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Have a charging issue. start engine, alternator is cranking

out 14.5 volts. within a...
have a charging issue. start engine, alternator is cranking out 14.5 volts. within a minute or two it starts to put out less and less volts until i am completely running on the battery in about 10 minutes
JA: Have you checked all the fuses? Do you have a wiring diagram?
Customer: ive taken the alternator in to be checked and it passed bench test and have tried 4 different alternators and a couple batteries
JA: What is the model of your '14 GMC?
Customer: its an 06 yukon xl denali
JA: Are you fixing your Yukon XL yourself? What have you tried so far?
Customer: i am replaced alternator and battery a few times checking volts at the alternator and comparing to volts across battery posts im not sure which fuse to check
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
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Answered in 11 minutes by:
9/13/2016
david craig
david craig, Owner/[email protected] 3D Atuomotive
Category: GMC
Satisfied Customers: 4,194
Experience: owner/mechanic at 3D Automotive
Verified

Hi Im David, allow me a few moments to look up some info for your vehicle. what size engine do you have?

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6.0 i imagine

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you have a bad generator battery control module.

1. Disconnect the engine harness electrical connector from the generator battery control module.
2. Remove the negative battery cable.
3. Cut the tie straps and electrical tape attaching the generator battery control module to the battery cable.
4. Squeeze the negative battery cable branches together.
5. Slide the generator battery control module off of the negative battery cable.

IMPORTANT: Note the orientation of the generator battery control module prior to removal.

INSTALLATION PROCEDURE

1. Slide the NEW generator battery control module up onto the negative battery cable.

IMPORTANT: Prior to installation, ensure that the orientation of the generator battery control module (once completely installed on the negative
battery cable) will be such that the module's connector will be closest to the battery's negative terminal as shown in the above graphic. The orientation
of the module on the negative battery cable is critical to the proper functionality of the module once installed in the vehicle.

2. Using NEW tie straps and electrical tape, attach the generator battery control module to the negative battery cable.
3. Install the negative battery cable.
4. Connect the engine harness electrical connector to the generator battery control module.
5. Program the generator battery control module. Refer to Generator Battery Control Module Programming and Setup

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Customer reply replied 1 year ago
Wow. I found some information on this module, and never knew this was a thing. I just purchased this a couple weeks ago and have been going crazy with it. Do you know where I can get a new module?
Customer reply replied 1 year ago
6.0L

let me see if i can find a source

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is that thing a hybrid?

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Customer reply replied 1 year ago
It is not a hybrid. Stock Yukon XL Denali with 6.0L engine. I also found a busted ride height sensor in front driver suspension that I disconnected this morning just in case it was causing grounding issues.Thanks for your help

still looking for a source other than the dealer

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Customer reply replied 1 year ago
ok. thanks. I'll be replacing the ride sensor tomorrow to take care of the service suspension system light now that i disconnected the busted sensor.

cant find a good source

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Customer reply replied 1 year ago
Neither can I. I will go to a dealer if it starts acting up. You helped me a lot with identifying a system I didn't know existed, and it proved that my issue was a non issue. I'm just not used to volts being below 13 off the alternator when the engine is running.

and it shouldnt be. anything below 14.4 is not good

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please accept the answer and leave a 5 star rating if you were satisfied with my assistance. thank you and good luck. you can always request me in the future.

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Customer reply replied 1 year ago
From what I have read, the regulated voltage control will drop the alternator output to 12.5-13.1 volts when engine is in fuel economy mode. Turn on head lights or tow mode, it turns this "feature" off.The following is a GM tech bulletin:Document ID#(###) ###-####
2007 GMC Truck Yukon XL Denali--------------------------------------------------------------------------------Subject: Voltmeter Gage Fluctuation - keywords battery charge camper cluster electrical excessive fluctuation gage gauge generator intermittent ipc lamp light low operation trailer towing tow volt voltage wire #PIT3331D - (07/27/2007)Models: 2005-2008 Cadillac Escalade, ESV, EXT2005-2008 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe2005-2008 GMC Sierra, Sierra Classic, Yukon, Yukon XL, Yukon Denali, Yukon Denali XLwith Regulated Voltage Control (RVC)--------------------------------------------------------------------------------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 / utility vehicle. 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 "Fuel Economy 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.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

this is true. forgot about that dang economy mode

david craig
david craig, Owner/[email protected] 3D Atuomotive
Category: GMC
Satisfied Customers: 4,194
Experience: owner/mechanic at 3D Automotive
Verified
david craig and 87 other GMC Specialists are ready to help you
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Customer reply replied 1 year ago
I never knew it existed! I've worked on my cars (always old junkers) since moving out on my own and was banging my head on the wall over this. Thanks again for your help.
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david craig
david craig
david craig, Owner/[email protected] 3D Atuomotive
Category: GMC
Satisfied Customers: 4,194
4,194 Satisfied Customers
Experience: owner/mechanic at 3D Automotive

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