Touareg broke, advice sought.

[Borla]

My uncle has a V6 diesel Touareg, c2008. He's had it for about 2 years without any problems. Tried to start it Friday morning and it wouldn't start, battery didn't have enough juice to spin it over (his one has the single battery under the passenger seat). Battery was replaced about 6 months ago, this car doesn't need the BEM info setting that the later cars need.

Battery was put on charge, in evening car started OK and ran for about 5 mins then suddenly cut out, dash dead, no lights, nothing. At this point he phones me. I go over there the next day with a dvm, we pull another known good battery from his pick up and put it in the Treg. With dvm on the battery we start the car, after engine starts dvm reading goes from 12.5v up to 13.8v briefly before sharply dropping to about 5.8v at which point engine dies. Again, dash is dead. Pulled neg lead off battery and there was a fair sized flash, so something is drawing a big chunk of current, enough to pull the battery plus alternator voltage down to a point where the car cannot function. It isn't the battery because as soon as the lead was removed the battery was back to 12.5v and after 5 minutes of head scratching we gingerly reconnected it without problem and the car started again, this time without stopping. We have put VCDS/vagcom on it and there is a list of fault codes as long as your arm, but most of these seem to be linked to the low battery voltage, nothing else jumps out. Starter motor sounds fine, spins engine over well and there are no weird noises or smells when engine cuts out.

Anyone got any ideas please? Any pointers gratefully received.

[stevieturbo]

Given potential for damage, you may be wise seeking professional advice.

Check all big power wiring for potential shorts, starter motor, alternator etc If that wire is damaged anywhere it could cause major problems.

Likewise bad earths can cause all sorts of issues.

Perhaps connect up a battery remotely via a couple of decent sized fuses ( just to diagnose, not start the engine ) and monitor current draw just to see if anything odd is happening. Probably need a current clamp meter for that

[George111]

Have you had the alternator checked ? That if faulty could possibly cause your symptoms.

[Stiggolas]

We had something similar on my dad's 2004 Merc C270. Turned out to be the engine block heater which was intermittently shorting. Took us a while to find that one as we didn't know it had one!

[Borla]

Stiggolas said:

We had something similar on my dad's 2004 Merc C270. Turned out to be the engine block heater which was intermittently shorting. Took us a while to find that one as we didn't know it had one!

Thanks for the tip, just done a quick search and Tregs don't have an engine heater :-(

[imagineifyeswill]

As has already been asked have you had the alternator checked, with your symptoms that would be my first port off call.

[Sheepshanks]

Borla said:

Stiggolas said:

We had something similar on my dad's 2004 Merc C270. Turned out to be the engine block heater which was intermittently shorting. Took us a while to find that one as we didn't know it had one!

Thanks for the tip, just done a quick search and Tregs don't have an engine heater :-(

Funnily enough I have a C270 but we also have a Tiguan and that has a chunky electric heater. As far as I know pretty well diesels have them, otherwise they'd never warm up in cold weather. As the poster above suggests, a lot of people don't know they're there, and info is hard to come by (in the Merc it's in the cluster menu though - can't remember on Tiguan).

[Borla]

I've done a couple of www searches and found no hits for block heaters on the V6.

Alternator is coming off this weekend and getting checked out, cheers all.