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Old 10-31-2007, 09:58 PM   #1
slowwrench
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Default Dropping volt meter


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07 Tahoe, volt meter drops to about 9 volts after about 15 miles. no symptoms of lo voltage though. Bad gauge?
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Old 10-31-2007, 11:09 PM   #2
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If you can check the voltage at the battery (when your gauge is reading 9 volts) this may help point you in the right direction.

If the battery reads around 12volts (12.5 - 14v engine running), I would suspect the gauge or something on that circuit.

If the battery reads the same 9volts, I would suspect the battery or alternator.
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Old 11-03-2007, 12:58 AM   #3
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The new Tahoes cut the alternator when the battery doesn't need it to drop the load on the engine.
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Old 11-03-2007, 01:55 AM   #4
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Quote:
Originally Posted by 73shark View Post
The new Tahoes cut the alternator when the battery doesn't need it to drop the load on the engine.
But if that's the case, how is the electrical system and all the loads surviving on the 9 volts his gauge indicates? If voltage diminishes, then the current draw needs to be higher in order to maintain the same level of electrical power output. This is why car manufacturers are slowly making the switch over to 42 volt systems soon. Higher voltage equals less current draw for the same amount of output(wattage). Less current draw means smaller gauge wire and less weight in vehicles. This is one way engineers are planning for better fuel economy on future vehicles.
If the alternator shuts off, then the electrical system is running strictly off the battery while the engine is running. Not only does that affect the electrical system, but engine operation as well. That means lower voltage to the ignition system and coils, less spark output, and less overall engine efficiency. Has GM engineered something completely different recently?
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Old 11-03-2007, 07:34 AM   #5
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SO the volt meter should drop, but to where on the gauge? It's above the red, so is this what one should expect?

Thanks for the help.:thumbsup:

Now if I can just get it to accept the tire position changes after I rotated the tires, I'll be set.
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Old 11-04-2007, 12:51 AM   #6
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2007 tahoe take it back to the dealer still under factory warranty the screw with the electrnics on this tahoe my friend had the whole electronic brain go out on his 06 tahoe had it warrantied cost 7000.00 to replace whole thing!!
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Old 11-04-2007, 01:02 AM   #7
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7000.00! :eek2: :eek2: :eek2:
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Old 01-18-2008, 01:37 PM   #8
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I just got my 2008 Tahoe back from the dealer for the same issue. It seems the service writer hadn't heard of this either. It's very disconcerting... Especially as it didn't exhibit this behavior for the first 3 to 4 weeks of ownership. Perhaps it doesn't do it until it hits the 1000 mile mark? Not sure what my mileage was when I first noticed it, but it was probably close as I have 1200 now a week or so later.

I asked the service writer how would I know if there's a problem with the charging system if it regularly fluctuates from 12V to 15V? He said it'll probably drop to 10V and the truck won't run anymore. I asked why GM put a gauge in if it's not gonna be of any help? I'll know that I have a problem when I break down!! He had no answer to this. I think I'd have preferred an idiot light instead!

They gave me a copy of GM Document ID# 2042756, but the following is copied from a previous post and says nearly the same thing:

Document ID# 2000522
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, EXT

2005-2008 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005-2008 GMC Sierra, Sierra Classic, Yukon, Yukon XL, Yukon Denali, Yukon Denali XL

with 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


© Copyright General Motors Corporation. All Rights Reserved.


--------------------------------------------------------------------------------
Document ID# 2000522
2007 GMC Truck Yukon XL Denali
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Old 01-18-2008, 06:26 PM   #9
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Is it an isolated incident, or does it do it all the time?
Mine does it every so often, but no charging issues.
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Old 01-19-2008, 12:53 AM   #10
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It does it approx every third time I drive the truck. My trips are generally 20 to 30 minutes. Once it's down around 12.5V it doesn't go back up to 14 until I shut it off and start it again. Then it usually runs high around 15V for a few minutes until it settles down to either 14V or 12.5V.

I hooked up a digital multimeter to a cigarette plug so I could get an accurate reading of the voltage. It doesn't seem to drop below 12.4V or go higher than 15V when the engine is running. It typically seems to be in the high 12s to low 13s. When I take a longer drive I'll let you know how it behaves...

Still, it's completely opposite of what I've known normal to be for the past 20+ years of driving. It doesn't give that warm and fuzzy feeling that everything is ok. I hope GM does something with this in the future... I'd even prefer a false reading on the gauge unless it falls below "normal" operating range. Perhaps they could remove the numbers from the gauge face and put a green area in the center and red areas at the ends of the scale... or just get rid of the gauge altogether and use an trouble light...

As to JKmotorsports issue of dropping to 9V I'd say he has a problem. You should bring it in for further evaluation.

Last edited by Bugsy68; 01-19-2008 at 01:09 AM.
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