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Discussion Starter #1 (Edited)
So, started the car today and I got ABS / Parking Brake / Headlight Level sensor faults. Suspected that these are all linked (they can't all actually go faulty at the same time can they!?), so did some Googling and it seems to be not an uncommon fault, with two main potential causes:

1. Water ingress into an ECU module just in front of windscreen. This causes corrosion and poor / intermittent connections so throwing the faults.
See here - HELP!! ABS/ESP, PARKING BRAKE FAULT AND HEADLIGHT RANGE CONTROL DEFECTIVE!!

2. Faulty ABS sensor or ring on one wheel. Suspect it would be the sensor as the car wasn't moving at the time.

I have had the ABS sensor fault flash up once before a few weeks back while driving, but was gone a few seconds later.

So my plan is to take at look at the ECU to see if the problem is water / corrosion related (though it's not rained here for the last 2 days). The link above suggests that the ECU is on the 'right', below the washer tank. Another thread suggested that on UK cars it's on the steering wheel side. Can anyone confirm which is correct?

If I open the module up and can't find evidence of corrosion or poor connections I presume it'll be an ABS sensor. Trouble is I won't know which one as I haven't bought VCDS yet and was hoping to avoid buying it at the moment while I'm not working. Though I had been waiting for an excuse, just poor timing.

So if anyone knows which side the ECU module is on on a 2009 B8 S5 Cabrio, please let me know. Thanks.
 

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Discussion Starter #2
Amazing... Just started the car to move it onto the drive and all faults have gone.

When the faults ocured earlier the car had been parked in the full sun of a very warm day, and just now when I started it it was in the shade of a cool evening. So I think it's more likely than ever to be a loose connection if temperature has an effect. Will investigate the ECU tomorrow. If I can find it!
 

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Audi 2018 S5, 2007 3.2 TT, 2010 A5
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where abouts are you in the uk, maybe someone has a VCDS lead to assist?
 

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Discussion Starter #4
Thanks for the suggestion jonney, I'm in Wilmslow, Cheshire. I think I should be OK for the moment while I check the ECU for corrosion / loose connections. But if that doesn't turn up anything then access to VCDS would probably be very useful.
 

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Audi 2018 S5, 2007 3.2 TT, 2010 A5
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im a bit far away in Swindon, but if your ever passing your more than welcome to plug it in for a look (keeping social distancing of course). good luck
 
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Discussion Starter #7 (Edited)
OK, so I plucked up the courage to go digging into the ECU connections (messing with the electronics of cars always gives me the jitters).

I should mention that the fault lights had come and gone again a couple of times, usually related to if the car was hot in the sun or cool in the shade. And at the time I did this, it wasn't showing any fault lights. Typical!

So once I'd opened the black plastic box containing the ECU I couldn't find any trace of water. Disconnecting the ECU, I pulled it out and all the pins of the two plugs looked fine. I can only guess that it must just be a loose or poor connection, so decided to jiggle all the relays and fuses.

It was at this point I suddenly realised that I'd totally forgotten to disconnect the battery :oops:

I delved into the boot, removed the spare wheel etc and disconnected the negative terminal as that was the easiest to access. I then refitted the ECU and plugged it back in again. After re-connecting the battery, I fired her up and.....

No warning lights! :D
And phew, I hadn't toasted the ECU by disconnecting it 'hot'.

So I think I've fixed it, but it's a little hard to say for sure. However in the 2 days since then I've not had any warning lights, even with the car in the hot sun. I'm calling that a win.

For those that are interested and in the spirit of sharing knowledge to help others, more detailed steps of what I did are below:

1. I removed the scuttle panel plastic cover which was held with just a screw like fastening at each end and a push clip in the middle that just pulls up with a gentle tug.
2. The ECU is situated on the left side of the scuttle, effectively above the pedal box. It's housed in a waterproof black box secured with 3 T30 screws.
3. I removed the screws and lifted the front of the lid, hinging it up and backward to disengage the lugs holding it down at the back.
4. It was at this point I should(!) have disconnected the battery - This is under the spare wheel and I found it easiest to disconnect the negative terminal (on the right).
5. There's two wiring harnesses / plugs connecting the car to the ECU. You remove them by pulling the clip at the outer end of each, away from the plug. It's quite fiddly for the plug furthest from you as the wiring harness is quite bulky. Once the clip is pulled out, the plugs can be pulled out quite easily.
6. Once the plugs are tucked out of the way you can remove the ECU (if you want) by pressing the black clips on either side and pulling it out.
7. I then jiggled each of the relays and fuses that surround the ECU to make sure they were seated properly and had good connections.
(It was at this point that I actually disconnected the battery - Don't repeat my mistake!)
8. I slid the ECU back into it's mount and reconnected each of the harness plugs. It's a little tricky but with patience you'll know when they're in properly as the clips at the sides press fully inwards, seating the plug the final few mm.
9. I reconnected the battery and fired her up - No warning lights!
10. I replaced the cover of the black box, fitting the lugs at the back first and hinging it down, then replacing the 3 screws.
11. Lastly I replaced the plastic scuttle cover panel. You can just press the screw like fasteners into place and also the centre clip.
 
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