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Charging issue

Tiny
DIVIDES
  • MEMBER
  • 2005 AUDI A4
  • 4 CYL
  • TURBO
  • AUTOMATIC
  • 127,000 MILES
Battery light would come on sometimes but only after car has been driven for a while, and then if you turn it off and back on it would need jump. Replaced alternator and the volts at battery are 13-13.40 while idling and as soon as I hit the pedal to rev it up it drops to under 12. At the alternator the output is 14.47.
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Thursday, May 20th, 2021 AT 2:27 PM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
So the voltage at the battery is 14.47 when running? if so the battery might be bad. To be sure lets run down this guide to confirm the issue:

https://www.2carpros.com/articles/car-battery-load-test

Let us know what happens and please upload pictures or videos of the problem.
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Friday, May 21st, 2021 AT 10:54 AM
Tiny
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The voltage at alternator is 14.4 at the battery its 13.5, but when I hit the gas pedal while parked it drops to 11.90-12.90 then when I let off it goes back to 13.4 gradually.
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Friday, May 21st, 2021 AT 11:18 AM
Tiny
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And while parked if I turn the A/C on after its warm it goes from 12.20 fluctuates like crazy until it reaches 13.3.
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Friday, May 21st, 2021 AT 11:22 AM
Tiny
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Battery replaced twice with new ones.
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Friday, May 21st, 2021 AT 11:25 AM
Tiny
KEN L
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  • 48,363 POSTS
Did it do this with the old alternator too?
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Friday, May 21st, 2021 AT 11:37 AM
Tiny
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Yes.
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Friday, May 21st, 2021 AT 11:41 AM
Tiny
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Now says 13.8 but A/C hot, the ambient temperature reading -38. Where is the sensor for that?
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Friday, May 21st, 2021 AT 2:32 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
The alternator output is controlled by the PCM but lets check the connections to the alternator to confirm the PCM is going bad. This guide can help I have included the alternator wiring diagrams below so you can see how the system works:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what happens.

we need to keep this thread on the charging issue. Please post your new question here, you must be logged in.

https://www.2carpros.com/questions/new

Cheers, Ken
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Sunday, May 23rd, 2021 AT 10:13 AM
Tiny
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Never mind I sold it.
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Sunday, May 23rd, 2021 AT 10:46 AM

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