Audi A6 won't fire when battery less than 12.2V?

Seems about right. The problem is that when you start cranking the engine, the voltage drops even more and once you get to around 11V, the electronics start not being happy.

12.2V is very low. A healthy battery would be at more like 12.5 even on a cold morning.

on 22/12/2009, Doki supposed :

Depends whether that voltage is as measured before cranking, during cranking or after cranking and failing to start. During cranking I would suggest that is high, more than enough to run the essentials and to fire the engine. I would still expect it to be able to fire down to around 10v.

Yes - but most would hope an engine would start if there's enough in the battery to turn it over.

NA diesel landrovers spring to mind as spinning but not starting all too often.

OK, thanks. I have a battery booster in the car and if it happens again I'll use that.

The car hadn't been used for two weeks or so. It started OK just after those two weeks, but not the following morning...

it is quite possible that it is the first warning that the battery is near the end of its life. If it is over three years old then I would seriously consider getting a new one now before it lets you down completely. If it is 'just one of those things' and the battery is recent then at the very least get it fully charged and tested.

Dermit Goldstein submitted this idea :

In that case, first check that it is charging properly. Put a meter across the battery - with the engine running the voltage should usually be a little over 14.0v even with several loads turned on at a fast tick over. If that seems OK, get the battery capacity checked - most places which sell batteries, will do that for free.

[...]

The OP had called out the AA. I would be very surprised if they had not checked the charge rate and battery condition at that time. They have automated kit that does this whilst the patrol sits in the warmth of his van; it produces a printout, so the patrol can't be accused of trying to sell a battery that's not needed.

Patrols make 10% on what they sell, and part of their monthly bonus appraisal is based on such sales.

Chris

those sales are dependent on being able to get a correct battery locally at that time of day/night, they often cannot be bothered (IME)

[...]

As is common with all services, it depends an awful lot on the individual.

Patrols usually carry several batteries and adaptors, covering around 75% of vehicles, although it's doubtful any would have fitted the OP's A6.

Chris

Yes, the AA bloke did check the battery and the charging rate...latter was OK. He came on a motorbike, so no new batteries available.

Had another no start situation this morning...another AA bloke on a motorbike came round...diagnosed no injector pulse...have to get the thing towed to a garage...

Hmm...no injector pulse...any ideas, anyone?

Well assuming the battery's not gone flat then it could be almost anything. Plug it into a FCR.

If it's not firing, no injector pulses. Otherwise all you'd do is flood it.

You mean the lack of injector pulses is a consequence of the no start situation rather than a cause of it?

FWIW it got towed to a local garage this afternoon. They're closed until 4th January, but the gaffer's first impression was that it was an ECU problem. It had been idling quite high (1300 rpm) when it was working.

Thanks to all and a Merry Xmas.

Unfortunately, this generation of Audis has two diagnostic sockets in the relay box which are not compatible with the modern plug used for fault code readers. And apparently the 'adapter' doesn't work too well.

What year and engine? there is a known fault on these cars which causes water to get into the electronics (somewhere under the dash I believe) Repair can be uneconomic.

Dermit Goldstein laid this down on his screen :

I would guess at an ECU failure or maybe the crank position sensor.