Having an issue and hoping someone could provide some wisdom, have tried a search of the forum and whilst I found an identical issue on the forum from 2019, unfortunately the poster doesn’t say if they found the solution/problem.
My issue is the son’s car (A3 8P 2.0 TDI) was working perfectly when parked up the previous night, came out to start the next morning and all normal until turning ignition on, instrument cluster failed to light up (radio/CD illuminates though). Crank car and starts immediately however cuts out after 2 seconds (guessing not getting immobiliser input), further checks show electric windows also not working but everything else (lights etc working). New battery fitted 2 months earlier and all fuses seem to check out okay. 
Any advise greatly received or knowledge of a good mobile auto electrician who covers Fife (Scotland) would be appreciated 

Edited February 16Feb 16 by Tugg
More detail

37 minutes ago, Tugg said:

Having an issue and hoping someone could provide some wisdom, have tried a search of the forum and whilst I found an identical issue on the forum from 2019, unfortunately the poster doesn’t say if they found the solution/problem.
My issue is the son’s car (A3 8P 2.0 TDI) was working perfectly when parked up the previous night, came out to start the next morning and all normal until turning ignition on, instrument cluster failed to light up (radio/CD illuminates though). Crank car and starts immediately however cuts out after 2 seconds (guessing not getting immobiliser input), further checks show electric windows also not working but everything else (lights etc working). New battery fitted 2 months earlier and all fuses seem to check out okay. 
Any advise greatly received or knowledge of a good mobile auto electrician who covers Fife (Scotland) would be appreciated 

Hi the first to do would be to get the car scanned for faults this should throw up whatever is not connecting that will also show if the can gateway is mucking about, it could be anything from immobiliser problems to a start position sensor if auto or clutch position sensor if manual, I have also known this type of problem where previous owner has not had all the software updates done, sorry about the thread that led nowhere we often get that on here, ask any of the moderators on here, its so frustrating as the poster gets the right answer and then promptly clears off.

Steve. 

Appreciate your reply Stevey, I should have mentioned that I scanned it with my OBD11 and there were loads of codes (Anti theft, doors, brakes and airbag to name but a few) which pretty much all related to not being able to communicate with instrument cluster. This obviously points towards cluster, but just wanted to hear from anyone experiencing same issue as I’ve been led down rabbit holes before following codes!

29 minutes ago, Tugg said:

Appreciate your reply Stevey, I should have mentioned that I scanned it with my OBD11 and there were loads of codes (Anti theft, doors, brakes and airbag to name but a few) which pretty much all related to not being able to communicate with instrument cluster. This obviously points towards cluster, but just wanted to hear from anyone experiencing same issue as I’ve been led down rabbit holes before following codes!

Hi you could try disconnecting the battery positive for an hour and then see if it resets  but the only time I have ever encountered this before was when the battery was failing therefore might be an idea to check the battery voltage static with every thing off then try it with everything on and see what happens with the static voltage, anything around eleven volts means it is probably on its way out, the way it works is if  the battery won't hold a steady current the system closes anything that should work while the car is asleep is classed as a parasitic drain so it gets shut down, yes its had a new coded battery but you did not mention the brand also factor in battery life [how long is a piece of string] and you have a possibility rather than chasing codes.

Steve.

Good to have suggestions coming in and validating my efforts/thinking so far. The Battery is a AGM096 and a like for like replacement, tested at 12.67v before trying the battery disconnect/reset yesterday, after drawing a blank with loose wiring/fuses. Think I’ll have to try running diagnostic on the cluster next, will keep this post updated on my progress and hopefully eventual solution. 

Edited February 16Feb 16 by Tugg

20 minutes ago, Tugg said:

Good to have suggestions coming in and validating my efforts/thinking so far. The Battery is a AGM096 and a like for like replacement, tested at 12.67v before trying the battery disconnect/reset yesterday, after drawing a blank with loose wiring/fuses. Think I’ll have to try running diagnostic on the cluster next, will keep this post updated on my progress and hopefully eventual solution. 

Hi worse way you will have get the cluster out and send it away somewhere to be tested.

Steve.

Martyn I disconnected the battery for an hr as part of the initial repaired/fix but had no joy.

However after reading your comment I thought I’d try reconnecting the Cluster which I’d removed 2 days previously ready for sending off for diagnosis/repair, as it’s only a 5 minute job to replace as you know.

Anyway long story short Cluster is now back fully working and car fully operational, so well worth the 5 minutes, so cheers for taking the time to reply to my query of your post from 2 years ago

Will update post again in 3-6 months and make as solution, unless I need to reply earlier should the fault return.

Edited February 18Feb 18 by Tugg

Just to update this thread/post, it’s now been 10 weeks and the issue has not returned since the fix of disconnecting the cluster overnight.