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Thread: Voltage drop at higher RPM?

  1. #1
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    Default Voltage drop at higher RPM?

    Borrowing a truck to tow a trailer for moving.

    I noticed that when going up a hill and the engine kicks down (RPMs go up above 2800) the voltage will drop and the battery light goes on. It is otherwise is fine. Cruising around town it stays at 14 volts.

    2001 GMC Sierra 1500 5.3

    Searching the googles, people say its the alternator, the PCM, the voltage regulator and any other thing. Some say replacing the alternator doesn’t work cause the voltage regulation is outside the alternator.

    Then I read this article on RVC https://www.motor.com/magazinepdfs/042010_09.pdf. Which makes it more complicated.

    Any ideas?

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    If it was newer I would have suggested that maybe the alternator automatically disconnects to give more power to the engine under load?

    My bmw used to do that when you were pushing it, but that seems unlikely on a 2001 GM.

    Does the truck have airbags? Maybe the compressor is running overtime due to a leak when you tilt the truck up?
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    Had a 2008 4.8L do this at work, it was a bad regulator.

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    Regulator going or possibly the shift solenoid pulling way too much power. But that's probably unlikely, as you'd think it would be fused.

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    .
    Last edited by 01RedDX; 09-23-2020 at 04:25 PM.

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    Yea its the regulator/rectifier (cant recall which) thats typically internal to the alternator - but if its outside in your case, then start by replacing that. It functions as a heat sink to dissipate excess current and if its not working correctly, this can be the end result. Had this happen on a bike before.

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    Cool, thanks guys.

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