Voltage drops when idling

[Rivieraracing]

What is the voltage when you are driving?

When idling, what accessories do you have on and running (headlights, stereo system, etc.) other than normal stuff?

Also, there are a few different amperage of alternators that can go on our trucks depending the level of trim and such, do you know what yours is or do you see any markings anywhere on the casing of the alternator? If a smaller amperage alternator, might do you some good to go to a different pulley for the alternator to allow it to spin a bit faster.

 

[ccapehartusarmyINF.(ret)]

there is only two alternators available a 105 amp and a 130 amp in the 2000 to 2006 tahoe yuk like a base model tahoe like mine 2002 ls 2wd came with a 105 amp originally
ifyou have a fully loaded LT tahoe or denali you most likely got 130 amp

 

[wreedps]

My tahoe has a brand new 160amp AC Delco alternator. It will sit at like that when I am driving also. Then randomly it will go straight up and down at 14v. I just check my battery voltage this morning and it was 12.2v. Then the alternator kicked in and sat at 14v as long as I was standing there. Once the engine gets up to full temp is when the needle drops like the picture I posted and it will stay there for most of the day.

I do not have any aftermarket electrical accessories. I am only running the AC. Standard headlights, etc...

---------- Post added at 05:41 PM ---------- Previous post was at 05:32 PM ----------

Well I just went a looked at my battery cables and I could move the positive cable real easy. I snugged the bolt down and now I cannot move it.

Yall think it is that simple?

 

[YukonXL04]

Yours has electric fans, which is why it waits until the engine gets hot for your voltage to drop. Also what model and brand alternator did you get? It may make more amps at 2000rpm over a stock 130, but what does it put out at idle is my question. Okay so warm the engine up with the AC on and check the voltage at the battery now that the connection is tight

 

[wreedps]

Yours has electric fans, which is why it waits until the engine gets hot for your voltage to drop. Also what model and brand alternator did you get? It may make more amps at 2000rpm over a stock 130, but what does it put out at idle is my question. Okay so warm the engine up with the AC on and check the voltage at the battery now that the connection is tight

Yes it does have efans!

Also I only buy quality parts for my vehicles. The brand alternator I bought was genuine AC Delco alternator from the dealer.

 

[wreedps]

Well tightening the positive battery cable did not fix it. It seems like a poster said above it is when the e-fans kick on its drops.

My question is do the e-fans ever turn off? I live in Houston so it is hot and I sit in lots of traffic. Even when I went 70MPH for several miles the e-fans never turned off.

 

[wreedps]

Well I was wrong about it being the efans. I just pulled in my garage and the gauge is low like the above pic. Efans not even running and meter says I am putting out 13V.

The more I think about it I have never heard the efans run. Could there be something wrong with them causing the problem?

 

[wreedps]

This sounds like my issue. And it sounds like its not a issue at all.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may comment that their volt gauge is fluctuating between 12 and 14 volts on their full size pickup / utilityvehicle (http://www.tahoeforum.com/showthread.php?t=2706#). Starting with the 2005 model year, light duty full size pickups and utilities, are equipped with a new Regulated Voltage Control (RVC) system. This system reduces the targeted output voltage to 12.6-13.1 volts when in "FuelEconomy (http://www.tahoeforum.com/showthread.php?t=2706#) Mode" to improve fuel economy. The alternator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted. See picture below for the normal operating range of the voltage gauge. Review PIT4426 if having concerns with keeping a camper/trailer battery properly charged.





Recommendation/Instructions:
No repairs should be attempted and please reference the owners manual under Section 3 (Instrument Panel) "Voltmeter Gage" for more information.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
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[YukonXL04]

Hmm... There ya go.

 

[wreedps]

Yep surprised no one on here heard of that for the 05s!
it says turning on tow/haul disables the system. I will test on my way home.