great exploded diagrams?

 

[M80]

Mercedes > Mercedes EPC Online > nemigaparts.com

Parts catalogs. Spare parts catalog Mercedes EPC Online. Mercedes.

nemigaparts.com

Useful, but the ads can be a nuisance.

 

[Droverunner]

Ahh yes a bit ad heavy but a great resource thanks. Prices of the items I checked about right too.

 

[M80]

Paresh,
I'm going off the 651 diagram. Is it possible that the diagram is showing not 2 DP sensors but an A or B set up on different models? That would leave you looking for the 2ndthat isn't there.
Fairly easy to confirm I would have thought by following any rubber pipes back to sensor/s.

I can't think of anything other than the DPF that has a differential to monitor.

My earlier comment about ash blocking the EGR should have read DPF.
As long as parameters haven't been reset Star will show the ash level, although I believe that to be an assumption from calculation.

 

[PARESH]

Paresh,
I'm going off the 651 diagram. Is it possible that the diagram is showing not 2 DP sensors but an A or B set up on different models? That would leave you looking for the 2ndthat isn't there.
Fairly easy to confirm I would have thought by following any rubber pipes back to sensor/s.

I can't think of anything other than the DPF that has a differential to monitor.

My earlier comment about ash blocking the EGR should have read DPF.
As long as parameters haven't been reset Star will show the ash level, although I believe that to be an assumption from calculation.

Hi Martin

This is what I initially thought but have confirmed with Mercedes that there are TWO DPF pressure differential sensors.

I will have to raise the car on a lift to have look underneath to find the sensor. As you say, following the pipes will lead to the sensor. I was hoping that the sensor would be in the engine bay and hence easier to change.

The one in the engine bay on the firewall looks a pain to change as there is very little access without removing the water hoses to the (I think) EGR cooler.

Does anyone have access to the WIS document to change to sensor in the engine bay please?

 

[M80]

Always good to learn,
unfortunately this lesson is at your cost. 2 DP's ffs.

My DP is screwed onto the reverse side of a plate, held to the engine by 3 torx screws, not such a great issue.
Mine is single turbo so more room in there though.

 

[PARESH]

So, I think the Euro 6 has two DP sensors!! The one in the engine bay is screwed onto a plate attached to the firewall. There is very little room for movement even if the plate is detached from the firewall. They could have placed the sensor in a more accessible location!!!!