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  1. #1
    Established Member Two Rings
    Join Date
    Sep 17 2014
    AZ Member #
    283343
    Location
    Columbus, OH

    Alternator vs Battery vs Drain (car keeps dying)

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    So, my S4 recently started having electrical issues.

    When the issue first started, I noticed that when I turned off my car, the fan (main fan, not AC) kept running. This happened only once but of course I returned later to a dead car. Jumped it, drove home and everything was fine. Fan hasn't been turning on while car was off since that one time (which is odd).

    Car would start up fine right after turning off. After sitting for half a day I would return to a dead car. My battery is about 5 years old. At first, I thought the issue was my battery since it was old but I had O'Reillys check it and they said the battery was fine and the culprit is the alternator. I checked the belt and it looks okay, looked at it while car was running as well and its spinning smoothly. I drove home from O'Reilleys, turn off car, and it started back up the next day fine. Didn't drive it but after being parked for a day, it was completely dead.

    What led me to believe that something is draining the battery while the car is off was that it keeps dying after sitting for a while. And the fact that the fan kept running that one time is weird.
    Could it be the alternator is on its way out? Charging the battery on some drives? But that wouldnt make sense why the car dies after being parked for a while.

    Any ideas to trace a drain? O'reillys says battery is fine but could that be going out soon since it's been 5 years since I replaced?

  2. #2
    Senior Member Four Rings VinnysS4's Avatar
    Join Date
    Nov 12 2015
    AZ Member #
    364349
    Location
    Oregon

    The fans staying on after shut down is indicative of either a faulty fan control module, or water getting into the ecu box. I would start at the ecu box and check the seal. Male sure the relays aren't corroded. Then I would check the FCM. Both issues could deffinately drain the battery and have nothing to do with charging or battery condition.

    Sent from my SM-N920V using Tapatalk
    1997 VW GTI VR6 (sold), 2003 Audi RS6 (sold), 2010 Audi A4 2.0T (RIP Totaled on 11/2/2015 ) 2005.5 Audi S4

    My build log
    http://www.audizine.com/forum/showth...-s-s4-timeline

    Texpoops "Correct, but a half inch difference isnít going to accelerate wear by much. Iím sure the front dips that much with a fatty in the front"

  3. #3
    Established Member Two Rings
    Join Date
    Sep 17 2014
    AZ Member #
    283343
    Location
    Columbus, OH

    Quote Originally Posted by VinnysS4 View Post
    The fans staying on after shut down is indicative of either a faulty fan control module, or water getting into the ecu box. I would start at the ecu box and check the seal. Male sure the relays aren't corroded. Then I would check the FCM. Both issues could deffinately drain the battery and have nothing to do with charging or battery condition.

    Sent from my SM-N920V using Tapatalk
    I did leave my ecu box open over the summer while it rained, there was a tiny bit of water in there. I made sure to clean up the water and dry it before starting. But that was months ago. I just checked the box and took off any corrosion on the fuses.
    The fan stayed on only 1 time, it hasn't happened since.

    Jumped the car this morning, drove it around. Got it checked at Autozone this time. They said the battery was 100% but the alternator was bad. Test showed that diodes were good but regulator was bad?
    Could a bad alternator be draining the battery while the car is off as well?

    When I use a multimeter to check drain, how much drain is considered normal with all the security system, etc?

  4. #4
    Established Member Two Rings
    Join Date
    Jan 25 2018
    AZ Member #
    413002
    My Garage
    2004 Boxster S 550 SE
    Location
    St Catharines

    Funny you posted this Im actually going throught similar issues at the moment and just figured out my fault.

    Do you have a digital multimeter?
    2004 Boxster S SE, 2006 Audi A4 Avant 2.0 Quattro

  5. #5
    Established Member Two Rings
    Join Date
    Sep 17 2014
    AZ Member #
    283343
    Location
    Columbus, OH

    Quote Originally Posted by GTA_G20 View Post
    Funny you posted this Im actually going throught similar issues at the moment and just figured out my fault.

    Do you have a digital multimeter?
    Not yet, but I can get one today. How did you fix yours?

  6. #6
    Established Member Two Rings
    Join Date
    Jan 25 2018
    AZ Member #
    413002
    My Garage
    2004 Boxster S 550 SE
    Location
    St Catharines

    Bought a multimeter. Charged battery with the negative terminal disconnected from the battery.

    Open drivers door and latch the lock with flat head screw driver . Set meter to 10A. Normal drain should read 0.02A or 0.03A.
    Connect red lead to negative battery terminal and black lead. To negative battery cable car side. It should spark it's normal on initial connection. Your drain should be above what the normal is which mine was 2.47A. Open fuse box and remove fuses one by one. Until the amperes drop off

    Sent from my E2306 using Audizine mobile app
    2004 Boxster S SE, 2006 Audi A4 Avant 2.0 Quattro

  7. #7
    Registered Member One Ring
    Join Date
    Sep 22 2018
    AZ Member #
    427317
    Location
    Stuttgart Germany

    My battery was dying overnight due to the SAI. Faulty relay, was activating the SAI at night at full speed. Relays are really cheap but under the ECU so be careful not to crack the windshield...

  8. #8
    Established Member Two Rings
    Join Date
    Sep 17 2014
    AZ Member #
    283343
    Location
    Columbus, OH

    After cleaning the fuses, car is no longer dead in the morning! Thanks for the help fellas!



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