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Alternator charging issues

Discussion in 'A4/S4 forum(B5 Chassis)' started by PAULF, Mar 6, 2013.

  1. PAULF
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    PAULF Active Member

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    [Mar 6, 2013]
    I am having issues with the charging system on the Avant (2.5TDi Q) that appear to have been ongoing for a while!

    When I start the car, the battery voltage stabilises at about 12v(reading the dashboard ammeter) for a couple of seconds, and then comes up to 14v. The time it takes to come up varies, from a couple of second to a few minutes. If the voltage was below normal charge rate,and heaters,lights etc were on, the lights dim and voltage drops. After the voltage has stabilised at 14-ish, no problem.

    As I had starting issues, I diagnosed a duff battery and got the worlds biggest tractor battery shoehorned in. This helped the starting, but no effect on the charging.

    I then decided it was the alternator, and changed it for a second hand unit. This appeared to improve things, but not by much.

    Today, MrsPaulF called to say the charging light was on, with the voltage gauge at 12v after stopping to fill up. Whilst talking to her (helping her to reduce the load) the light went out and the voltage jumped up to 14v. After about 15 minutes of driving, it went down again and stayed there.

    It seems to me as if there is a Generator Control Unit playing up, but as the car doesn't have one, I'm a little stuck.
    Is there a relay that the alternator charges through? (I'm thinking if so, it could be sticking) The other is earth straps - I did try jump leads from the engine to the negative terminal a while back, just in case the engine earth was playing up - no joy.

    Any thoughts would be welcome.

    I'm also having trouble with my wiring diagrams, so can anybody with a charging circuit diagram post it for me please?
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