Audi S4 won't start

[JohnP68]

I've posted this in the Audi forum but on the assumption that my problem isn't audi specific I've posted it here too.

Tried to start my B6 S4 today, but when I turn the key the engine doesn't turn over and won't start. Electrics seem to be working - including lights - so there is at least some battery power. If flat battery I would have thought the engine would at least turn over a little, but it doesn't move at all. There's not even any sound from the starter motor - no clicking even. Car was working fine a couple of days ago. I've tried the spare key too.

I've got the error codes off using vag.com and there are about half a dozen "supply voltage too low" errors - no other errors though. I've put a multimeter across the battery terminals and the voltage is only about 10 volts.

Anyone got any ideas what the cause could be please, before I get someone out tomorrow to look at it. Cheers.

[Justin S]

with a voltage of 10 volts on the battery, I would say that you have lost a cell in the battery, so need a new battery.

[chimtvr]

I would also suggest a new battery

[JohnP68]

Thanks for all your suggestions. AA man came today and he said the battery was flat. Re-charged and car started fine. Apparently the battery seems ok and is taking a good charge. Mystery is why it went flat in the first place. He said to keep an eye on it, as there may be a leak of current somewhere. Fingers crossed!

[Pigeon]

Start the car, blip the throttle and then hold it at about 1500rpm (doesn't matter if it's more) with some sort of weight on the pedal while you measure the voltage on the battery. If it's around 14V the battery's OK, if it's around 12 you've got a cell out.

[Justin S]

check you havent left the boot light on or something daft like that.