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Thread: Car died (for a day). P2140? Or alternator/battery?

  1. #1
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    Car died (for a day). P2140? Or alternator/battery?

    So I was in stop/go traffic the other day, first the P2140 shuts my carPC off, then my power windows stop working and along with my other electronics. Then the battery light came on and my car almost died. I immediately pulled over and unplugged the computer's AC cord thinking that might help the car stay running. I've had this same thing happen when my alternator died a year or two ago (before I had the carPC), so normally it would be an easy diagnosis for me, but here's why I'm confused.
    I barely got my car home, parked it thinking it would be completely dead in the morning. But it started right back up without a problem. I've been driving it for the past few days (still with the carPC unplugged) without a problem. I plugged it back in today (worried that the extra drain would kill it again) and drove it throughout the day, but again without a problem.
    At first I thought the P2140 died, and the computer ate my battery, which is why my car died. But now I'm pretty sure the P2140 is fine since everything carPC related is working fine.
    I guess I just need a second opinion before I take the Lexus into a shop and spend money on a new alternator or battery. Anyone have any thoughts what would have happened?

    LOL did a solar flare interfere with my cars electronics or something!?
    - scENFORCER

  2. #2
    FLAC SNOtwistR's Avatar
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    I would say its the alternator, your car started the next day as your battery had a chance to build itself back up to its normal level. a good battery will do that. You having unplugged your stuff made the draw very little during the day as you would have no lights on. just my 2 cents SNO

  3. #3
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    An intermittent that lost the alternator. Intermittent could be any thing from the dash (charge light, IGN +12V) to the alternator itself.

    [Hence why I like dash voltmeters, else under-voltage alarms.]

  4. #4
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    Talking

    As this post relates to batteries, I thought this would be a good place to post it. This has occurred to you personally: You've left the car headlights on overnight, and now your automobile's engine won't even turn. Yet one hour later, it lives. What is happening with that hefty 12-volt lead-acid automobile battery? I found this here: Why batteries go dead and other tales.

  5. #5
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    Not applicable - read the original post.

    The self-recovery was covered in the replies.

  6. #6
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    Well, since the first time my car almost died the problem has gotten worse. When sitting in traffic (idling at low rpm's) the battery light has come on and the car almost died. CarPC shut itself off, windows and lights died, etc (typical dead alternator symptoms). I kept it running my keeping the rpm's up, however the car eventually completely died on me. Today I had a mechanic look at it, and he says the alternator is fine. He said the carPC is somehow draining the battery. He's going to recharge the battery and told me to run without the carPC for a few days.
    I dont think its the carPC. I dont understand why it would work fine for 7-8 months, then all of the sudden decide to drain my battery? I am having a slight ground problem (static through the speakers while amp car is on and carPC is off), but I dont think that's the problem either.

    Anyone have any suggestions for me? I still think its the alternator despite what the mechanic says..
    - scENFORCER

  7. #7
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    Me too, but it could be a bad battery dragging down the alternator.

    Voltmeter, voltmeter or voltmeter.
    Then see if the alternator charges above 13.8V to 14.4V - except perhaps at idle with "heavy" loads.

    See if the battery is up to 13.7V once charging ceases - which should drop to ~12.7V open circuit (overnight).
    etc etc.

    Otherwise lights on and see how much the brighten or dim with RPM... (Shouldn't work for HIDs though....)

  8. #8
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    Well my mechanic checked both the alternator and battery a few days ago with a voltmeter, and said they alternator was fine. The battery was completely dead. So he charged my battery for me and I've been driving the car without any problems for the past few days, albeit with my carPC unplugged.
    After speaking with a guy at a battery shop, he said that car audio systems really drain the battery down, especially if I have it running without the car on (which I have been doing to tweak with settings in Windows). He also mentioned that the ground issue I'm having can cause problems for my cars electrical system as well. He said if the ground is really bad, the alternator can get confused and not know whether its charging or not.

    Last night I tried plugging the carPC back in. I started up the car, and nothing. Computer didnt boot up, and the screen didnt turn on. I'm guessing I blew a fuse at some point during this whole ordeal? Any insight on this? I hope my P2140 isin't fried..

    So anyways, I just called my car audio guy, he said he can fix the grounding problem easy. Once they do that they'll look into diagnosing why my carPC is dead. He also said that the static coming through my speakers (while the car is on, and the carPC is off) is not a result of a bad ground. He said it's probably being caused by some other disturbance.
    Should I be worried about this static (it goes up and down with my rpm's)? He said he'd look into it as well, but does anyone have any guesses on where to look?
    - scENFORCER

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