Hi team hoping you can help with a problem on my A3 convertible.  Sometimes when I turn the key to start the car nothing happens. The dashboard lights come on as expected but there is no sound from the starter. I can turn off and on again - still nothing or might start. Third time it starts as normal .  Then days go by with no starting problems at all.    
Battery was new last year and checks out as fine.   Any ideas what might be going on?

thanks

I'd recommend a diagnostic check to see if any fault codes flag up. Could be a crank sensor. 

Is there any red light on the dash which could indicate an issue with the imobiliser? 

Thanks Steve. I should have said no fault codes show up on OBD. 
I wondered about the immobiliser but no red light on the dash.

Odd there's no fault codes. When was the car last serviced. Could it be an issue with the HT leads or spark plugs for example 

It’s serviced by Audi in July every year. It’s the intermittent nature that’s odd. I did a 400 mile round trip recently with lots of stopping and starting and this happened only once. 

Hello Alan,

Check connection on to starter motor solenoid.

Thanks. I think when the weather warms up a bit I need to get my head under the bonnet and do as you say.

Just an update. I still can’t find what the issue is and the car has recently behaved itself so I will get it looked at next service,

I know its not the same car, but I had a similar issue on my XKR. It turned out to be a bit of corrosion on the ground cable from the battery to the car body. I just removed the cable, cleaned with wire brush & reconnected and not had a problem since. May be worth a look.

Thanks Kev. but beware of disconnecting Audi batteries, and the potential need to re- code after. 
Over on the Jaguar forum, there seems to be opinion that JLR systems don’t need recoding after fitting a replacement battery, but….

6 minutes ago, Magnet said:

Thanks Kev. but beware of disconnecting Audi batteries, and the potential need to re- code after. 
Over on the Jaguar forum, there seems to be opinion that JLR systems don’t need recoding after fitting a replacement battery, but….

Your right, they certainly don't on the older jags. Would it be possible to connect a battery charger to an alternative ground point to try and kid the car that the battery is still connected.

I haven’t removed the ground point but have looked at it and it seems pretty sound - but it’s worth another look noting the coding issue. Thanks guys.