VRS TDi with 650mg measured soot value! runs fine.

[Rob043]

Hello, hoping for some advice on my high measured soot value. 

 

I have a 2013 tdi VRS with 79,000 miles on it. it gets a mix of town and longer drives, regens usually twice per tank of fuel which is about 450-500 miles and seems to work well in terms of power and economy with no error lights. 

 

Out of curiosity, realising the 'Carly' OBD dongle i have would give me live data on the DPF i tried it out and saw a calculated soot value of around 10mg and a measured value of about 650mg. I checked again at the next regen, and the calculated changed from 20 something i think, down to about 5mg by the end of the regen. The measured had a similar drop rate and ended up at about 640mg. 

 

Why is that measured soot value so implausibly high? I think the regen frequency i have is ok, and the car has no issues, but i'd like to have an answer! Is this an issue with the exhaust pressure sensors?

 

Thanks in anticipation.

 

 

[varooom]

Welcome to the forum,

 

Take the measurement of the Soot with engine off, if the value is high like it is now, then sensor will most likely be goosed.

[Rob043]

Thank you. Checked today and it’s still the same high value with the engine off. So I may try a sensor. I think I see it once I unwrapped the heat shield, it has two hose barbs with only one hose attached. I presume that’s the way it’s mean to be as there are no other hoses. 
 

has anyone got a brand recommendation for a replacement sensor ? I see lots of options on AutoDOC 

[varooom]

57 minutes ago, Rob043 said:

Thank you. Checked today and it’s still the same high value with the engine off. So I may try a sensor. I think I see it once I unwrapped the heat shield, it has two hose barbs with only one hose attached. I presume that’s the way it’s mean to be as there are no other hoses. 
 

has anyone got a brand recommendation for a replacement sensor ? I see lots of options on AutoDOC 

 

That part number was dropped, now please find 03L 906 051D

Unless you have a wiring fault, that amount it reads is off the charts, so this would likely be what I would change.

 

Older generation sensor's used a pipe on both ports of the sensor, either side of the DPF

New gen sensor's only measure pressure one side and it vents the other to atmosphere, so perfectly normal

 

I am sure the new gen's don't need adopting, mine does not have to be done.

 

When you get new sensor, measure soot with engine off then with engine on.

You then should probably do a DPF regen, checking the soot afterwards to verify that all the functions are correct with the car.

Edited 24 December, 2022 by varooom
Additional Information

[Rob043]

Thanks very much for the help. I’ll try a new one to the newer number 

[Rob043]

Thanks again. I’ve fitted a new sensor and now have a sensible value for measured soot. About 20mg difference from the calculated now but that seems typical enough. I’ll keep a check on it and see if the regen frequency changes at all. 
 

sensor replacement came from Darkside developments website as they had a genuine sensor advertised at about £35 posted. 

[varooom]

Ideally you want to do a static regen process, to see if you can get the soot down (measured) to definitely sub 5g.

 

In a healthy system it should drop to 1-3g at the end of regen process.

 

There's a chance the soot has kind of "baked" on, so try to get the values for your car.  You run the risk of permanent DPF regeneration maybe, and all the fuel that would waste

[Rob043]

There is a fly in the ointment. 

 

I was monitoring values on a  recent journey and the measured soot value is back up as it was around 650mg. Not ideal. 

 

I emailed the supplier and they suggested checking wiring and checking for an exhaust leak as that could damage the sensor if its nearby. Ive had a look at don't see evidence of a leak. I'm still corresponding with them so will see if they have any other suggestions, or want to replace the sensor. 

 

 

[Rob043]

[varooom]

How odd, usually a wiring fault would show up as short to Earth/open circuit.

The ECU on the other hand, might be going wrong internally somehow.

 

Do you have a full VCDS scan of the car currently?

[Rob043]

I don't have VCDS i'm afraid, just the Carly app. I'll look in to getting set up with that if it would be useful. I am hoping to get another look around the engine bay at the weekend and see if i can find any issues with the vac pipe or wiring. 

 

I did unplug the pressure sensor as a test when the engine was idling, the measured soot value didn't change ( i thought it might have changed to 'no value'), and the ECU then recorded that open circuit as a fault only when unplugged, no faults otherwise. 

 

Thanks for all the help Varooom!

[varooom]

Do you have a part number for the new sensor (picture is ideal) so date on part can be seen.

[Rob043]

Good idea. Please see picture. This is the same older B revision part that’s superseded? I did notice the newer revisions mentioned on the listing so expected a newer part but this seems to be dated August 2015. 
 

Perhaps I should try my local Skoda dealer for a revised part? 

[varooom]

Yes the part picture is week 34 of 2015 as you read, not sure if you want to pay main dealer prices for that part.  I did track down a part on eBay that is actually listed correctly https://www.ebay.co.uk/itm/275531758223

 

Of course it's your choice if you purchase from that link, buyer beware and all that.

 

 

I am more worried you will part with some cash and still not get this fixed, so was wondering if you have been out and wiggled parts of the loom/inspect that area whilst reading live values from your tool (if it will allow this?)

[Rob043]

thank you again, yes i have a had a poke about although that's fairly limited given the space, i didn't start dismantling. The wiring and vac hose were fine as far as i was able to see. As above I read out the measured soot value with the engine running also and had the sensor connector on and off and this wasn't affecting the reading. I did think it was odd that the read value didn't disappear but it was storing a fault code when i did unplug it. 

 

I think given that the value it gives is still sensitive to the soot load then the sensors sensitivity is there, but there is the big lump of added resistance making it a high reading. Given that i saw a good value initially before the car was started with the new sensor i think i will try the newer revised one. It could be that this old sensor gave up as soon as it was heated up the first time the car was used. its only a theory of course! 

[varooom]

Best of luck, hopefully you can put this to bed soon. 🤝

[DuncanDisorderly]

Just a thought, you say no difference in reading with the hose on or off, that's quite a narrow bore hose, could it be blocked? 

[varooom]

12 minutes ago, DuncanDisorderly said:

Just a thought, you say no difference in reading with the hose on or off, that's quite a narrow bore hose, could it be blocked? 

You're right about the pipe needing a potential blow out.  I am not sure @Rob043 has tested the sensor without pipe connected and engine off?

 

Out of curiousity I tested my sensor with the pipe off, and engine off and the sensor still read the same, about 5g 😆

[Rob043]

Thanks guys, Duncan you may have something on the dirty pipe. I went out to fit the newer sensor, it arrived from the ebay vendor with a late 2021 date and the 'D' on the part number. However, i first checked the reading on the sensor already on there and it was reding a good value of about 1g of soot. (I say gram, although carly shows milligrams unit, but i am taking this to mean grams). 

 

I left that one on, did a test drive, car was warm, of only a couple of miles and the value would vary. Increasing when on low load but decreasing when lots of throttle was used. So it seems ok for now.  

 

I'll check again for a good value before i send back the additional sensor. And continue to keep an eye on it. I'd like to see the distance between regens for a while. It has been around 400km i think, so would like to see if this improves at all. 

 

I say the idea of a blockage is good as i had used a can of JLM Diesel DPF ReGen Plus over a previous tank of fuel, and that may have cleared obstruction to the sensors location and sorted the issue. 

 

I will update with any developments. thanks again for the help. 

[varooom]

Glad to hear, hopefully this has put it to bed (for now)  I guess you are testing for a bit before sending back the "D" part sensor, let's hope that you are chugging along nicely now.