Battery gauge fluxuation???

hi all:
I have been noticing a possible voltage issue in my 2001 Yukon. When it idles or when I slow down to stop I notice that my voltage goes down to around 10volts then goes back to 14/15 volts. I have a new battery, belts, tensioner, and had the alternater checked and it is fine. What gives? I also have subs and an amp with a 1farad cap. I still notice when the bass hits the lights still dim. Could it be a bad cap? Any ideas would be appreciated. Thanks.

Unlike the older generators, alternators will provide some power even at low speed. However below around 1000 RPM engine speed their output drops off, and with your power hungry electronics you might not be making enough power at idle, which means that the battery has to make up the difference.
Your comment about the voltage sagging to 10V leads me to think that you may indeed have an alternator on the way out. A fully charged battery should be about 12.6 volts, when it drops to 10 volts it's either undercharged or under extreme load.
Try the following:
Turn off all of your electronic accessories, then start the engine and keep the RPM at 2000 for a minute or so. Then let the engine return to idle and check the voltage, it should be above 13V with no load.
Check the capacity of your alternator, generally Yukon's come with pretty heafty alternators, but you might need to install one with a higher capacity.
Another possibility is that one of the diodes in the alternator has gone bad. If it wasn't checked at full load it could produce power at speed but not as much as it is rated for, and at idle its output would sag.
It could also be a bad connection at the alternator which drops voltage as the output increases.
A good automotive electrical shop can tell you what your problem is, and perhaps it's worth the $$ to find out before you take out your new battery.

Good luck, let us know what you find
94

I had the same problem with my 02 Yukon Denali, and it got progressively worse to where it begin to turn off as a came to stops and turned in to parking lots/ spots. So I took it in to the dealer and they said it was the throttle body I got back today and the battey gauge fluxuation went away. Maybe you have the same issue.

erlthesqrl:
What was the problem with the throttle body and how did they fix it? I replaced the alternator with a new 140amp and I am still seeing the fluxuation. Thanks.

Well, I didn't really ask what was wrong with it. They just told me that the battery fluxuation and my yukon cutting off when I'd make a turn in parking lots or stops at lights etc. was the throttle body going bad so they replaced it. I will ask them in the next few days and let you know what they exactly did, being that Im waiting on a driver sideview mirror because mine broke (defective mirrors/bad design in the folding mechanism).

Thanks erlthesqrl:
I am going to clean mine out and see if that helps at all.

Thanks erlthesqrl:
I am going to clean mine out and see if that helps at all.

What type of results did you get with cleaning your TB? I have replaced the battery, alternator, and put an overdrive pulley in and still have problems. Also, how did you go about cleaning the TB? Thanks.

Have you checked the voltage with a digital volt meter. You can't always trust the gauge. I figure all the dealership would do is turn up the idle about 100 RPM's. Those damn things idle at 500 RPM's in neutral, anyway. A little slow if you ask me..

Have you checked the voltage with a digital volt meter. You can't always trust the gauge. I figure all the dealership would do is turn up the idle about 100 RPM's. Those damn things idle at 500 RPM's in neutral, anyway. A little slow if you ask me..

I have checked the voltage and it does drop to the 12v mark and then back up to the 14.5v. The alt is new and both batt/alt tested fine. How can you turn up the idle? I thought they idled a little low myself. Thanks.

Most have a throttle stop screw located on the throttle body. If it's not hidden behind a plug.. They're usually torx.