Failed MOT today

timmus

A2OC Donor
I'm also in the 'minimal knowledge' category when it comes to petrol A2s but came across this general VCDS diagnostic guide which covers O2 sensors and Cats - www.vwaudiforum.co.uk/forum/archive/index.php/t-140004.html
Can't vouch for its accuracy but the test procedures look promising

Cheers Spike
That's a really helpful page, Spike. Thank you. Hopefully a lot of this, such as measuring block values, will also apply to the A2 FSI ECU.

I would say understanding the low lambda value should be the first port of call for diagnostics.
Thank you, Andrew. Have you a recommendation on how this might be best achieved?

Cheers,

Tom
 

steve_c

A2OC Donor
I'd consider the A2's petrol engines to be the great hole in my knowledge, simply because I don't own one.
My own petrol A2 is the straightforward 1.4, and my knowledge around the 1.6 is pretty minimal, to be honest. However, I am aware that the FSI has not only two lambda sensors in the exhaust system, but also a NOx sensor. A raised NOx level triggers a brief injection of petrol into the exhaust, which ignites when it reaches the hot cat, thus reducing the NOx emissions to an acceptable level. When the FSI is working entirely as intended, and with an original exhaust and cats in good condition, this works very well, but of course key original exhaust components are no longer available. The cats, when they were available, were not only exceptionally expensive, but were only available on an exchange basis. Once the system is less than perfect (and rust is ever present of course) the cats are sadly prone to early failure.

The FSI exhaust is shown here:

Tom, this doesn't really help you much, if at all. But others may well read this thread who have acquired FSIs with little or no understanding of the complex technology involved, and I hope that it will assist them at least.
 

timmus

A2OC Donor
OK folks, here are the ECU scan results...

RZX FSI ECU.JPG


It seems that the NOx sensor is the culprit. I'm guessing that the failure of this sensor could be the cause of the emissions test failure..?

I had a good look through the various measuring blocks, but VCDS doesn't contain a label file for the FSI's ECU, so the measuring block definitions are vague at best.

Cheers,

Tom
 

steve_c

A2OC Donor
A useful thread on changing the NOx sensor:
 

vagdream

Member
OK folks, here are the ECU scan results...

View attachment 62422

It seems that the NOx sensor is the culprit. I'm guessing that the failure of this sensor could be the cause of the emissions test failure..?

I had a good look through the various measuring blocks, but VCDS doesn't contain a label file for the FSI's ECU, so the measuring block definitions are vague at best.

Cheers,

Tom
I've had lots of error codes on our FSi, but I have never seen anything that has been emissions/NOx related!
 

spike

Well-Known Member
Best guess time....... Nox (oxides of nitrogen) is a product of high combustion temps combined with the fact that almost 80% of the air going into the cylinders is Nitrogen. Normally the Lambda sensors control the air fuel ratio but it's possible the Nox sensor can override this if it measures high levels of Nox at the tailpipe.
A rich air fuel mixture reduces combustion temps and thus Nox levels - but must surely increase CO levels at the same time.
As the diagnostic scan highlighted Nox sensor faults, it's possible the inaccurate readings are leading to a permanently rich mixture which could be the cause of the high CO levels on the MOT test

I've chosen these words carefully as I may have to eat them at a later date

Cheers Spike
 

spike

Well-Known Member
A bit more research and possibly another piece in the jigsaw -
The MOT test results also show low Lambda readings. This equates to a low fuel to air ratio IE. a rich mixture and high CO levels

The NOX sensor is quite expensive but needs changing anyway so I'd be tempted to do that first and see how it affects the Co and Lambda readings
With a bit of luck, WOM may have first hand experience of this and confirm (or otherwise) the theory

Cheers Spike
 

RZX

Member
A bit more research and possibly another piece in the jigsaw -
The MOT test results also show low Lambda readings. This equates to a low fuel to air ratio IE. a rich mixture and high CO levels

The NOX sensor is quite expensive but needs changing anyway so I'd be tempted to do that first and see how it affects the Co and Lambda readings
With a bit of luck, WOM may have first hand experience of this and confirm (or otherwise) the theory

Cheers Spike
Thanks for that Spike, the car is going for a retest on Wednesday to see if the Cataclean has bought the readings down (it's free and the only chance we will have) then it's over to WOM. I really hope it can be sorted because I love the car and it drives lovely without any clonks or bangs etc.
Will update later
 

audifan

A2OC Donor
May also be worth a fuel system cleaner on top or even a second Cataclean and GOOD fuel. Try to get some miles on the car as these cleaners are not instantaneous due to the dilution and cleaning process. Have also had good results from Ecomotive Clean Drive Advanced Fuel And Exhaust System Cleaner.
 

RZX

Member
May also be worth a fuel system cleaner on top or even a second Cataclean and GOOD fuel. Try to get some miles on the car as these cleaners are not instantaneous due to the dilution and cleaning process. Have also had good results from Ecomotive Clean Drive Advanced Fuel And Exhaust System Cleaner.
Thanks for that
 

chumsofmanutd

A2OC Donor
Hi guys,

Sorry for the late response in here. We agree with @spike's analysis. @RZX , best of luck with the Cataclean but unfortunately we think it is unlikely to help, or at least not a permanent fix. We would recommend the NOX sensor issue needs resolving first and then the exhaust emissions should be reanalysed. Also, resolving the 'inlet manifold tuning valve' DTC is likely to increase performance. Changing the catalyst would be a very last resort.

Let us know how you get on.

Cheers

Rob.
 

RZX

Member
Hi guys,

Sorry for the late response in here. We agree with @spike's analysis. @RZX , best of luck with the Cataclean but unfortunately we think it is unlikely to help, or at least not a permanent fix. We would recommend the NOX sensor issue needs resolving first and then the exhaust emissions should be reanalysed. Also, resolving the 'inlet manifold tuning valve' DTC is likely to increase performance. Changing the catalyst would be a very last resort.

Let us know how you get on.

Cheers

Rob.
Thanks for that Rob, will probably look at bringing it down to you later this week or early next and leave it with you, assuming you are still operating in these strange times.
Thanks for your input, I will be in touch soon
 

chumsofmanutd

A2OC Donor
Thanks for that Rob, will probably look at bringing it down to you later this week or early next and leave it with you, assuming you are still operating in these strange times.
Thanks for your input, I will be in touch soon
No problem, sure. Just give us a call and check before hand . We’re still currently open but with a significant change in protocols to keep everyone as safe as possible, things could be very different by the end of the week though.

Cheers

Rob


Sent from my iPhone using Tapatalk
 

A2Steve

A2OC Donor
There’s always the Pro Boost map to eradicate the Nox/lambda completely.

The only issue is, with Germany also on lockdown now I have no idea when I’ll be receiving batch 3. Haven’t heard from Pro Boost for a week.
 

PlasticMac

Member
Not so. That link says:
Vehicle approval tests are not the same as MOT tests, which check your vehicle meets road safety and environmental standards each year. The Department for Transport is keeping MOT testing for cars, motorcycles and light vans under review. Check back for updates.

So, MoT still required. For now, at least...

Mac.
 
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