Alternator going bad or what? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Willie 66 · 10-28-2016, 11:31 PM

Hey all,

Got an '02 Sierra 1500. With a warm engine sitting at idle around 500 rpm and exterior lights on (nighttime), my interior lights on the dash flicker a bit. I have just over 14V, but if I put any amount of additional load on the electrical system (blinker or power windows), it *really* becomes noticeable and I can see the needle on the voltmeter dip down to 14V or less. Even in daytime, I notice the gear display light and the "message center" LCD screen flicker a bit. Problem goes away at anything above idle.

Just wondering if this could be indicative of something starting to fail. No troubles starting the truck. Just replaced plugs and wires last weekend. Changing belts tomorrow. Could it be the belt slipping on alternator pulley? The belt squeals a bit on cool mornings, but never the afternoon. Or is this a symptom of an emerging alternator/battery issue?

69chevytrucker · 10-29-2016, 12:13 AM

if you have a/c check idler bearing that is most likely why your belt is squealing.
common problem with that gen of truck i used to have to change the idler bearing every year or 2 .
as for the dimming if you have the full sweep type dash ( gauges sweep on start up ) then your cluster is probably dying mine had the speedo slowly stop working and the gear light was almost invisible . the oil pressure gauge would sit all the way to the right . gm knew of the issue with the sweep cluster and then they stop making them sweep for a few years.

Willie 66 · 10-29-2016, 06:32 PM

Well, I already bought new belts haha. The current belts are old and cracked anyway. But if that doesn't fix the squeal, then I know what the problem is!

Back to the original question: I don't have full-sweep gauges. All gauges and backlights work as normal, no sticking and everything comes up to temp, pressure, etc. except for the problem with the voltmeter and lights I described above. Even happens when I hit the brakes! Again, only at idle.

69chevytrucker · 10-29-2016, 06:36 PM

start your truck and then disconnect the battery see if it still runs if not then the alt is shot

**truckdude239** · 10-30-2016, 10:41 AM

Quote:

Originally Posted by 69chevytrucker

start your truck and then disconnect the battery see if it still runs if not then the alt is shot

DO NOT DO THIS it can and will fry the computer on new trucks the battery helps to stabilze the voltage if you unhook the battery while running you can cause a voltage spike that will fry the computer

Willie 66 · 11-03-2016, 01:05 PM

Update: Replaced the belts (they most definitely needed to be replaced), squeal went away but the electrical problems remain the same. Guess that rules out the belt slipping on the alternator pulley. That was just a wild guess anyway. Everything still works fine - just wondered if there was some PM I needed to do.

I guess I'll just wait til something breaks.

10-28-2016, 11:31 PM	#1
Willie 66 Registered User Join Date: Mar 2014 Location: Houston, TX Posts: 44	Alternator going bad or what? Hey all, Got an '02 Sierra 1500. With a warm engine sitting at idle around 500 rpm and exterior lights on (nighttime), my interior lights on the dash flicker a bit. I have just over 14V, but if I put any amount of additional load on the electrical system (blinker or power windows), it really becomes noticeable and I can see the needle on the voltmeter dip down to 14V or less. Even in daytime, I notice the gear display light and the "message center" LCD screen flicker a bit. Problem goes away at anything above idle. Just wondering if this could be indicative of something starting to fail. No troubles starting the truck. Just replaced plugs and wires last weekend. Changing belts tomorrow. Could it be the belt slipping on alternator pulley? The belt squeals a bit on cool mornings, but never the afternoon. Or is this a symptom of an emerging alternator/battery issue?

10-29-2016, 12:13 AM	#2
69chevytrucker Registered User Join Date: Apr 2014 Location: calgary alberta Posts: 1,248	Re: Alternator going bad or what? if you have a/c check idler bearing that is most likely why your belt is squealing. common problem with that gen of truck i used to have to change the idler bearing every year or 2 . as for the dimming if you have the full sweep type dash ( gauges sweep on start up ) then your cluster is probably dying mine had the speedo slowly stop working and the gear light was almost invisible . the oil pressure gauge would sit all the way to the right . gm knew of the issue with the sweep cluster and then they stop making them sweep for a few years.

10-29-2016, 06:32 PM	#3
Willie 66 Registered User Join Date: Mar 2014 Location: Houston, TX Posts: 44	Re: Alternator going bad or what? Well, I already bought new belts haha. The current belts are old and cracked anyway. But if that doesn't fix the squeal, then I know what the problem is! Back to the original question: I don't have full-sweep gauges. All gauges and backlights work as normal, no sticking and everything comes up to temp, pressure, etc. except for the problem with the voltmeter and lights I described above. Even happens when I hit the brakes! Again, only at idle.

10-29-2016, 06:36 PM	#4
69chevytrucker Registered User Join Date: Apr 2014 Location: calgary alberta Posts: 1,248	Re: Alternator going bad or what? start your truck and then disconnect the battery see if it still runs if not then the alt is shot

11-03-2016, 01:05 PM	#6
Willie 66 Registered User Join Date: Mar 2014 Location: Houston, TX Posts: 44	Re: Alternator going bad or what? Update: Replaced the belts (they most definitely needed to be replaced), squeal went away but the electrical problems remain the same. Guess that rules out the belt slipping on the alternator pulley. That was just a wild guess anyway. Everything still works fine - just wondered if there was some PM I needed to do. I guess I'll just wait til something breaks.



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