GMC Envoy lights dim when taking foot of gas

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Tom1234
Posts: 2
Joined: Wed Dec 12, 2012 11:16 am

GMC Envoy lights dim when taking foot of gas

Unread post by Tom1234 » Wed Dec 12, 2012 11:25 am

I have a GMC Envoy 4.2L 6cyl 2004 . at 1400 rpm I can see a flicker to all my lights including at the battery. Hi, I'm going around in circles with this problem. I've had two rebuilt alternators put on not solving the problem.

I also having dimming lights every time it does it(doesn't do it all the time about 6 times in 8 miles won't do it at high way speeds 60mph ish. ) I have just let go of the gas pedal (around 35mph) it will last about 2 seconds. grounds have been checked and including the red wire from alternator to battery. when the lights do dim the voltage at the battery went from 14.5ish to 12.8 almost like the alternator is not in the circuit.. any ideas would be great!

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ProTech
Posts: 651
Joined: Wed Oct 17, 2012 10:08 am

Re: GMC Envoy lights dim when taking foot of gas

Unread post by ProTech » Thu Dec 13, 2012 11:28 pm

I do have an answer for you on this, but you probably won't like it. This is an absolutely normal condition for your vehicle. You will not be able to fix it by changing alternators, putting in a new battery, cleaning and checking grounds, etc.

There is in fact a service bulletin from GM describing this problem to a tee, and then explaining that it is normal. While you may not like the lights flickering, or dimming, or the volt gauge going down, there is nothing you can do about it.

Now, for the technical stuff...your alternator has what is called a 'fuel saver' mode in which it will not charge, or charge very little, depending on the driving condition or battery state of charge. This explains when the gauge only reads battery voltage and not charging voltage. Different loads on the vehicle will draw down the system as well, which is completely normal. This can be having the A/C or defroster on, using the headlights, wipers, blower motor, etc...you get the idea.

The good news is, you don't have to spend any more money trying to fix it!
GM Dealer Technician For 18+ Years
In the automotive industry for 20+

Tom1234
Posts: 2
Joined: Wed Dec 12, 2012 11:16 am

Re: GMC Envoy lights dim when taking foot of gas

Unread post by Tom1234 » Sat Dec 15, 2012 10:38 am

thank you for your reply.. yesterday I had the garage put a brand new alternator instead of a rebuilt. reason the rebuilt had a sound of a bad bearing.. and it still dims and has a flicker.. I bought this suv new.. had the problem when I first got it not to this degree.. with your response that the computer is putting the alternator into a fuel saving mode.. I'm guess with a new battery I put a few months back probably this battery is getting to full charge faster then the old/dying one.. is there anyway of turning off this fuel saving mode???

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ProTech
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Joined: Wed Oct 17, 2012 10:08 am

Re: GMC Envoy lights dim when taking foot of gas

Unread post by ProTech » Sun Dec 16, 2012 9:26 pm

There is no way to adjust the computer's control of the alternator, either with programming or otherwise. This is just the type of thing that a person has to deal with, unfortunately, even if it is bothersome. It should put you at ease, though, to know there are no problems with the Envoy.
GM Dealer Technician For 18+ Years
In the automotive industry for 20+

dildargee1
Posts: 1
Joined: Tue Jan 20, 2015 7:17 am

Re: GMC Envoy lights dim when taking foot of gas

Unread post by dildargee1 » Tue Jan 20, 2015 7:24 am

This one is hard to see. You need to go through the wheel well or get under the truck. It bolts to the side of the engine block on a small bracket. It has one electrical connector and 2 vacuum lines.

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