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Low air flow problem
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vaho   
Wed Oct 12 2016, 05:59am
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 Hi all. To get to the point, my car has a constant fault code appearing "low air flow - rear". It dosen´t cause the MIL light to lit up but when I drive with constant low speed with revs 1500-1600 I get the MIL light and the same fault code. Looking to the data at idle the rear flowmeter is showing some 120-160 mg/stroke while the front one showing over 300. At higher revs (over 3000) the number is getting more equal but only when the revs are over 3000. When I release the accelerator after revving the engine the rear one drops to 20-50 mg/stroke for a moment. It also drops as much when EGR valve percentage drops so in case they are closing. All the EGR percentages are equal, when they are lets say 40% or 5%, they are allways all the same only with some minor intermittant fluctuations. No limp mode or performance problems.

Flowmeters are good, changed them with one another and low airflow remained to the rear. I changed the rear turbo for different reasons (vanes sticking) and was thinking that maybe this helps with low air flow too, but it didn´t. I checked the engine breather valve, since the outlet is connected to the rear air duct, but closing the valve didn´t made any signifficant difference in air flow. There are no apparent cracs in the air ducts.

So I was thinking and maybe some of you had the same experience that in this case it maybe the rear EGR valve not moving correctly after all. Can it affect the air flow if it is not moving correctly although there is now EGR related fault and the position percentages are broadly all corresponding?

Thank you!
Hattershaun   
Wed Oct 12 2016, 08:03am
Joined: Dec 19 2010
Member No: #320
Location: Bedfordshire, UK
 My first C6, a 2.7HDi, showed the 'airflow fault', as I was experiencing a slight hesitation in acceleration at 1500-2000rpm
I changed both airflow meters first, which made no difference.
This progressively got worse and eventually the engine management warning light came on.
One of EGR valves was replaced, which cured the fault.
vaho   
Wed Oct 12 2016, 08:53am
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 Thank you for the answer. I do not experience any hesitation though. And the engine light dosen´t come on unless I deliberately drive slow and steady with revs 1500-1600. I just hooked Lexia up and there was another message "inconsistency between flowmeters" or something like that. No warning light and performance issues. I too tend to think that the EGR is the likely suspect. That rises another question, while OE ones are costing over 200 euros (Valeo) there are some for sale on ebay.co.uk for less than a 100. Does anybody has any experience with the cheaper ones?

Made some pictures (starting from idle then revving up to 2500, 3800 and idle again), maybe somebody can read something out. One thing that bothers me a little is the flowmeter air temperature reading over 30 degrees when the temperature outside was some 7-8. Is it correct because flowmeters are located at the beginning of the air intake and should show the temperature near the outside temperature I think?
321dave   
Wed Oct 12 2016, 10:35am
Joined: Sep 09 2011
Member No: #614
Location: Dublin
 Hi Vaho,
is that the 0299 fault code-low air flow. I had that code appear intermittently recently and i found a small crack in the pipe leading from the intercooler up to the throttle body had a small crack and was leaking a little boost. but again no mil light but a little hesitation around 1500-1700.
vaho   
Wed Oct 12 2016, 11:47am
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 No it wasn´t. I dont´t remember right now what the number actually was but in wording it was something like "Air flowmeter rear-air flow too low"

The code P0299 is turbo pressure signal fault, turbo pressure too low which is of course expected if there is crack somewhere in the pressure side of the pipe.
vaho   
Wed Oct 12 2016, 12:02pm
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 Ok, I looked it up end the numbers were P0104 - Air flowmeter (rear) signal fault: Flow too low and P010F - Air flowmeter signals fault: Coherence of flow between the 2 air flow sensors.
vaho   
Wed Oct 12 2016, 04:34pm
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 So, managed to block the airflow from the rear EGR as suggested in other related post and indeed, the airflow from the rear flowmeter increased significantly. Got no warning messages from the blocked EGR.
Rear EGR it is then, oh joy! Got to do it before the freezing winter temperatures.
321dave   
Wed Oct 12 2016, 07:21pm
Joined: Sep 09 2011
Member No: #614
Location: Dublin
vaho wrote ...

So, managed to block the airflow from the rear EGR as suggested in other related post and indeed, the airflow from the rear flowmeter increased significantly. Got no warning messages from the blocked EGR.
Rear EGR it is then, oh joy! Got to do it before the freezing winter temperatures.



So you've found that the EGR valve is faulty Vaho, as in it was open when it should of been closed? I think G has replaced the rear EGR valve. You probably read those posts already.
vaho   
Wed Oct 12 2016, 08:12pm
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 I didn't get to that point to confirm that because I blocked it from the inlet side of the tube to the air collar with a piece of cardboard which was available near the car. When I then ran a parameter test the EGR valves were actually open but airflow was turned around and the front was showing signifficantly lower numbers. Couldn't run the engine long with the piece of paper attached to it though. Revving the engine closed the valves and airflow equalized. After that I connected the pipe and got the usual rear flow much lower than the front.
Yes, read all the relevant posts. Interesting is that somebody sometime has done something with the rear valve beacuse the coolant hose clips are jubilee not the originals. Maybe even changed the valve. I wonder if driving with rear turbocharger with actuator rod detached as it was the case with the car can affect the EGR. Who knows when the rod was disconnected.
gmerry   
Wed Oct 12 2016, 09:25pm
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Its possibly better to just blank off both EGR valves rather than replacing them.

regards
G
eke   
Thu Oct 13 2016, 02:58pm
Joined: Sep 16 2011
Member No: #624
Location: Oulu
vaho wrote ...

That rises another question, while OE ones are costing over 200 euros (Valeo) there are some for sale on ebay.co.uk for less than a 100. Does anybody has any experience with the cheaper ones?


I have ordered one cheaper OE from Estonia, from here: - Click Here -
gmerry   
Thu Oct 13 2016, 03:41pm
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Hi, for my 2nd EGR valve replacement I used an alternative from a UK motor factor and the price was less than half. When I pulled out the OEM EGR valve it turned out Citroen had been sourcing non Valeo too.

regards
G
vaho   
Thu Oct 13 2016, 05:15pm
Joined: Jun 25 2015
Member No: #2228
Location: Tallinn
 Thank you all! I will update if I get to the point where there are some results.
e3steve   
Fri Oct 14 2016, 05:53am
Joined: Jan 21 2013
Member No: #1163
Location: Warsash, Hants & Palma de Mallorca, Spain
gmerry wrote ...

Hi, for my 2nd EGR valve replacement I used an alternative from a UK motor factor and the price was less than half. When I pulled out the OEM EGR valve it turned out Citroen had been sourcing non Valeo too.

regards
G
Or possibly Ford, Gordon; the Lion engines were built in Dagenham...
eduardomaio   
Sat Oct 15 2016, 10:23am
Joined: Apr 18 2012
Member No: #869
Location: Lisbon
 I had the same issue vaho, my experience was the same, i had switched and cleaned the airflow meters and the issue was still at the rear.

But in my case I had an error related with the EGR appear and a slight hesitation between 1500 / 2000rpm. After replacing the rear EGR there were no more errors regarding the airflow.
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