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Thread: Random warning lights come on and battery dies

  1. #1
    Join Date
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    Random warning lights come on and battery dies

    First post here so bear with me. I just bought my first BMW 2 months ago. It's a 2005 325ci 5 speed convertible. I absolutely love it... but it's been giving me some crazy issues already.
    Going down the road, at complete random, my ABS, TCS, DSC, and tire pressure lights all come on at the same time. Cruise stops working, music dims, and at this point, I cannot shut my car off or the car acts like a dead battery. (One time my freaking gauges froze!) I've had the battery and alternator tested MULTIPLE times and the results are... interesting. Battery shows good on all tests (with over 100 CCA more than the battery shows) and alternator has tested good and bad. I bought a brand new one and it still tests good and bad. Only code popping up is P0335 for Crankshaft Position Sensor Circuit.
    Earlier today, I stalled the car on a red light. It was downhill, pushed it to 20 mph and a clutch jump would NOT start it. 5 minutes later, battery has just enough juice to start. By the time I get home, battery acts normal. PLEASE tell me someone on here has SOME type of information that could be helpful. I absolutely love this car but this problem is pushing me over the edge

  2. #2
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  3. #3
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    It sounds like the car is experiencing a general electrical fault. How many miles on the car? Is the alternator original?

    The first thing I’d check is the cables at the battery. The connections between the cables and the battery’s posts need to be clean and tight.

    Next, google “BMW E46 hidden OBC functions.” Test #9 shows the voltage as seen by the engine computer (DME in BMWspeak). I recommend you keep that data showing at all times so you can see the voltage when the car starts having issues.

    Electrical power from the battery runs up the right side of the car. The red cable from the battery connects to a couple of other cables at the jumper post located under the red plastic cover. I recommend you disconnect the battery’s ground cable and then disassemble that jumper post to make sure the conducting surfaces are clean and tight.

    Another thing to check is the engine ground cable. It’s located under the right front “corner” of the engine. It’s a large brown (brown is always ground in a bimmer) cable that runs from the engine to the chassis. Again, the conducting surfaces of the connectors need to clean and tight.

    How old is the battery? While a battery tests “good” there can be issues with it. Also, do you have any history of the alternator? Be advised that BMW sourced alternators from Bosch of Germany (yay!) and Valeo of France ( ). They are not interchangeable. The only way to tell which alternator is in your car is to pull the air filter box and use a flashlight and a mirror to read the label at the back of the alternator. Hopefully it’s a Bosch. You can replace the voltage regulator in a Bosch alternator fairly easily and cheaply (~$50 from FCPEuro). Replacing the voltage regulator in a Valeo alternator is more expensive. Those French!

  4. #4
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    Car has 130k. I just replaced the alternator last week. It has a rounded port for the harness. I think it's Carquest's version of Bosch.

  5. #5
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    Good, it’s likely a remanufacted Bosch alternator. However, I question what company did the rebuild.
    You need to check the voltage as shown in the gauge cluster readout. The issue could be that the “new” alternator is crap.

  6. #6
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    If battery age is unknown or over 5yrs old just replace.
    New battery and alternator pair should make you a happy camper!

  7. #7
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    Had the battery tested 4 times, all tests indicated a good battery. After charging, battery shows 12.5V with the car off and 12 at idle. After driving for a few minutes, battery drops down to roughly 10V. Let it sit, and it goes back up. However, straight from the back of the alternator, it stays at 13.8-14.1. Is there a relay for the charging system or could this be a parasitic draw?

  8. #8
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    Check both the positive & negative battery cable for loose connections,
    Or remove them completely and test for resistance end to end.

  9. #9
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    I checked both cables, no loose connections. I was unable to pull the entire cable out, but I checked the voltage on both ends and the results were identical.

  10. #10
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    Theoretically, if I were to test the voltage at the back of the alternator with the engine NOT running, should it be the same as the voltage at the battery?

  11. #11
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    Voltage at battery terminals:
    Engine running approx. 13~14volts
    NOT running approx. 12.6~12.7volts

  12. #12
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    03 zhp, 97 e36m3, 04 zhp
    "P0335 for Crankshaft Position Sensor Circuit"...

  13. #13
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    2001 525it
    I would take it to a good bmw shop for diagnosis

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