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Virtual Wrench
Virtual Wrench, Master Mechanic
Category: Car
Satisfied Customers: 14620
Experience:  35 years/Master Tech. Foreign and Domestic
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2004 Yukon: wheel drive..000 miles..the alternator and battery..rpm

Customer Question

I have a 2004 Yukon XL 1/2 tonXXXXXwith 50,000 miles. I had to have the alternator and battery replaced in April 2008. A couple months ago I started getting voltage drops anytime the rpm reached 2,500 to 3,000. Going up a steep incline the voltage drops under 12 volts, and continues to pulse up and down until the vehicle shifts back into 4th gear. The lights dim, so I know the gauge is accurate. I am not sure if a diode went bad, and it only shows when more output is required.    Do you have any suggestions?
Submitted: 9 years ago.
Category: Car
Expert:  Carhelp4u replied 9 years ago.
Do you get a charge indicator light at these times? Do you ever get a check engine light at this point? What brand alternator are you using?
Customer: replied 9 years ago.
No indicator lights came on. I only noticed it because of the dash and head lights dimming. Then I saw the voltage gauge dropping. The voltage drop may not be long enough to trigger the indicator, as the voltage drops do not last long. I will back off the accellerator.
Expert:  Carhelp4u replied 9 years ago.

I hate to do it, but I am going to have to opt out. I am having a technical problem getting logged into my technical sites. I will get back to you asap if no one else has not. Sorry for the delay.

Expert:  Virtual Wrench replied 9 years ago.



Carhelp4uhere asked me to help out here.


I found a TSB on the alternator being mis-stamped with the wrong Amp's.


Do you know the amp output of the alternator thats in it?



Customer: replied 9 years ago.
105 amps
Expert:  Virtual Wrench replied 9 years ago.



It's supposed to be a 145 amp alternator. This is what might be giving you trouble, especially under a heavy load..

Customer: replied 9 years ago.

They had 2 different versions in 2004. The 105 and the 145. I have a basic package without onstar or navigation.


I had this serviced at the dealer in April, so I am assuming they installed the proper alternator and battery.

Expert:  Virtual Wrench replied 9 years ago.

I see,


I'm afraid the only thing that i can think of would be that it blew a diode and causing this. I recommend having the dealer check it, it might still be under warranty. Dont worry about the except if you dont want to because i sure cant tell you without a doubt where the fault lies without being there to test.


Best of luck my friend!