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Waiting for Audi Roadside Assistance (Again!)


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When they left me the yellow ESP traction control light was permanently on. Went for a burn-up, but still on.

The missus, suggested trying the other key - it went out!

Tried the first key again - still out!

Good job I cooked her a Sunday Lunch!

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DieselMeister,

In my opinion the mechanic is talking crap... Charging your battery will make the square root of feck all difference to the root cause of that kind of problem.

Either your charging circuit has got a problem, or the battery is fecked, or the earth strap has got a bad connection. Charging it may get you going for a couple of days but you'll be back to square one when Murphys law applies...

Take your earth lead off where it connects to the car body (get your radio code first) and give it a good clean with a wire brush. If that doesn't do it then its either the charging circuit or the battery itself (they can get deposits on the lead plates inside which limit their cold start capability)

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Thanks a lot for the advice. Most of the guys from the roadside assistance get you mobile again, but they all have different stories.

The last time, the car had not been used for 3.5 weeks, with the alarm etc running.

This time, it was wet, but I'm not sure why didn't start.

Will try your tricks if it happens again. Any ideas where the earthing lead might be located on the A4 saloon?

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169144-ok.gif No worries,

The earth strap chassis connection will be located fairly close to the battery. Just follow the connection from the negative terminal - there will be a thick braided wire with its terminal bolted onto the body. Undo this bolt and check underneath the terminal for any white powdery residue. It should be bright and shiny.

While you are at it, it may be worth checking the battery terminals for the same corrosion. ALWAYS remove the negative terminal first (which is why there is no problem in checking the lead mentioned above), and replace it last. This prevents you accidently shorting a spanner between the body and the positive terminal.

Car batteries are only 12V so cannot give you a shock, but can supply massive current - enough to arc weld a spanner to the body, get it red hot, and cause the battery to quickly produce hydrogen due to the now massive current flow (which would be a bad thing).

Again you are looking for white powder on the battery terminal posts.

If everything looks shiny it is worth just nipping up the bolts on the terminals.

An experiment you could try if the problem re-occurs:

Turn the headlights on full beam before cranking the engine. If they almost go out and the engine has trouble turning over, then the battery needs replacing.

If they remain fairly bright, then the battery is not the problem. Something is amiss with either the battery cabling (which is easy to check) or the starter motor cabling (which is a main dealer job).

Back to the possible root cause of the battery slow-failure. Charging circuits from modern cars with alternators need 2 things:

1. A voltage regulator to achieve the right voltage to charge a 12V lead-acid battery

2. A full-wave rectifier to convert the AC output from the alternator to DC.

It is not unknown for a rectifier to half fail, providing what is known as half wave rectification (as opposed to full wave). This often does not show as a fault but the battery does not receive a sufficient charge rate to keep it topped up, and after a few weeks it will gradually fail. May be worth having a quiet word with an Audi mechanic so no-one loses face if this possibility has been overlooked.

Finally, it may be something simple like a current drain due to an alarm, or tracker, or boot lights are another one... What are you like with a multimeter?

beerchug.gif

Jon

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