Nox Sensor replacement instructions 1.6FSI

chb

chb

Well-Known Member
Since there is very little written on this, I thought I should share my experience with the forum.
First the bit for Google to find:
This is for the Audi A2 1.6FSI mine is an 03 plate with the BAD engine.

The fault I had was the engine management light coming on and staying on.

A scan with VAG-COM picked up the fault as :

17446 - Heating Circuit for Nox Sensor: Open

The cure is to fit a new Nox Sensor, part number P A8Z0 906 261

Cost for this part from Audi (jan 08) was £122.96 inc vat.

This job is fairly easy to do, but needs a bit of manual dexterity to get the sensor out and to remove the lead from the passenger footwell.
 
The sensor itself:

OK so you buy this and open the box, what do you get?

Well the sensor looks like a spark plug and screws into the exhaust system just behind what looks like the cat.

The sensor has a leed permanently attatched to it. At the other end of the leed is a plug that fits to the Nox sensor controller.

The leed comes with a rubber grommet permanently fitted to it, to seal the floorpan of the car.

The plug has a panel clip pre-cable tied to it. This clips to a plastic plate inside the passenger footwell. There is a lead from the Nox sensor controller that then plugs into the sensors plug.
 
Start in the Footwell:

OK open up the access panel to the passenger footwell.
For this I assume you are working from outside the car, leaning in through the passenger door opening. So left is towards the footwell, and right is towards the rear. Top is near the gearstick and bottom is nearest the sill of the passenger door frame.
The nox sensor controller is a small box, in the bottom right. Two leads come out of it. The right hand one is clipped to the sensor and is secured to the car with a plastic panel clip.

With a flat bladed screwdriver to help, unplug the sensor.
You should be left with the sensor plug left cable tied to the plastic plate.
Snip the cable tie to free the sensor.
Pry the panel clip free, do be careful as mine disappeared into the bowels of the footwell and is still in there. Your new sensor comes with this pre attatched, so you don't need it!

If you follow the route of the sensor lead you will see it ends up at a rubber grommet in the top left of the compartement.
The lead is VERY short, so you need to route it efficiently.
It also threads through a very crowded area, with lots of exposed teminals. So you need to note the route of the lead and also be careful not to short anything out as you maneuver the lead.
 
Under the car:

OK under the car you will find a plastic cover that shields the grommet.
The plastic cover has three hex nuts. I removed the one to the rear, and loosened the two nearest the front, so that the plastic panel could be angled down to gain access the the grommet.
Lever the grommet out (ie don't push it into the footwell compartment).

You can then fiddle with the lead from inside the footwell to get it out through the grommet hole.

You should now have the plug out from inside the car.
From underneath you will see that the plug dissapears round the textured Aluminium heat sheild, and reapears at the sensor. Are your feeling dexterous?
 
Removing the sensor:

oh, forgot. The sensor lead clips onto Alu heat sheild edge, pry open the sprung clip and remove the lead. DO NOT TRY to remove the clip from the ALU heatsheild, it does not want to come off. The clip itself is spring steel, and its actually quite easy to get the lead out when you realise which bit to lever open.

I sprayed a bit of WD40 on the sensor screw thread and left for half an hour to penetrate.

I used my big BAHCO adjustable to remove the sensor so am not sure of spanner size needed. It is bigger than 19mm though (my biggest open ended spanner!).

Before you remove the sensor, you will need to lower the heat sheild to get a bit more space behind it.

The heatsheild has 6 funny looking pressed alu nuts. You will need a suitable size socket to get these off. With these removed, lower the heatsheild by the inch or so permitted by the exhaust.

Now unscrew the sensor from the exhuast, you can practice twisting the lead from the plug end to stop the lead twisting up as you unscrew the sensor.

The needs to be removed through the apperure in the heat sheild, and manuevered round the back of the heat sheild and out. This is the most fiddly bit of the opperation.

You should now have the sensor completely removed.
 
Refitting is the opposite:

OK just follow the insructions backwards to fit the new sensor.

Fit the sensor first, makeing shure not to twist the lead.
Clip the wire to the heat sheild
Push wire through the floor pan

etc
etc

Fault code will clear itself, though only after a few trips.
 
Thanks for this chb. Mine was replaced under warranty yesterday - but it'll be useful to know how to fix it next time.

Ben
 
NO worries.
I thought I would post it up, cos the job is definately a DIY task for anyone with the right gear (spanners and ramps) and inclination.
Also there were a few moments when I thought...oh poo.

First was when I unscrewed the old sensor and pushed it up through the hole in the heat sheild and watched it disapear out of view. I had one of those "what if its wedged there moments"!

The other real worry was when it took 24 hours for the car to realise a new sensor had been fitted and turn of the engine fault light.
 
Also useful, can people post age, milage that they have replace nox sensors at so we can establish a "normal" lifespan for this component. For a start my 1.6fsi car is 4.5 years old and has done 34000. This is it's first nox sensor.
 
Hi guys, my 2002 FSI with 125k kms seems to have the same problem.
I just bought the car last week from another guy and when I came back home, after the scan, I had this 17446 fault code.

I actually do not have any sort of light on the dash, nor seem to have any problem in driving.
I also tried to calcel the error, but it is still on, which presumibly means the issue is still there.

Could you please which are the troubles occurring with this fault?

Since I am a kind of dummy on this aspcet, could you please tell me what does this fault code mean? Do it as you were explaining the thing to a 2 years old baby.. :)

I actually hear a sort of real "diesel" noise when I turn on the engine, for half a second .. some other times this noise is replaced by a kind of "horse" moan.
Your help, as usual, is muchj appreciated.
 
Hi, glad you found the guide useful.
The "diesel sound" you get with the FSI is perfectly normal. It's normally first thing on a morning and only lasts one or two seconds while oil gets to where it needs to!

Someone more knowledgable on VAGCOM than me will say for sure, but if your fault only came up on a scan then it may not be a problem.

When my Nox sensor went I DEFINATELY had a permanent light on the dashboard.

If there are no lights on the dash, and if the car runs OK and has good MPG then I would clear the fault and leave it.
 
Just noticed that the thing won't let you reset the fault code.
This puzzles me, because I think if this is so then you should have a warning light on the dashboard (unless bulb has gone/removed?).

When my Nox sensor went, the car drove fine, so this will not really help you diagnose. I fixed mine straight away, so did not have chance to assess effect on fuel usage. I would expect a faulty nox sensor to cause the car to use a little more fuel. As you have only had the car for a week, you won't know what normal fuel usage looks like so will probably find this hard to assess!
 
Thanks.
Actually I experienced some 12,5 km/l around town and 14,5 - 16 on motorway (between 120 and 140 km/h), which seems to be very reasonable, compared to average fuel consumption I did read on the web.

The option for which the previous owner might have disconnected the bulb in the dashboard, although it scaries me, seems to be a very cheap solution .. eheheheheh..

Hope he did not go for this option though..

In my Italian forum I am currently in touch with the owner of an Audi Service (one of our moderators), who is trying to sort the issue out (although he does not have the chance to see the car personally, due to the distance).

I'll keep you informed but, please, should you have additional infos, please do not hesitate to post them here, since they are much appreciated.
Gianluca
 
turn off disable/nox sensor in vag com?

Hi,

mine been gone for almost a year - car is fine, just passed MOT. Engine on dash is still on though, and if I reset it, it just comes back on again.

Is there anyway we can just disable the warning light on it, as it's obviously not that big an issue?
 
I have a 1.6 FSi it has done just over 20,000 miles on an 04 plate. I was advised to replace mine when the light came on at 10,500 miles! I haven't got round to doing it yet as a)There has been no noticeable drop in performance or economy B) It makes no difference to the MOT and C) the stealer wants over £300 to do it!!
 
Just done mine, was a little tight for my hands, but replaced, with help of this thread

1.6 FSi, Nox sensor replaced 70,110 miles

Thanks
Alan
 
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