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PO401 fault code

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darrenjane

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Hello - after advice on my 61 plate 180
Further to my previous post re PO403 fault code this has now been cleared (by VW dealer over a remote connection from Germany I’m told). However we are now getting EML and PO401 “exhaust gas recirculation “A” flow insufficient detected”. I returned to dealer who advised that as the EGR valve had been replaced it just needed a good run to clear the system and there should be no issues with driving unless red light/ flashing light/ limp mode. I initially had the AA clear the fault. However I’ve now got a carista obd device where I can check and clear faults when the appear. We are currently in the French alps with the vehicle but the EML keeps appearing intermittently. Not on every drive and sometimes self clears and the light goes out. I’m running on bp ultimate diesel as told this may help to clear the system. Appears to drive fine even with amber EML on.
Any thoughts/ ideas appreciated- many thanks
 
Changing the EGR valve is good, but why was it changed and at what mileage?

The Diesel Particulate Filter in the exhaust may be clogged up due to the old valve being stuck open. Normally the computer would handle this without your knowledge and all should be well, but it may not have cleaned the DPF sufficiently so you may need to force the engine to regenerate the DPF. 20-30 mins motorway driving is what is recommended.

This link may help
https://www.rac.co.uk/drive/advice/emissions/diesel-particulate-filters/

Alan
 
As @AlanC says, the light may be for a different issue like dof getting clogged, but P0401 only relates to the EGR so:
did they change it? Or just clean it?
Did they change it but actually its the sensor giving incorrect flow readings?

If you have just had the work done, take it back.
 
Thanks both for your replies
The egr was replaced as was completely seized/ clogged with black oily soot. It was seized partly open, so assume as you both mentioned this may have gone through to the dpf. Sounds like I need to try and get it to regenerate- do you know how long/ far I would have to drive to get it to go this? I have read 20-30 mins at greater than 2500 rpm and 40 mph - is this correct and how would I know if it is/ has regenerated? How long would the regeneration take?

Do you know if there is a particular sensor which measures the flow and could be triggering the fault?
Many thanks
Darren
 
That fault code only links to egr and will not be caused by any other component. Did they change the valve or the whole cooler assembly ? As it’s the cooler that internally cloggs, also was the pipe work changed from the head to the egr cooler and the egr cooler to the inlet manifold these also clogg up and cause an issue
 
Hi, thanks for the reply. The egr valve was replaced but the cooler and pipe work were inspected and appeared to be clear ( as far as you can see - it is obviously difficult to fully check the cooler internals).

As I mentioned we are currently away in the French alps. It’s strange that I can sometimesdrive for 200 miles on motorway will no warning light, yet a quick trip to the shops can make it appear, but this isn’t always the case and there doesn’t appear to be a common pattern??

Engine has had a good run to here circa 1800 miles with lots of mountain passes all on bp ultimate diesel so hoping this would have helped to clear things??
 
Hi, thanks for the reply. The egr valve was replaced but the cooler and pipe work were inspected and appeared to be clear ( as far as you can see - it is obviously difficult to fully check the cooler internals).

As I mentioned we are currently away in the French alps. It’s strange that I can sometimesdrive for 200 miles on motorway will no warning light, yet a quick trip to the shops can make it appear, but this isn’t always the case and there doesn’t appear to be a common pattern??

Engine has had a good run to here circa 1800 miles with lots of mountain passes all on bp ultimate diesel so hoping this would have helped to clear things??

Hi if you get a chance could you take a picture of the part number on top of the egr cooler that would be useful as this is normally the fault I suspect if the vealve was as clogged as you say then the inside of the cooler will be totally choked up with carbon. The fault will be intermittent at the moment because the valve is new and there will be some flow through the cooler depending on engine loads etc.
 
Thanks both for your replies
The egr was replaced as was completely seized/ clogged with black oily soot. It was seized partly open, so assume as you both mentioned this may have gone through to the dpf. Sounds like I need to try and get it to regenerate- do you know how long/ far I would have to drive to get it to go this? I have read 20-30 mins at greater than 2500 rpm and 40 mph - is this correct and how would I know if it is/ has regenerated? How long would the regeneration take?

Do you know if there is a particular sensor which measures the flow and could be triggering the fault?
Many thanks
Darren
There should be a sticker in your cab top right of screen. I believe it is 2000-2500 rpm (not over it wont work), about 20 mins I believe. The regen can be triggered via the obd port manually by an engineer I believe.

http://www.vwgenuineparts.co.uk/DPF_regeneration.shtml
 
Have attached photo of sticker on cooler, partly damaged but hopefully of some help.

BFF7E40E-4320-4A90-AEF6-73EC25D08807.jpeg
 
Have attached photo of sticker on cooler, partly damaged but hopefully of some help.

View attachment 36674
Thanks that is the original egr cooler unit. There have been several revisions of this part over the years the latest has a plastic type coating over the internal aluminum fins to stop the carbon build up you will require a complete egr cooler assembly as I suspect there is not much left inside that cooler of the original aluminum fins and it will be full of carbon. Unfortunately in this instance the diagnosis of just the valve was incorrect.
 
Ok many thanks for the advice on this one - looks like it’s a new cooler for me...
 
Hi just thinking about this. Does anybody know which sensor detects this low flow and therefore flags up the fault code? To be thorough i would also like to check this sensor.
Thanks
Darren
 
Hi just thinking about this. Does anybody know which sensor detects this low flow and therefore flags up the fault code? To be thorough i would also like to check this sensor.
Thanks
Darren
Looking at the manual, there is no flow sensor as such, the system uses 3 temperature probes to access the temperature and measure the cooling effect of the gas leaving the cooler.
upload_2018-8-22_8-54-2.png
It also has a differential pressure sensor so this could be used measure the pressure difference across the cooler , but its not clear in the diagrams where it is measuring from/connects to..
upload_2018-8-22_9-18-8.png

Maybe @Vw guru can clarify for me??
 
Looking at the manual, there is no flow sensor as such, the system uses 3 temperature probes to access the temperature and measure the cooling effect of the gas leaving the cooler.
View attachment 36846
It also has a differential pressure sensor so this could be used measure the pressure difference across the cooler , but its not clear in the diagrams where it is measuring from/connects to..
View attachment 36847

Maybe @Vw guru can clarify for me??

Hi it’s actually worked out by a calculation in the engine Ecu ( exhaust gas map) by comparing the incoming air flow from the air mass meter against the duty cycle of the egr valve. G505 as shown in the picture is the differential pressure sensor for the dpf to calculate soot mass and work out when a regen is due also the temp sensors are for measuring the temperature across the dpf. The part to check would be the air mass,but I suspect that is fine and the egr cooler is clogged. This would be causing the air mass meter readings to be incorrect against exhaust gas flow from the ecu map flagging the low flow fault code as intake air readings are not dropping when the egr valve opens.
 
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Many thanks for the detailed explanation, very useful.
 
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