Thanks yes, I'd read that post before but couldn't remember was it here or Audiworld with the petrol engines. I have that PDF but as often is the way, sometimes a job can be done easier when not following the manual to the letter so I hadn't even consulted it. Thanks for the help.

OK, so my issue is getting curiouser and curiouser...mechanic tells me the PS pump is gone and rack is OK, but I now also have a battery not getting charged issue along with either the fanbelt or one of the pulleys fouling something where the mechanic is wondering if the engine mount(s) have allowed the engine to move forward slightly?? I'm really wondering how all these issues came about at the same time but mechanic tells me there's nothing wrong with the belt and no pulley is seized. I'm going to replace the PS pump to start with...

I never seen PS pump fail in such a way. Usually they either become noisy or start leaking. You have several issues that all point to belt drive. You say belt is still in place so maybe it is slipping. Have you or mechanic checked crankshaft pulley? It's 2 parts steel connected by rubber for vibration dampening. It's common failure point not just for Audi but many diesel cars, happened to missis Q7 3.0TDI and also friends A6 3.0TDI. Usually the rubber splits or becomes detached from steel and outer part just falls off but I suppose it might be possible that it stays in place just slips around. When there is little load, low rpm it might be turning belt but as load increases it just slips.

Maybe get another mechanic for second opinion.

I have attached the pictures of failed pulley from Q7. 1 both parts together and then separated

Thanks for the input. Yes indeed, the belt would tie all my issues together and although I haven't seen exactly what the mechanic is talking about as regards the fanbelt getting fouled, a crankshaft pulley failure like you describe may be causing the issue. As regards the PS pump itself - It had been 'moaning' intermittently over the past year or so, so I wasn't sure if it was the rack or the pump. I'll go back to the mechanic and try and get a proper look at what he's describing. He's adamant the pump is not working as he sees no fluid disturbance at the reservoir when he activates the pump.

Great call.
Had a look with the mechanic today and it's the crank pulley that's going in and out and fouling a metal pipe that runs behind the radiator. The belt and all pulleys spin away no problem until the steering wheel is turned and then the belt stops dead.
With these pulleys known for failing, does anyone know of any improved upgrade on the original?

Don't know of any aftermarket improved versions, but according to the parts catalogue, yours should be part number 059105251AD. It has been superseded several times, but it depends on specific PR codes, all relating to 'vehicle class'.

PR codes: 0HP,7JV
Most recent (2016) part # 059105251DJ

PR codes: 0CS,0HV,1CH,1CN,1CR,1CW,1CX,7JL,7JM,7JU,7JW,7KJ
Most recent (2018) part # 059105251DL

Yes they are known for failing.

There are revised versions, not sure if they are any better. I do not remember which one I had on Q7 but it was newer version than what it would have had from new but not the latest, genuine Audi item and still failed. I don't know how long it was replaced before. I think they are about £350 from Audi and aftermarket start from £60 if you are ordering from abroad and prepared to wait and can go up to the same £350 for aftermarket as well.

I got Febi aftermarket on eBay from UK for £100 as I did not want to wait for shipping from abroad. Also did not want to pay £350 for OEM as they are known to fail anyway and plenty of space on Q7 so pretty easy to change if it does not last as long as OEM and I need to change it again. A lot less space and harder to change on A6, not sure what it's like on A8 but if it's fouling a pipe and not falling off the I guess not as easy as on Q7

Thanks for the info Steamship. Yes I got that same part number from an online catalog and although I've not seen the actual part on the car, I've no reason to think it's incorrect. When I entered it in the search at https://www.oemvwshop.com/059105251dj-flywheel-p502770/
it came back with the same DJ suffixed updated part number that you quoted above, although I'm a little concerned as I only see Audi A8 up to 2007 mentioned. Then I also see that 059105251DL is listed for post 2010 cars only. Strange that the FL D3 is omitted from both lists.

Yes, I'm looking to go with genuine if there's no other upgraded part available, as it's front off to change it, so no small job. I'm going to replace the belt also and see if there's anything else I can do as well while I'm in there. Just in time for Christmas!!... :rolleyes:

From the official parts catalogue:
AD was available on the A8 from '04-'10

I was a bit vague with the DJ and DL ones in that the dates I gave is when they became available i.e. superseding older parts, but they won't necessarily show up in online searches as being suitable for an older vehicle.