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Thread: Voltage surging until warm on 545i. Anyone have this?

  1. #1
    Join Date
    Oct 2015
    Location
    Huntley, Il, USA
    Posts
    7
    My Cars
    2005 545i, 2008 Jeep SRT

    Voltage surging until warm on 545i. Anyone have this?

    2005 545i with 145,xxx miles. Bunch of issues fixed, but have recently come into an issue since it has been consistently cold, and I'm not sure if that is just a coincidence.

    When I start the car, the radio intermittently starting going out for a quick second, then coming back on. Interior lights seemed to dim at the same time. I got out my meter, started when cold and measured voltage on terminals. I watched the voltage surge from 11-ish to 14.5-ish durng these surges, almost like the alternator is not throwing power into the battery on these power dips obviously. After the car runs for a bit, it seems to go away (when warm) and run just fine. Once in a while when cold and this happens, you can feel the power fall off on these low voltage dips, and again, when it stops, it runs just fine. There are even now times where during these power dips, the Dynamic Stability Control goes out and throws a code. After it's warm, I can literally shut the car down, then restart, and all is fine for an hour long drive...no issues.

    Sounds like alternator or some switching regulator.

    Any ideas what I should be looking at?

  2. #2
    Join Date
    Sep 2008
    Location
    Atlanta GA
    Posts
    95
    My Cars
    530I
    Battery should be at 12.5 so if you are seeing 11v I would say it's time for a new one.

  3. #3
    Join Date
    Feb 2017
    Location
    Arizona
    Posts
    2
    My Cars
    2005 545i
    My 05 545i has this same issue. Exactly as Pitster subscribed. Battery is brand new.

    Intermittently throws a steering or stability code. If i shut the car off after it warms up, it doesn't happen again, it seems, until the next day.

    Headlights, interior lights, HUD, and radio all blink for less than a second. It reoccurs between a few seconds to a minute until it warms up. It has never reoccured when shut off after warming up and immediately restarting. It won't reset when cold.

    Does anyone know of the fix/cause for this?

  4. #4
    Join Date
    Jan 2016
    Location
    Ca
    Posts
    6,981
    My Cars
    2001 525it
    Have a shop chec the alternator for excessive ac,leakage,if that is to high you can have alsorts of problems. Also some rebuilt alternators will have to much ac leakage, some folks now are using alternators from the dealer only.

  5. #5
    Join Date
    Aug 2007
    Location
    Canada
    Posts
    385
    My Cars
    750 F01, 850i, LR3 HSE
    Your alternator is more than likely failing, this fluctuation is usually due to a failed rectifier causing AC voltage bias or a failed regulator/brushes in the alternator and worn slip ring. Has said before just get it checked, also scan the car you may find under/over voltage faults.

    Also check the integrity of the engine to chassis ground.

    Mark.


    Quote Originally Posted by Pitster View Post
    2005 545i with 145,xxx miles. Bunch of issues fixed, but have recently come into an issue since it has been consistently cold, and I'm not sure if that is just a coincidence.

    When I start the car, the radio intermittently starting going out for a quick second, then coming back on. Interior lights seemed to dim at the same time. I got out my meter, started when cold and measured voltage on terminals. I watched the voltage surge from 11-ish to 14.5-ish durng these surges, almost like the alternator is not throwing power into the battery on these power dips obviously. After the car runs for a bit, it seems to go away (when warm) and run just fine. Once in a while when cold and this happens, you can feel the power fall off on these low voltage dips, and again, when it stops, it runs just fine. There are even now times where during these power dips, the Dynamic Stability Control goes out and throws a code. After it's warm, I can literally shut the car down, then restart, and all is fine for an hour long drive...no issues.

    Sounds like alternator or some switching regulator.

    Any ideas what I should be looking at?

  6. #6
    Join Date
    Feb 2017
    Location
    Arizona
    Posts
    2
    My Cars
    2005 545i
    Yep. Replaced the alternator and all is well. Thanks for the posts. This car performs better than it has in months. It's amazing.

    If you have this issue i highly recommend you immediately change your alternator. I didn't and it may have cost me huge. My car had a severe crash of several computer boards. I have to wonder if the glitching didn't cause these failures.

    It's not an easy part to replace, but i do recommend you do it yourself. I replaced mine for about $300 and some sweat.

    If you need more information on how to test your alternator, either get ahold of a Bentley manual or hit me up for more info. You'll need an o'scope. Hour this helps.

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