Alternator light

devans

Member
England
I have the alternator light on the dash it’s not very bright much less when the car isn’t running. The photo shows it brighter than it looks . I’ve measured the voltage with the car running and when not running it looks good to me. The alternator looks fairly new so does the battery. Nothing in VCDS either.



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Not running



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Car running


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Voltage running

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Car not running
 
Evening David,

Im no expert on there things but if your battery is good then it might be worth testing the voltage nearer where the fault/notification is, in this case the instrument cluster not reading enough power. Instead of at the battery, check the voltage at the instrument cluster (Fuse 1: 10a) and the earthing point at the A pillar. If you get very similar readings as you posted above then I’m out of ideas.

If there is a significant difference in readings then this would point to the vehicle harness somewhere which is beyond my knowledge at this time.

You could also test the voltage at the large fuse within the passengers footwell compartment along with the the earthing point in the A pillar.

Hope this narrows down your issue.

Kind regards,

Tom
 
Another quick and simple check is to ensure that the battery terminals are clean and tight and the auxilliary positive box is secure to the positive clamp and its internals are clean with a good tight contact.
 
I reading from fuse 1
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Reading in the boot

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Battery is fairly new .terminals all look good and tight.

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I’m going to swap the battery over see if it makes a difference
 
Battery swapped no difference. I have a spare alternator to that’s the next thing I can swap over but that’s a bit more work.
 
Did you check the auxiliary positive box?
All tight and look good .

It’s been great the past 3 months. I replaced the stater motor and fitted a new lead between the starter and the bolt behind the light as it was slow to start that was 3 months ago. I’Ve had the car nearly a year now.
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Sounds more like you have a wiring issue somewhere, either a corroded plug or damaged or loose wiring. How good is the alternator belt, tensioner and over run clutch? Does the light only just come on at idle or at any rpm?

Remove the plug for the power steering and check that for corrosion as it is one of the biggest electrons consumer.
 
Belt and tensioner look good. Like they were replaced recently with the alternator. Can’t see any corrosion all cables look good . Light stays on when driving or stationary . I would have no idea there is a problem apart from the light on the cluster. I’ll have a look tomorrow at the power steering plug.
 
What does VCDS state the battery voltage as? Do you have any aftermarket items fitted i.e. non Audi radio, bluetooth adapter Dab radio etc?
 
Not looked at VCDS I didn’t know I could get that from VCDS. Will have a try tomorrow

I have RNS-e Audi hands free ,MFSW and AMI all been in since I got the car. No issues with these so far and have the same setup in my other A2.
 
Just trying to work out if something may have been incorrectly wired or some other wiring dislodged in the process.

Measuring blocks in VCDS can reveal far more than you would expect. It is how colour DIS has all these extra measurements available.
 
Did the alternator light problem come on on its own, or related to other events like changing alternator etc?
 
Tried removing the alternator but I can’t get the tensioner to lock in position job for the garage now.
 
Again nothing to lose... The terminals are corrosion free on the back of the alternator and the big positive lead undamaged and has a nice tight connection? The small electrical plug also could have pin or wire corrosion. It is the correctly rated alternator for your car?

A 2005 tdi would have a 140A alternator. If it is more than that then the system could be picking up OVER CHARGING
 
It’s a 140amp alternator . Bosch alternator I’ve checked all the connections they are good. It’s pretty good under the bonnet no signs of corrosion anywhere. Leads all good as well.
 
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