I contacted a couple of distributors here in Germany, including Conrad which is probably the largest electronics distributor, and none of them can get this part which is produced by TE Connectivity. See more on that here in this post about testing the Hall Sensor. I suspect they only sell it to OEMs, so it's not available to the general public.

However there is a repair kit for the Audi A5 which looks remarkably similar, so out of curiosity I stopped by Audi and ordered one Part Nr. 8F0 998 350 for 50,94-Euro. I'll post what it looks like when it arrives next week. It should look something like this. However, since this is for the A5, the rivets are redundant are are not required for the TT.

UPDATE - The Hall Sensor arrived today. Looks exactly as shown below. Additional pictures (link here). The cable length is 36cm.

 

 

Thanks for the video. Have you run a fault scan??

 

I'm starting to think I've connected the pump lines the wrong way round.

Easy to do

 

A video of the pump and lines would a nice to have! ;-)

 

Based on what we know and the photos from Big rex 2 it would seem to me the steps for replacing the F202 Hall Switch would go something like this -

Parts:

• Audi Repair Hall Sensor (Audi A5) PN: 8F0 998 350​

• 2-Wire Micro Clamp Connector (x1)​

Tools:

• Torx T20 bit​

• Small wire cutters​

• Flexible Magnetic pick-up tool (in case you drop one of the screws)​

• Dual 20/22 AWG Cable (0.2-0.5mm²) clamping cable connector (see image below)​

• Loctite® Threadlocker Blue 242®​

• Nylon pry-bars to assist with interior panel removal​

Procedure:

1.) Open and stow the convertible top.​

​

2.) Note - to provide better access to the working area of the Frame, it may be advisable to remove the interior panels behind the seat and below the roll bar.​

​

3.) Release the ball-arm connector from the Roof Flap and snap into place under the Roof Flap. The Roof Flap will default to the vertical (up) position. If needed for additional working space, the entire Roof Flap assembly can be removed.​

​

4.) Carefully insert a towel into the area under the Frame and Hall Sensor. This is to catch the screws or your tools should you accidentally drop them.​

​

5.) Use a T20 Torx bit and unscrew the Hall Sensor retaining screw until the Hall Sensor can be removed from the slot in the Frame.​

​

6.) Use a T20 Torx bit and unscrew the Harness Cable Clamp retaining screw to release the cable clamp from the Frame. This will provide you with some additional slack in the cable and make the next steps a bit easier. Note - Do not remove the cable clamp from the harness.​

​

7.) Using a pair of small wire cutters, cut both wires as close as possible to the old Hall Sensor. The old Hall Sensor can be discarded.​

​

8.) Carefully trim back about 1" of the harness so you can access both Hall Sensor wires for the next steps.​

​

9.) Using the 2-Wire Micro Clamp Connector, secure both wires from the harness to one side of the connector. Note - the wire insulation on the brown and black wires does not need to be stripped back. Follow the manufacturers' instructions (shown below) and be sure the wires are fully inserted before clamping the connector.​

​

10.) Secure both wires from the new Hall Sensor into the 2-Wire Micro Clamp Connector. Be sure you have black to black and brown to brown. Note - the wires on the replacement Hall Sensor are longer than needed. Either cut them to the appropriate length before adding the connector, or simply loop the wires and secure them with a small cable tie.​

​

11.) Reposition the Cable Connector and secure the T20 screw.​

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12.) Position the Hall Sensor into the slot in the Frame and secure the T20 screw. Note - apply a very small dab of Loctite® Threadlocker Blue 242 to the threads.​

​

At this point, it should be possible to close the top automatically. If the top fails to operate check for faults and use VCDS to run the convertible top initialization (link here).

​

13.) Lower the Roof Flap and reconnect the ball-arm connector to the Roof Flap Servo and reinstall the interior panels.​

​

Given the limited space where the Hall Sensor is located, these dual-wire clamping connectors would be an alternative solution to splicing or soldering the connections together. Be sure to get the connector designed for 20/22 AWG Cable (0.2-0.5mm²). These are available from Amazon and other resellers.

Locations of the Hall Sensor (1) and Harness Clamp (2) T20 Torx screws shown from the back of the Frame.

 

@ Big Rex 2 -

If you would be so kind, can you please check your Messages?

I have requested some additional photos from you for the proposed repair. From those additional images, I can put together a more accurate repair guide based on the instructions listed above.

Cheers!

 

Hi
Just completed this repair, without removing the entire roof. I used the part number for the A5 convertible roof repair as it was 1/3rd of the cost of the TT Roadster part. This caused a high level of consternation from my parts supplier...... They were adamant that the part was different. It is. I've enclosed a picture for those of you that fancy a go at spotting the difference.

 

They were adamant that the part was different. It is.

And what is the difference between the A5 part and the TT part...?

Do you have a side-by-side comparison of the two...?

Which one did you replace, the F171 or the F202...?

How did you go about replacing it...?

 

The A5 part comes with pop rivets. The TT harness is held in place by small M5 torx head screws. I assume the A5 is held in with rivets.
I replaced the F202 and it was relatively easy after removing the main securing bolts (on both sides) and lifting the frame clear of the body and supporting with a strap.

 

Ah, okay...yes, they are mounted differently, but the sensor itself is the same.

You didn't happen to photograph the work did you?

How did you connect it...? Did you use the recommended connector or something else...?

 

I wasn't suggesting the sensor was the same. The part is described as a repair kit. Whilst the Audi TT part is described as an actual harness, hence the ridiculous price.

Yes, I did take some photos and no, I didn't use the suggested connectors. As this is a hall effect sensor, a change in the impedance of the circuit is not desirable. In my opinion, a soldered joint is far more reliable, no risk of an impedance change and takes up less room. There was plenty of room to get in with a heat gun.

 

Okay, so soldering is the better way to go. If you could post some pictures that would be great. The Hall Sensors are generally pretty reliable, but we have had reports of them failing from time to time. For the guys in the UK, there's a repair shop that can do it for a reasonable price and his workmanship seems to be pretty good. So for anyone considering this as a DIY, any additional information you can provide would be a welcome addition to the Forum.

I replaced the F202 and it was relatively easy after removing the main securing bolts (on both sides) and lifting the frame clear of the body and supporting with a strap.

I would really appreciate you posting photos of exactly how this was done.

 

Hi SJP
Did you have any luck with being able to buy sensors from the manufacturer's distributor?
I see in the catalogue picture you posted, where the full harness is shown, there are a number of sensors. I'm fairly sure the F171 sensor is the one I've circled and is slightly different from the F202 sensor.

 

SJP.... just seen your post regarding distributers, no luck there then.

However, I have just come across this. Obviously from the same group, VAG, and a couple of years later than my success 2008 TT. However, this does look more like the F171 Sensor that I think is the culprit on her car. It doesn't have the open end for the screw, and it has a locating pin, whereas the F202 sensor has the screw in a forked end and a square block that points at the incoming pin when the roof is up.

If I were to buy it, I'm assuming I could use your proposed bench test to verify that it works?
Do you know if the test gives accurate readings rather than just showing a change in voltage?
I think I read somewhere that the voltages are 9v and 3.5v, so wondering if this sensor might give different voltages and therefore not work?

 

No, I just bought one from an Audi A5. Part Nr. 8F0 998 350. The rivets that come with it are not used for the Mk2 TT.

 

Bonjour à tous.
Grace à ce site, entre autres, j'ai changé le capteur F171.

Afin de m'assurer que ce soit bien le capteur F171 en défaut et non le module J256, j'ai inversé les connecteurs F171 et F202 dans la prise qui est reliée au module J256.(pas besoin de couper les fils, il suffit de les déclipser pour les sortir de leur emplacement)
Fil marron/violet pour F202
Fil vert/rouge pour F171
En inversant, le problème s'est déplacé sur VCDS (il était sur F171 et est passé sur F202). Le problème a suivi le changement de fil donc c'est bien le capteur qui était en

Hello everyone.
Thanks to this site, among other things, I replaced the F171 sensor.

To make sure that it was indeed the F171 sensor that was faulty and not the J256 module, I swapped the F171 and F202 connectors in the socket connected to the J256 module (no need to cut the wires, just unclip them to remove them from their slots).
Brown/purple wire for F202
Green/red wire for F171
By swapping them, the problem moved to VCDS (it was on F171 and moved to F202). The problem followed the wire change, so it was indeed the sensor that was faulty.

J'ai commandé le capteur AUDI A5, c'est bien le même (il est juste dans un support pour le F171).
Pour le changer sans tout démonter, j'ai perçé depuis l'intérieur de la voiture, je ne me voyais pas démonter toute la capote pour y accéder.
Attention, pour ceux qui ont besoin de le changer, il faut faire le trou environ 5mm plus haut et plus vers l'arrière de la voiture (quelques millimètre également).
Il y a un trou sur le support de la capote, l'outil passe dedans puis, capote à moitié ouverte, l'outil va jusqu'à la vis.
Il faut un outil long (au moins 13 centimètres sans le manche).
Pour remettre en place, j'ai pris des pic à brochette que j'ai scotché de chaque côté du capteur de sorte à bien le mettre en place.
J'ai mis un bout de papier autour de la vis et l'ai mise dans le capteur, comme ça elle ne tombe pas pendant la mise en place du capteur.

I ordered the AUDI A5 sensor, which is the same one (it just comes in a bracket for the F171).
To change it without dismantling everything, I drilled from inside the car, as I couldn't see myself dismantling the entire roof to access it.
Please note, for those who need to change it, you need to drill the hole about 5 mm higher and further towards the rear of the car (a few millimetres as well).
There is a hole in the soft top bracket, the tool fits through it and then, with the soft top half open, the tool reaches the screw.
You need a long tool (at least 13 centimetres without the handle).
To put it back in place, I used skewers that I taped to each side of the sensor to hold it in place.
I put a piece of paper around the screw and put it in the sensor so that it wouldn't fall out while I was putting the sensor back in place.

A noter : avant d'installer le capteur, j'ai sorti le fil rouge et vert du connecteur J256.
J'ai branché le nouveau F171 à la place (fil noir), le fil marron du capteur est à mettre à la masse (je l'ai prise sur le crocher de fermeture de coffre, en bas).
J'avais bien le changement de voltage selon qu'il y avait du métal devant ou pas (j'avais également le changement sur VCDS).

Maintenant, ma capote fonctionne nickel

Please note: before installing the sensor, I removed the red and green wires from connector J256.
I connected the new F171 instead (black wire), and the brown wire from the sensor needs to be grounded (I connected it to the boot release hook at the bottom).
I did notice the voltage change depending on whether there was metal in front of it or not (I also noticed the change on VCDS).
Now my soft top works perfectly.

 

Great post, thanks! In the future, would you be so kind and please post in English using an online translator like DeepL. Cheers!

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www.deepl.com

 

A big thank you to all who contributed to this thread.
I have just repaired my F171 Sensor, using the Audi A5 sensor.
Apart from numerous days reading these forums, looking at the top, the sensors and a bit of fiddling, it had taken me about 6 hours.
I did the whole thing in situ and most of the time was spent trying to access the screws to both the sensor and the cable clamp.
I manually opened the roof to about the 3/4 position, then shut off the hydraulics in the boot and used 2 peices of wood to brace the scissor frame.
I then removed the pivot pin from the piston and lifted it up slightly, holding it with zip ties, to give me a bit more room to use the special little ratchet that I'd purchased.
I did buy a special tool off Amazon.

Which as you can see, I modified to access the cable clamp by adding a pivoting extension, along with cutting down a T20 Torx bit.
I replaced the sensor by soldering the new one into the old wires.
I've had a couple of thoughts along the way.
Firstly, as shown in Yoyoyo17's excellent post above, the sensor is the same as the F202 sensor, but it's held in a holder.
I removed this whole fitment and trying to edit the screw when assembling was one of the hardest bits. Looking at it, I'm now sure it would be possible to simply slacken the screw, as for the F202 sensor and then find a way to sorting the barbs that hold the sensor onto the holder, ( again see Yoyoyo17's photos. This would then mean assembly is simply a case of pushing the new sensor into the holder and tightening the screw. Much easier than trying to relocate the screw.
Secondly, although I was quite lucky in getting the screw on the cake clamp to locate, I was quite prepared to have held it in place with a zip tie. I don't think it would have been detrimental to the operation of the hood.
Hopefully this will be of use to others.

 

Nice one! I actually have that exact same mini-ratchet so looks like if my Hall sensors fail, I already have the right tools on hand!