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Bad Battery or Bad Alternator?

Discussion in 'E46 (1999-2006)' started by EvaUnit02, May 18, 2011.

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    EvaUnit02

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    I have a 2001 330xi. I was driving back to the office from lunch and the red battery light came on along with the ABS light. The car kept running just fine but accessories started shutting down: radio, windows, mirrors, etc. Lights seemed on but I turned them off. Wipers worked but slowly. When I got back to the office, I parked, shut off the car, and tried to start it again. It wouldn't start. Position 1 would turn all of the accessories on like normal. Trying to start the car would reset everything: clock, radio, cabin thermostat settings, etc.

    The indicator on the battery itself says it's dead (the indicator is black). I'm going to replace the battery (it's four years old) and see what that does. Then, I'm going to hook up a voltmeter to see if the alternator is bad. I also had checked to make sure no belts snapped.

    Am I doing the right thing? Anything wrong or missing in my troubleshooting procedure? Does it sound like a bad battery or a bad alternator? Too soon to tell?
    • Member

    MGarrison

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    Your plan sounds good to me - hopefully it's just the battery.
    • Member

    RickQuinn

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    Battery/Alternator

    I had a similar experience with my 2002 325XiT. Replaced the battery only to find that it was in fact the alternator. The battery was 6+ years old and still serviceable. :)
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    • Member

    alvocado

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    This is likely your alternator. I had the same thing happen last week with the red battery warning light followed by the car dying. Your car will run on the battery alone until it's drained when the alternator dies.

    My alternator wasn't making any noise and the pulley would spin free with no sign of bearing failure. I took a chance and bought a replacement voltage regulator for $40 off AutohausAZ and it solved the issue. Apparently, it's not uncommon for the VR's to fail yet the alternator itself is still fine. You do have to pull the alternator to replace the VR but it was a very easy repair and took about an hour.
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    • Member

    EvaUnit02

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    Turned out to be the alternator after all. Ah well, my battery was pretty old. At least, that's how I'm justifying my gamble on the new battery!

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