Results 1 to 14 of 14

Thread: Battery light on dash

  1. #1
    Join Date
    Dec 2008
    Location
    Scottsdale Arizona
    Posts
    343
    My Cars
    540iT 840Ci 850Ci 540i

    Battery light on dash

    .....so I'm driving my 2003 E39 540iT wagon down the road, and suddenly the battery light comes on, on the dash. I thought that the alternator stopped charging or the belt was off...... Wrong, the alternator is still sending 13.6 out to the battery, and obviously the belt is not off because the power steering still acts normal.
    Any ideas, any suggestions?

  2. #2
    Join Date
    Oct 2017
    Location
    Beaverton, Oregon, USA
    Posts
    1,694
    My Cars
    2001 E39 540i A, 207 k
    The alternator is about to check out...Replace it asap.

  3. #3
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
    Join Date
    Oct 2006
    Location
    Sundance Mesa, NM
    Posts
    19,817
    My Cars
    00 540/6, '16 Highlander
    Make sure the little connector that plugs into the top front of the alternator is clean and plugged in good.
    There is a small fuse (5A??) in that circuit too, make sure it's good. It's above the glove box.

  4. #4
    Join Date
    Dec 2008
    Location
    Scottsdale Arizona
    Posts
    343
    My Cars
    540iT 840Ci 850Ci 540i
    The plug at the top of the alternator was tight, but I took it out and cleaned it well, but that didn't fix the problem; the red battery light is still on, on the instrument cluster.
    #4 fuse was blown, but that wasn't the fix either.
    The battery keeps a good charge from day to day, and when the motor is running, the voltage is 13.5 to 13.7 which tells me the alternator is putting out properly.?
    ....anyone else have any ideas?

  5. #5
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
    Join Date
    Oct 2006
    Location
    Sundance Mesa, NM
    Posts
    19,817
    My Cars
    00 540/6, '16 Highlander
    F4 is for the general module. Any idea why it blew?
    The alt fuses I was thinking about was F15 & F18, check them. Maybe F4 again too.

  6. #6
    Join Date
    Jan 2015
    Location
    Tempe, AZ
    Posts
    7,657
    My Cars
    1995 525i/5
    Maybe the voltage regulator is acting up... usually when the red light comes up I replace the alternator, it’s not worth the risk of being stranded.
    1995 525i 5-speed - Thread

  7. #7
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
    Join Date
    Oct 2006
    Location
    Sundance Mesa, NM
    Posts
    19,817
    My Cars
    00 540/6, '16 Highlander
    With the alt putting out 13.6 - 13.7 volts it shouldn't be the alternator.

  8. #8
    Join Date
    Oct 2017
    Location
    Beaverton, Oregon, USA
    Posts
    1,694
    My Cars
    2001 E39 540i A, 207 k
    It IS the alternator or regulator. Its output is intermittent, and most likey often below the 13.6v threshold -when the red battery light come on.

  9. #9
    Join Date
    Aug 2016
    Location
    Virginia,USA
    Posts
    3,144
    My Cars
    528i, 525iT, M5
    Take a volt meter and test your battery voltage at the battery terminals (AFTER you loosen them, clean them and re-tighten the posts),

    Voltage test are at in the key off position, idle, 1500 RPM, and 2500 RPM Hold speeds for 15-30 secs record any variations.

    Report back your findings

    Engine Off Voltage:______________
    IDLE Voltage: ___________
    1500 RPM Voltage _______
    2500 RPM Voltage _______

    Any digital voltmeter will do.

    Note: Loose wires, corroded connectors (These things are 15+ years old now) on both the ground side and the positive side will provide bad readings. Clean and put a wrench on all of them. Especially the ones under the hood. When in doubt use the test below:
    Volt Drop Test
    Attached Images Attached Images
    Last edited by StephenVA; 04-22-2019 at 11:56 AM.
    Current Garage Highlights
    2003 525iT TiSilver
    2002 M5 TiSilver
    1998 528i KASCHMIRBEIGE METALLIC (301) (Goldie)

    Former Garage Highlights
    2005 X5 4.8is
    2004 325iTs (2x)
    1973 Pantera L
    1971 Dodge Dart Swinger "Lite Package"
    1970 Dodge Challenger T/A 340 Six Pack Alpine White
    1970 Dodge Challenger T/A 340 Six Pack GoManGo Green
    1969 Road Runner 383
    1968 Barracuda Formula S 340 Sea Foam Green

  10. #10
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
    Join Date
    Oct 2006
    Location
    Sundance Mesa, NM
    Posts
    19,817
    My Cars
    00 540/6, '16 Highlander
    While your at it remove and clean both ends of the ground strap from the pass side engine mount bracket to the body.
    My 540 has never been driven in the snowy salty winter when I lived back in MA, but I still found considerable corrosion on the bolt that holds the ground strap to the engine bracket. It didn't cause me any issues, yours could be worse??

  11. #11
    Join Date
    Nov 2018
    Location
    La Habra, CA
    Posts
    1,117
    My Cars
    2002 525i
    Does the 540 use the same alternator as the 525? I replaced my voltage regulator and saved a ton of money compared to a new alternator.

  12. #12
    Join Date
    Jan 2015
    Location
    Tempe, AZ
    Posts
    7,657
    My Cars
    1995 525i/5
    Quote Originally Posted by E39 Newbie View Post
    Does the 540 use the same alternator as the 525? I replaced my voltage regulator and saved a ton of money compared to a new alternator.
    No it does not. The 540i alternator is water-cooled and sealed up pretty tight. You can still take it apart if you're careful though, and there is a voltage regulator in it but they're much harder to find since very few people rebuild the water-cooled alternators. Most rebuilds of those are done by Bosch.
    1995 525i 5-speed - Thread

  13. #13
    Join Date
    Oct 2017
    Location
    Beaverton, Oregon, USA
    Posts
    1,694
    My Cars
    2001 E39 540i A, 207 k
    FYI, according to an employee at Bosh, the lifetime of the water-cooled alternator on the E39 540i is about 16 years, give or take.
    So, yours may be due for a replacement.

  14. #14
    Join Date
    Dec 2008
    Location
    Scottsdale Arizona
    Posts
    343
    My Cars
    540iT 840Ci 850Ci 540i
    Wow, what a lot of good input. I'm away from home until next Monday, so I will do the tests then......thanks everyone.

Similar Threads

  1. Red Battery Light On Dash Appearing Intermittantly
    By shane82388 in forum 2006 - 2012 (E90, E91, E92, E93)
    Replies: 11
    Last Post: 12-21-2015, 12:53 AM
  2. Battery light on dash off
    By GRKOALA in forum 1976 - 1989 (E24)
    Replies: 5
    Last Post: 11-11-2014, 08:36 AM
  3. E39 530d (03) constant red alternator/battery light on dash
    By cluster in forum 1996 - 2003 (E39)
    Replies: 15
    Last Post: 02-26-2012, 06:04 PM
  4. Battery light on dash
    By e38guy in forum 1995 - 2001 (E38)
    Replies: 1
    Last Post: 09-21-2011, 10:07 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •