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Thread: Protege5 Alternator Overcharging

  1. #1
    Registered Member detroitcity's Avatar

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    Protege5 Alternator Overcharging

    I just replaced the battery and alternator in my 02 pro5.

    The battery light did not go out, so I took it to AutoZone where a bat/alternator test revealed that my alternator was overcharging (it's putting out somewhere in the neighborhood of 17 volts).

    This is what I am wondering:

    1. Is the alternator's overcharging symptomatic of a larger system problem; ie: PCM/ ECU problems?

    2. or is it possible that I just got another bad alternator.

    I purchased this car yesterday and I noticed that the battery had much corrosion on the positive terminal. (the fact that the old battery was seemingly overcharged leads me to believe that the previous battery/ alternator combination had the same problems)


    How would you track down a problem like this?

  2. #2
    Resident Asshole Maxx Mazda's Avatar
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    What alternator did you get? One specific for the Protege? Cause the ones from older 626's etc will fit and look identical, but atre internally regulated, vs ecu regulated on the stock one. If you got one of those instead maybe the ECU isn't liking not having control over it. I know there's a tiny wire mod you have to do to get it to work right, but it's jsut a thought.


    Completely stock...

  3. #3
    Registered Member detroitcity's Avatar

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    Quote Originally Posted by Maxx Mazda View Post
    What alternator did you get? One specific for the Protege? Cause the ones from older 626's etc will fit and look identical, but atre internally regulated, vs ecu regulated on the stock one. If you got one of those instead maybe the ECU isn't liking not having control over it. I know there's a tiny wire mod you have to do to get it to work right, but it's jsut a thought.
    interesting... so you are suggesting I might try a 626 alternator and modify the wiring.

    What kind of mod?

  4. #4
    Resident Asshole Maxx Mazda's Avatar
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    No Im suggesting that they maybe put a 626 alt on by mistake, and it's trying to regulate itself while the ECU is too...
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  5. #5
    Registered Member Benji's Avatar

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    if your alternator is overcharging then it is most likely defective. although, if the p5 has an external regulators and it is true that you last alternator had the same problem then then there lies your problem.

    Also I could understand how the 626 alternator would confuse the ECU but why would it cause overcharging it is internally regulated so therefor it should put out 14.4 volts regardless
    Last edited by Benji; 05-08-2009 at 03:01 AM.

    engaging flux capacitor

  6. #6
    Registered Member detroitcity's Avatar

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    Brought the car to a dealer who replaced the defective alternator.
    Everything seems to be running well.

    I curse the hours I wasted yesterday installing a "new" defective alternator.

    I've read quite a bit about bad remanufactured alternators, I'll buy all of mine from the dealer from now on, to avoid the bitch of a job that is the alternator on this car.

  7. #7
    Registered Member Benji's Avatar

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    you might also want to think about changing where you buy your parts. buy oem parts online or use a parts store that shops use like auto parts international.
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  8. #8
    I hate spam. Rockin03mp5's Avatar
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    i had a very similar problem (f-u firestone!)

    brought it to the dealer and now is all better.

    my "new" alternator was overcharging, then undercharging. popped both my headlights in 1 day. since i got it fixed at the dealer... no more problems. now i have HID's though, but i was almost a year with regular bulbs.

    was your battery bad too? i know my battery went bad, but that was probably cause my alternator wasnt charging it right.
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    I have the same problem. !7V after Mechanic changed the alternator. Do you think it was a bad alternator?

    The old one had bad bearing and was causing drag on belt and was producing about 12.5V. But car was running with battery sign. Once I removed the negative terminal from battery, car died. So I conclude bad alternator (old).

    But once I replaced, the new one has over voltage problem!!!
    Any advice?

  10. #10
    Registered Member pasadena_commut's Avatar

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    Quote Originally Posted by surefire2007 View Post
    I have the same problem. 17V after Mechanic changed the alternator. Do you think it was a bad alternator?

    The old one had bad bearing and was causing drag on belt and was producing about 12.5V. But car was running with battery sign. Once I removed the negative terminal from battery, car died. So I conclude bad alternator (old).

    But once I replaced, the new one has over voltage problem!!!
    Any advice?
    The replacement alternator is bad, 17V is much too high. Take it back and make them fix it. This sort of thing is unfortunately fairly common with replacement alternators. If you drive it very long like that it will kill your battery and potentially other components.

  11. #11
    The Diagram Dude pcb's Avatar

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    One of my four alternators went to 17V then killed the battery over night. Jumped it the next day and it shot back up to 17V so I turned on everything electrical which brought the voltage down then I drove it to the shop.

    It was a bad alternator.

  12. #12
    Registered Member pasadena_commut's Avatar

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    Quote Originally Posted by pcb View Post
    Jumped it the next day and it shot back up to 17V so I turned on everything electrical which brought the voltage down then I drove it to the shop.
    That's a good point, heavily loading the alternator may bring it down to a voltage that will do less damage to the battery. But I wouldn't turn on the sound system, especially an expensive aftermarket one. Go with the headlights, the fan on position 4, and I guess the A/C on full cold. The compressor itself is belt driven but if the load causes the car to heat up then the fan on the radiator may come on, and neither the compressor clutch nor the radiator fan should be damaged by 17V. If you happen to have one of those compressors (for tire inflation) that plug into the cigarette lighter socket, that would be a good thing to run too. The power windows take a fair amount of current, I guess one could run them up and down on the drive over, but the other drivers would think you were insane.

    The thing that is most galling about this sort of situation is that the mechanics give the customer the car back without checking the output voltage, which invariably destroys the battery before the problem is discovered.

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