2000 Chevrolet Silverado Alternator Cutting In And Out

SUDSMAN1

MEMBER
2000 CHEVROLET SILVERADO
5.3L
V8
2WD
AUTOMATIC
112,000 MILES

In the morning when I first start the truck the voltage output is fine at about 14.2 volts. After I have used the truck for a while, park and turn the engine off, I'll come back and start up again and the voltage shows around 11 volts. It will stay that way for a while until something shifts or wiggles somewhere in the engine, at which point the voltage will then climb up to the normal 14.2 volts. The voltage to the small wire in the plug on top of the alternator reads 1.27 volts (don't know if this is the field wire) while the output is low. Any idea what the voltage should be on the small wire and is that wire fed from the PCM, AND is there a name for that wire.

3 Replies

TY ANDERSON

MECHANIC
684 POSTS

According to my resources there are two small wires. The brown wire is the charge indicator signal. The grey wire is the charge duty cycle controller circuit.
Some alternator will begin to fail with heat, as the alternator warms up parts inside the alternator will expand in side and loose good contact within the circuits and when it cools down the contact improves.
Check the large red cable electrical connections at the alternator and the battery terminal clamps are tight and not corroded. Make sure the belt tension is tight and not really loose. The belt is tensioned automatically by the tensioner pulley so it should be tight enough.
When the vehicle shows it isn't charging, open the hood and tap the alternator with a mallet (do this with the engine running) or the wood handle of the mallet and if this corrects the charging voltage, plan on replacing the alternator assembly
Thanks for the question

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Tuesday, May 20th, 2014 AT 6:11 PM

SUDSMAN1

MEMBER
1 POST

Hi and thanks for getting back to me quickly. I did as you said (rapped hard on the alternator) and the voltage jumped up to the correct level. I took the alternator apart today and tightened all the screws and cleaned the brushes. There is only one small wire on the plug which now reads 12.6 volts and there does not seem to be a regulator built onto the altenator. Is there a regulator located somewhere else or does the PCM do the regulating? This is one of the towing package alts with higher amperage.

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Wednesday, May 21st, 2014 AT 6:45 PM

TY ANDERSON