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Alternator

RobC

New Member
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Location
California
Thread starter #1
i have a 05 GMC Yukon Denali My Voltmeter runs between 9-10 but when I turn my headlights on it goes to 14 and stays there. I did replace the alternator with one from Napa and it did the same thing. Any thoughts
 

smokymtn65

Well-Known Member
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Location
East TN
#6
You can, best if you have probes with alligator clips or something to hold in place so you can watch the read out on volt meter and gauge at same time. there should be an exposed positive lug on you fuse box may be easier than going to alternator.
 

WarWagon

Well it hits on 7 of 8...
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AZ
#7
First thought is everything is normal for the goofy RVC GM used for these years. The "OMG!!! The alternator quit I am going to walk" volt meter reading is common and normal. Really need a deep cycle battery in these rigs. GM cuts the alternator out to save fuel when the battery is charged and the loads are low. Headlights on bring the voltage up for brighter headlights. Many modes.

https://noln.net/2017/03/28/battery-management-challenges-smart-system/

You might need to service the gauge cluster as the swatch gears used are all shot. Known issue for these years.

Yes, get a real voltmeter or one that plugs into the cigarette lighter that reads volts. (Idiot light style are useless and are sold.) Harbor Freight is good enough. Measure voltage at the battery etc. FORGET ABOUT THROWING PARTS AT IT LIKE ALTERNATORS!!!
 

THEFERMANATOR

FRANKENBURBAN
Staff member
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Staff #10
First thought is everything is normal for the goofy RVC GM used for these years. The "OMG!!! The alternator quit I am going to walk" volt meter reading is common and normal. Really need a deep cycle battery in these rigs. GM cuts the alternator out to save fuel when the battery is charged and the loads are low. Headlights on bring the voltage up for brighter headlights. Many modes.

https://noln.net/2017/03/28/battery-management-challenges-smart-system/

You might need to service the gauge cluster as the swatch gears used are all shot. Known issue for these years.

Yes, get a real voltmeter or one that plugs into the cigarette lighter that reads volts. (Idiot light style are useless and are sold.) Harbor Freight is good enough. Measure voltage at the battery etc. FORGET ABOUT THROWING PARTS AT IT LIKE ALTERNATORS!!!
That system was NOT used until the LML IIRC, and even then it was NOTHING like what was used in gassers to satisfy CAFE standards. The only input the ECM or any other controller has on an LLY is to supply the alternator field after the engine has started, and monitor the charge output to turn on the battery light in case of under voltage or no alternator output. So disregard EVERYTHING in regards to the rvc. I don't think GM even used that system on anything but 1500 and down.

As to the OP, get a voltmeter and see what actual voltage is. Steppers in the cluster often fail in 03-05 trucks. If your voltage was truly that low, I would expect all kinds of alarms from the DIC.
 

WarWagon

Well it hits on 7 of 8...
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#11
@THEFERMANATOR o_O Pretty sure a "05 GMC Yukon Denali" the OP is working on is a 1/2 ton and not a diesel. The headlights going on and higher voltage reading is a good clue it has the RVC system.

It never hurts to test the battery and clean grounds as the system is hard on batteries. However the volt gauge swings are large with the system so again may be normal. That's one gauge GM should have numbed to "idiot light" from the get go.
 

THEFERMANATOR

FRANKENBURBAN
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Staff #12
@THEFERMANATOR o_O Pretty sure a "05 GMC Yukon Denali" the OP is working on is a 1/2 ton and not a diesel. The headlights going on and higher voltage reading is a good clue it has the RVC system.

It never hurts to test the battery and clean grounds as the system is hard on batteries. However the volt gauge swings are large with the system so again may be normal. That's one gauge GM should have numbed to "idiot light" from the get go.
Oops, I seen 05 and thought lly, but I'm not sure if the rvc system even made it to 6.0l's(most Denali's I've seen have been 6.0l's, but I know some got the l33 5.3l). Last I heard from Ben it was only 4.8/5.3l that got the system. It was only models that fell under the cafe standards that got it. I would have to pull a tune file on one to see if it's enabled or not.
 
Last edited:

RobC

New Member
Messages
7
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8
Location
California
Thread starter #13
Oops, I seen 05 and thought lly, but I'm not sure if the rvc system even made it to 6.0l's(most Denali's I've seen have been 6.0l's, but I know some got the l33 5.3l). Last I heard from Ben it was only 4.8/5.3l that got the system. It was only models that fell under the cafe standards that got it. I would have to pull a tune file on one to see if it's enabled or not.
 

RobC

New Member
Messages
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8
Location
California
Thread starter #14
So I put a multimeter on the battery it read 12.3 when I started car it went to 14.4 and when I turned on lights and heater it went to 14.7 so now I'm assuming it's the gauge cluster. Does that make sense or should I check something else ??
 

WarWagon

Well it hits on 7 of 8...
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#15
12.3v is low for a battery being around 70% charged. So you have a bad worn out battery, drain that is discharging the battery, or are not getting it charged up enough. How old is the battery? (Hot weather like Bakersfield means a 2-3 year battery life.) I assume this 12.3v is with only a dome light on? Other higher loads can make the reading off. You want to see 12.6 to 12.8v for a fully charged battery. (Higher is ok if you just charged it.) Charge the battery overnight. Test voltage again. Or have the battery tested. eliminate the battery and it's connections before getting into the charging system.
 

RobC

New Member
Messages
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Location
California
Thread starter #16
The 12.3 is with nothing on just battery by itself. The battery is prob 5 yrs old and alternator is fairly new. We live in hot weather (Tracy, CA) but not as hot as Bakersfield I will replace battery and see how the voltmeter on dash does

Thanks War
 
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