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Registered
2007 chevy
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30 Posts
Discussion Starter #1
I have a passport 9800ix, or whatever radar dectector thats hard wired. Sometimes after I get on it, (gas pedal), and go back to a cruise, the radar will say, "Low voltage, powering down." And it shuts off....I look at my aeroforce gauge and it shows 12.3-7 volts. Not 14.6 like it usually does. I turn my car off, usually while driving or at a light and start it back up, and everything goes back to normal. It doesnt always do it when i get on it. its done it when im cruising on the interstate.

I have replaced my alternator thinking it was the voltage regulator going out, but that didnt fix the problem, and I have a yellow top battery...The battery is good..i think, ive never had a problem with it cranking or anything so who knows. any ideas?

Thanks
 

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Registered
2007 chevy
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49 Posts
I've been told that are ecm s control the alternator and when it doesn't think the car needs 14 volts it turns the alternator off.
 

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Banned
2004 gmc
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26,181 Posts
The low voltage has been seen before sometimes as a SAIS system turbine air pump diagnostic, if it happens three times, three seconds between dips, about 5-15 minutes after starting off, but then driving at a steady speed. Other voltage dips are assumed (but we can't confirm) to be alternator/battery diagnostics where the PCM turns off the alternator for a short time, and watches the battery try to supply the vehicle by itself for a few seconds.

Personally, I think the PCM is way too curious, and the diagnostics alarm drivers more than they should be. Only way to be sure is to be monitoring the alternator suppression wire while things like this happen, to see if the PCM is commanding it, or if the alternator is drooping on its own volition.
 

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2002 gmc envoy_slt
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3,203 Posts
I'd almost be willing to go on a limb and bet you that one of the diodes in the diode pack sticks after the high-rpm exercise and results in lack of output from the alternator. Seen this before on alternators with internal voltage regulation. This usually happens on cold start in fairly cold weather, but the diodes are usually just a bit lazy form the cold until they have a few moments warm/wake up.
 

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Banned
2004 gmc
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26,181 Posts
Perhaps a problem in the diode package contacts to the socket they're installed in, but diodes are inherently solid state with no moving parts, no appreciable warm-up more than about 50mV change in voltage drop, and so forth. And the solid state voltage regulator is the same. Not like the old mechanical relay contact controlling the field current style of voltage regulator.

 
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