festamb1 Posted April 14, 2022 Share Posted April 14, 2022 Hi I have 2010 Audi A4 TDI 143 BHP which has a charging issue at present the warning light came on a couple of days ago saying the car was not charging but once I re-started the car this had cleared then an amber light came up saying low battery, I have checked what I can under the bonnet so there is a fan belt on the alternator and I have just under 15 volts coming from the alternator but when I check the power on the junction box under the windscreen that's for jump starting the car I only have 11.4 volts and this is with the engine running and not running this don't change as the cable from the alternator goes to the starter motor then up to the jump start point in a single solid cable I should see I higher voltage on the jump start point. The car has always turned over slowly most of the time but always starts even on cold mornings I do have some sort of earth problem on the car I think as some times when I put on the indicators I get a static noise through my radio weather this is part of the charging issue I Don't know. Many thanks Mark Quote Link to comment Share on other sites More sharing options...
Steve Q Posted April 16, 2022 Share Posted April 16, 2022 You've done a good amount of diagnostic work. I'd still advise a diagnostic check to see if there's any fault codes. I'd still advise getting the battery tested to see if it's failed too. Quote Link to comment Share on other sites More sharing options...
festamb1 Posted April 17, 2022 Author Share Posted April 17, 2022 Hi it is a new battery and there are no fault codes at all when I scan the car I think there is an issue with the wiring loom from the alternator to the starter motor Quote Link to comment Share on other sites More sharing options...
Magnet Posted April 17, 2022 Share Posted April 17, 2022 Hello Mark, Apologies if these are daft questions, but does your model year require an AGM battery, and if so is that what you have fitted? I raise this since sometimes owners simply replace like for like with what was currently there. Not good practice since a nice previous owner may have retained his near-new battery when selling, and put an old anything-that- fits battery in its place. Also make of your new battery? Having said all that, your theory sounds worth investigating. Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
festamb1 Posted April 17, 2022 Author Share Posted April 17, 2022 Hi I put a new battery on the car when I got it as I noticed it always turned over quite slowly so I fitted the biggest rated battery that was listed for my car Yuasa HSB019 Silver 12V Car Battery 5 Year Guarantee the car still turns over slowly most of the time as the battery is in the boot and I am at time not getting the right voltage at the jump start point under the front windscreen but the alternator is giving out high 14 volts Quote Link to comment Share on other sites More sharing options...
Magnet Posted April 17, 2022 Share Posted April 17, 2022 Many thanks Mark. Do you know if your model is on an ‘intelligent’ charging system which needs an AGM battery? Sorry, I’m not sure. The fact that the battery is in the boot, should not practically affect the enthusiastic nature of how the car ‘turns over’. Audi would obviously not have designed the car with that issue. If this were mine, I would be double checking that the battery is of the correct type, and not simply the biggest that fits, and as you say, carefully inspect all wiring ( and earths) associated with the starting and charging systems. Although 14.0 volts is slightly below the mid 14s I would expect, it should be adequate - all else being as it should be. Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
festamb1 Posted April 17, 2022 Author Share Posted April 17, 2022 Hi The battery I have fitted is listed for my car I have checked on different site when I purchased it I am getting between 14.8 and 15 volts on the alternator so I would say this is working fine some time all I get at the jump start point on the windscreen scuttle is 11.4 which I checked the battery with the engine off and this all the battery had left in at the time considering the cable that comes from the alternator goes to the starter motor then up to the jump start point I should be getting a lot more than 11.4 volts as this is a solid cable that connects to the start then from the starter motor goes up to the jump start point so I think there is a break in the cable as this fault is intermittent I just don’t think my battery is getting enough power to keep it charged as the power from the alternator is intermittent Quote Link to comment Share on other sites More sharing options...
Magnet Posted April 17, 2022 Share Posted April 17, 2022 Is that 11.4v (effectively at the battery) with the engine running then? If the alternator is putting out 14.8 to 15v then little to worry about there. Poor connections twixt the two?? Break in the cable = no continuity = no charge/ no current through cable. Test:- Measure the static voltage at the battery and make a note of it. Charge the battery overnight and measure the voltage again and make a note of that. Leave the battery connected ( with the car unused) for the rest of the day, and measure the voltage again. Should be as near as damn it to the early morning just-off -charge voltage. If not - problem! Test this system for a parasitic drain, once you are sure all cable and earth connections are sound and serviceable. Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
festamb1 Posted April 17, 2022 Author Share Posted April 17, 2022 Many thanks Gareth Quote Link to comment Share on other sites More sharing options...
festamb1 Posted September 28, 2022 Author Share Posted September 28, 2022 Hi this problem above sorted itself out until yesterday As of yesterday the car has been fine but yesterday the battery warning came back on again so I have down a lot of diagnostic's and this is what I have found I have 14.5 to 15 volts at the alternator with the engine running at the junction box under the windscreen (with the jump start terminal) I have 11.9 volts even though the cable from the alternator goes to this junction box this is also with the engine running. with the engine off I get 11.9 volts on the rear of the alternator and I get the same at the junction box under the windscreen. if I run the engine and disconnect the cables that comes from the alternator at the junction box and test it once disconnected I get the same voltage as what the alternator is giving out but as soon as I connect this to the junction box the voltage drops to 11.9 volts. There must be something cutting off the voltage once I re-connect the alternator cable some sort of over voltage cut-out as this don't make any sense otherwise has anybody got any knowledge of this please the car is a 2010 a4 TDI Many Thanks Mark Quote Link to comment Share on other sites More sharing options...
Steve Q Posted October 2, 2022 Share Posted October 2, 2022 Hi Mark, there's no aftermarket add one to the car are there? If so sometimes the installation of these accessories can be dubious. Quote Link to comment Share on other sites More sharing options...
festamb1 Posted October 2, 2022 Author Share Posted October 2, 2022 Hi Steve no there is nothing like that on the car at all there there must be a sensor or something that cuts the alternator loom if it thinks the car is over charging thanks mark Quote Link to comment Share on other sites More sharing options...
Man le-mans1 Posted January 22, 2023 Share Posted January 22, 2023 Hiya just seen this post and I have the same problem.. 14.50-14.80 volts at the alternator and 12.60 ish volts at the battery and the +in the engine bay by the scuttle. just seeing if you managed to sort the problem thanks Quote Link to comment Share on other sites More sharing options...
festamb1 Posted January 22, 2023 Author Share Posted January 22, 2023 No not yet look at the battery overload at the rear of the battery in the boot this cuts the power off if the voltage is too high I think this is the problem Quote Link to comment Share on other sites More sharing options...
Man le-mans1 Posted January 22, 2023 Share Posted January 22, 2023 Thank you I will have a look tomorrow morning Quote Link to comment Share on other sites More sharing options...
Man le-mans1 Posted January 22, 2023 Share Posted January 22, 2023 (edited) I’ve just been given this advice on another forum which may also help you. Engine running, A: Measure the voltage from the alternator B+ post to the alternator housing. B: Measure the voltage from the positive jump start post to the negative jump start post. C Then measure the voltage from the alternator B+ post to the positive jump start post. D Then measure the voltage from the alternator housing to the negative jump start post. If A and B are not nearly the same, then the difference should have been measured as either C or D. C and D should have been near zero. But if one is greater than zero, then that cable path is corrupt. I had a 1V drop from alternator B+ to positive jump start post and replaced my alternator output cable, which routes to the starter and then to the TV22 (the distribution block with the positive jump start post on it) with a new cable direct to the TV22. I made a thread about it in the B8 A4 forum on audizine. Edited January 22, 2023 by Man le-mans1 Quote Link to comment Share on other sites More sharing options...
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