NOX (oxygen) Sensor!!

andrew767

New Member
Hi,

items 20 and 21 as per the above diagrams are the same thing, there are actually two different diagrams in the earlier post with different numbers.

The top diagram shows the placement of the sensor on the exhaust, number 20. The bottom diagram is how the same sensor, number 21 here, connects to the ECU. The NOx sensor is under the car and you can see it easily. It is to one side of the pipe and angled slightly upwards. I have changed this sensor in my first FSI. The wires goes through a hole in the floor in the passenger footwell and to the emissions control unit. This is a separate box to the engine ECU and is bolted to the floor. The wire goes from the exhaust and is clipped above the heat shield and the place where it enters is covered with a plastic cover that protects where the engine wiring also enters the car. This will need to be removed by undoing the retaining nuts and bolts. The gromet is part of the cable and this just pops out which allows the plug from inside the car to go through the hole to the ouside.

View attachment 47228
View attachment 47229
View attachment 47230

The NOx sensor is actually a combined sensor and acts as both a lambda probe and NOx sensor. It therefore costs more than a regular lambda probe. The lambda probe part forms the usual post CAT lambda check, and mostly is used to verify the correct operation of the calaytic converter. The second lambda sensor acts in the same way as in the FSI as it would do in a "regular" petrol car. If the lambda part is broken then the emissions control engine warning light will be on as the car can't verify that the emissions are correct. In my car, the lambda sensor part was OK but the NOx part wasn't working so the warning light was off but a fault code was logged for NOx. Unfortunatelly for me, after changing my sensor, the car then tried to run in lean burn mode and instead just told me that my inlet flap actuator was broken. :-(

regards

Andrew
Many thanks Andrew for your help and indeed I think the penny has dropped now!. Great pics along with explanation too. So I gather the first sensor is the same as the last one so guess that is why I have an odd reading of NaN% for the bank 1 2 sensor. The sensor in the first cat at the bottom is just a heat sensor I guess. Will try to order one guess if I order the same part code as the first one guess will fit the last one. Did you get your inlet flap sorted? rgds andrew
 

andrew767

New Member
Pleased that headway is being made with this issue. I don't know what's happened to the original 3 photos - they're not on my old photo bucket account, and as I don't have an FSi, I can't take any detailed photos of the sensor installation, so it's good that other FSi owners are stepping into the breach.
Hopefully, this can be resolved now at minimum cost - it's such a shame that these otherwise great petrol A2s can become scrap when in need of a couple of sensors, from a financial point of view.
Many thanks Skipton01 will update once I have replaced that sensor rgds Andrew
 

ajsellors

A2OC Donor
Many thanks Andrew for your help and indeed I think the penny has dropped now!. Great pics along with explanation too. So I gather the first sensor is the same as the last one so guess that is why I have an odd reading of NaN% for the bank 1 2 sensor. The sensor in the first cat at the bottom is just a heat sensor I guess. Will try to order one guess if I order the same part code as the first one guess will fit the last one. Did you get your inlet flap sorted? rgds andrew
Hmm, that first diagram from what you can see is confusing. Both pre first cat and post second cat sensors are labeled "20" in the top diagram but they are most definitely not the same part! The reference to label 20 is actually a link to the second illustration where the two different sensors are shown individually, except in the part of the diagram inserted in the post, the pre-cat sensor is omitted.

The pre-cat sensor (bank 1) is a regular lambda probe where as the post second cat sensor (bank 2) is a "special" combined lambda and NOx sensor. The second sensor seen in the top diagram just after the first cat is a temperature probe used for measuring the exhaust gas temperature. This is used as part of the lean burn control for the FSI.

I have labeled the first diagram below for clarification:

FSI exhaust.png
 
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andrew767

New Member
Many thanks ajsellors very helpful I realize now with your assistance the second cat sensor is different I was confused before. Strangely I have seen used sensors for this cat on ebay but no new ones as of yet not sure if they are worth the risk? rgds andrew
 

andrew767

New Member
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andrew767

New Member
Thanks, when I changed mine in 2013 I bought it from Audi for £139.74 + VAT (just looked it up).
Many thanks although for some reasons the part number 036906265H is not for the BAD engine code I have got the 2004 1.6 fsi rgds andrew
 

ajsellors

A2OC Donor
Many thanks although for some reasons the part number 036906265H is not for the BAD engine code I have got the 2004 1.6 fsi rgds andrew
Yep, that's the first pre-cat lambda sensor for the 1.4 petrol AUA/BBY on the A2.

First pre-cat for the 1.6 FSI is 047906262

Post cat 1.6 FSI lambda / NOx is 8Z0906216

regards

Andrew
 

andrew767

New Member
Yep, that's the first pre-cat lambda sensor for the 1.4 petrol AUA/BBY on the A2.

First pre-cat for the 1.6 FSI is 047906262

Post cat 1.6 FSI lambda / NOx is 8Z0906216

regards

Andrew
Many thanks Andrew that a great help will order one rgds Andrew
 

andrew767

New Member
Yep, that's the first pre-cat lambda sensor for the 1.4 petrol AUA/BBY on the A2.

First pre-cat for the 1.6 FSI is 047906262

Post cat 1.6 FSI lambda / NOx is 8Z0906216

regards

Andrew

Hi Andrew I have checked what has been fitted to the NOX sensor controller it 's only 4 wires seems to have been changed recently. Seems this is wrong it should have more wires to the sensor would you happen to know how many yours had seems it should be six?
 

ajsellors

A2OC Donor
Hi Andrew I have checked what has been fitted to the NOX sensor controller it 's only 4 wires seems to have been changed recently. Seems this is wrong it should have more wires to the sensor would you happen to know how many yours had seems it should be six?
I have just checked my NOx sensor in the car and there are 6 wires going from the sensor into the connector on the control unit.
Does it look like the wires from connector have been cut and spliced to different wires to the sensor?
 

andrew767

New Member
Hi Andrew many thanks for your fast reply I have attached a picture taken today from the controller I have not been able to get underneath and check if they have been spiced at the sensor end. Will do over the next few days rgds andrew
IMG_20190124_145043.jpg
aaa.jpg
 

ajsellors

A2OC Donor
Hi Andrew many thanks for your fast reply I have attached a picture taken today from the controller I have not been able to get underneath and check if they have been spiced at the sensor end. Will do over the next few days rgds andrew
If you only have 4 wires into the connector then the wires can't be spliced, the connector would have to have been re-used (pins removed and new ones from a different sensor replaced).

Check it carefully though as the wires might have been obscured.

My sensor wires, I unplugged to get a better view:

DSC05401.jpg
 

andrew767

New Member
If you only have 4 wires into the connector then the wires can't be spliced, the connector would have to have been re-used (pins removed and new ones from a different sensor replaced).

Check it carefully though as the wires might have been obscured.

My sensor wires, I unplugged to get a better view:

View attachment 47307
Thank you for the picture and info I will certainly have another look taking the connector apart. Seems the black and grey are missing on my one from earlier inspection. Guess that is why I get no readings from Bank one Sensor? two using the obd data. Very helpful thanks again
 

SLEI

New Member
Is there allways a error code if NOX-sensor or NOX-controller isn't working or can the engine just skip lean burning? I have newer seen AFR-values other than about 13.8 at warm engine and going to 27 when engine braking gas pedal up. I'm fighting with misfire issues and tried every cure found in this forum, maybe my car is in some kind of error mode but don't tell it to me.
My flex joint is leaking between CAT and NOX-box and I bought very reasonable priced aftermarket pipe and while dropping pipes can look also what is going on with NOX.
2004 FSI is driven about 100k miles and the flex part has been allready replaced by someone, bad looking welds can't be factory made.
Don't want just replace NOX-sensor randomly if I even can find brand new sensor. While googling NOX-sensors I found a Finish VW topic where was told that early Golf FSI 1.6 BAD-engine NOX-sensors where faulty but garages still charged 400-500£ for they replacement. Somebody has found a service bulleting about this but still garages charged full price from customers. Obviously I don't want to pay huge money for old stock part which can be faulty from beginning.
A lot of brand new NOX-sensors floating around for 201x engines can A2 sensor be substituded with something else, maybe that has happened above with only 4 wire sensor, lambda part has been dropped out?
 

Rusty911

A2OC Donor
Is there allways a error code if NOX-sensor or NOX-controller isn't working or can the engine just skip lean burning? I have newer seen AFR-values other than about 13.8 at warm engine and going to 27 when engine braking gas pedal up. I'm fighting with misfire issues and tried every cure found in this forum, maybe my car is in some kind of error mode but don't tell it to me.
My flex joint is leaking between CAT and NOX-box and I bought very reasonable priced aftermarket pipe and while dropping pipes can look also what is going on with NOX.
2004 FSI is driven about 100k miles and the flex part has been allready replaced by someone, bad looking welds can't be factory made.
Don't want just replace NOX-sensor randomly if I even can find brand new sensor. While googling NOX-sensors I found a Finish VW topic where was told that early Golf FSI 1.6 BAD-engine NOX-sensors where faulty but garages still charged 400-500£ for they replacement. Somebody has found a service bulleting about this but still garages charged full price from customers. Obviously I don't want to pay huge money for old stock part which can be faulty from beginning.
A lot of brand new NOX-sensors floating around for 201x engines can A2 sensor be substituded with something else, maybe that has happened above with only 4 wire sensor, lambda part has been dropped out?
Interesting to hear your comments on the flex joint, as my two recently acquired FSi's both sound as though they're blowing from that area and both have EML's up.

Anyway, that wasn't why I replied: without wanting to do a sales job on you, are you aware of the Pro-Boost re-mapped ECU available from @A2Steve ?

This isn't a performance map as such, but was developed in Germany to overcome many of the long-standing FSi issues. As you can see in this thread, these were cropping up 'in period' and very much still do. The re-mapped ECU ignores the NOX side of the system as well as leaving the swirl flaps in the open position. It runs the engine slightly cooler via the electronically controlled thermostat (for improved cooling pipe life) and keeps the engine in homogenous mode.

Let me find the link for you, but depending on exchange rates at the time, it's a little under £300 on exchange basis.

At the very least, it's useful to be aware of this option as you might source and replace your NOX sensor only to chase something else, possibly the NOX cat. Again, the Pro-Boost ignores this.

Some have commented on the ethics of disabling systems that were designed to improve cleanliness and efficiency, but the pragmatic reality is many, many FSi's haven't run right for years and have had their EML's lights on as well. The gains from the whole FSi system weren't that great by all accounts, and it's probably the case that a Pro-Boost car will give good, efficient service for years to come (after all, it's still a modern 16V lightweight bodied car).

Here you go:

Ever growing Pro-Boost thread right here!

It's an option anyway, and might work out better value in the long run than chasing 'very FSi' type issues. Clearly it won't rebuild your engine or rescue a failed coil-pack or injector, but if the fundamentals are right, it might just do the trick. Longer term will probably add a bit of value to the car as well.
 

SLEI

New Member
Flexjoint leak is annoying loud after cold start in underground garage but silences little bit after revs get down and sporty roar on road, sound which I had enought in 80's in my MK 2 Escort. I think it was allready leaking a little bit on last MOT but did get clean report.
Mod ECU seems interesting as my NOX isn't going to be high when I get to my goal driving on E85 (0.9£ per liter) . E85=RE85 in Finland cooked from biowaste, Re85 is about 30% cheaper than E598 RON. I have made lot of testing upto about 80% ethanol mixture and FSI low torque feeled like my 1.4TDI chipped AMF with heavy mixture of ethanol.
I have programmed FSI ECU with Unichip.
I don't have anything against flaps if they working, even thought they are called swirl flaps they increase velocity in port low revs and increase torq when they divert flow to port roof and block part of ít.
FSI needs 6 speed also as 3000 revs can't be very ecomical on my road to work.
 

Rusty911

A2OC Donor
Flexjoint leak is annoying loud after cold start in underground garage but silences little bit after revs get down and sporty roar on road, sound which I had enought in 80's in my MK 2 Escort. I think it was allready leaking a little bit on last MOT but did get clean report.
Mod ECU seems interesting as my NOX isn't going to be high when I get to my goal driving on E85 (0.9£ per liter) . E85=RE85 in Finland cooked from biowaste, Re85 is about 30% cheaper than E598 RON. I have made lot of testing upto about 80% ethanol mixture and FSI low torque feeled like my 1.4TDI chipped AMF with heavy mixture of ethanol.
I have programmed FSI ECU with Unichip.
I don't have anything against flaps if they working, even thought they are called swirl flaps they increase velocity in port low revs and increase torq when they divert flow to port roof and block part of ít.
I agree, clearly VAG thought the gains were worth the extra investment at the time. Although I've bought a Pro-Boost, like you my first instinct actually is to try to get it to run correctly as per factory. The tipping point for me will be if the cost of this becomes more than putting in the Pro-Boost.

Very interesting to hear all about the E85, as the FSi's are the only A2's not approved even for our upcoming UK E10 (although happy enough on our E5) so if your car stands up to E85 in the real world for a good period, we can probably relax a bit at the prospect of losing our E5!

@A2Steve started a thread on this matter (which I can't find at moment), and I'm sure your thoughts and experience would be very welcome there :)
 

SLEI

New Member
Is UK E10 95 or 98 RON octane, E10 is 95 in Finland? A2 ECU can compensate a lot with all of those WB lambda sensors but I'm shure there can be some rubber parts which don't like ethanol and major consern is the high pressure fuel pump. I have some bottles of Red line Alcohol Fuel Lube from some old project which I was going to use in straight E85. 1.6 FSI BAD-engine has been used on Golf and VW sedans (Bora/Vento?), Skoda and there is also the early 1.4 FSI which seems to have the same injection pump on head as A2 FSI, all of these should have same NOX-sensor and propably without Audi premium price.
 
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