2008 GMC Sierra Pick Up Truck

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charbaby

charbaby

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My buddy Dan just bought a new 08 Sierra Pick up truck with a 5.3 L V-8 w/ cylinder deactivation. This truck is supposed to be set up for towing/hauling/plowing. He plans to use this truck for snow plowing so he went for a new plow as well. Now, since the plow wiring and hydrolics have been installed(even without the plow being on the truck at this time), the needle on his dashboard amp gague is now reading in the minus rather than in the center of the gague OR to the plus side. This happens even while driving! Dan has taken the truck back to the place of installation and has been given information...(being told that "THEY ALL DO THAT"). Dan claims that the amp gague did not read this way prior to taking the truck in to the plow shop. Dan says "I NOTICE THINGS LIKE THAT". He claims that the gague needle was either straight up or to the plus side of the gague when he took new delivery of the truck just several weeks ago, up until the plow hardware was installed. Although, more & more people in Dan's circle(plow buddies)are noting similar gague readings just not as drastic as Dan is claiming. His plow buddies also said that they didn't really notice the gague reading until Dan had mentioned it to them. Dan doesn't notice any dimming lights at night when this happens(even when stopped at a RED signal light) but, he is just concerned since he never noticed this in any of his other plow trucks either.

Can someone PLEASE explain this better to me so that I can relay some information onto my buddy Dan. It's driving him crazy and he wants to make sure that everything is OK before this upcomming winter and while the truck and plow are still under warranty. Only weeks old!

Thanks in advance to all and any help is appriciated.

CB
 
That is weird. If there is no load on the alternator and the battery is in good shape, should be showing a positive charge.
 
Boy... where do I start? A factory amp gauge is basically a worthless tool. It upsets me (not the word I want to use) to see a amp gauge on a vehicle because it so worthless. Not all auto manufactures are this stupid. Its intended purpose is to measure current flow to the battery. Think of it as a fuel flow gauge on a fuel system. On the surface it does not sound like a bad idea.

One of the bigger problems is accuracy, for the amp flow gauge to have a chance to be accurate you would have to direct ALL current flow from the alternator output under the dash to the amp gauge with large gauge wire in and out. For obvious safety reasons to those inside the vehicle factory gauges are NOT wired that way.

There are other issues with amp gauges. Even if they were done correctly an amp gauge does not necessarily give you the whole picture.

The bottom line is get a GOOD Volt gauge such as a Auto Meter. A volt gauge would be the electrical equivalent to a fuel pressure gauge on fuel system.
 
Hirev - I feel the same way. A voltmeter is FAR more useful than an amp meter in a car.
But there seems to have been a change for the worse in this vehicle. I wish I had before/after voltmeter readings!
Pulling fuses and disconnecting wires from the new system can help trace down where the offender is.
 
There are valid arguments for voltmeters instead of ammeters in cars, yours isn't one of them.

Quote:
One of the bigger problems is accuracy, for the amp flow gauge to have a chance to be accurate you would have to direct ALL current flow from the alternator output under the dash to the amp gauge with large gauge wire in and out. For obvious safety reasons to those inside the vehicle factory gauges are NOT wired that way.


That's not how they work. Ammeters have a shunt in them that handles the high current flow, the meter itself only handles a small fraction of the total current.

A shunt can be located anyplace in the car, it doesn't have to be in the meter. The positive battery cable (excluding the starter cable) is a good place to put a shunt. Or, the cable itself can be used as a shunt.
 
Read the owners manual. It tells you the alternator does not charge the battery when it is not needed.

The alternator has it's own computer under the hood to manage this feat.

PS-This didn't just start happening when he had a snow plow installed.
 
Originally Posted By: XS650
There are valid arguments for voltmeters instead of ammeters in cars, yours isn't one of them.

Quote:
One of the bigger problems is accuracy, for the amp flow gauge to have a chance to be accurate you would have to direct ALL current flow from the alternator output under the dash to the amp gauge with large gauge wire in and out. For obvious safety reasons to those inside the vehicle factory gauges are NOT wired that way.


That's not how they work. Ammeters have a shunt in them that handles the high current flow, the meter itself only handles a small fraction of the total current.

A shunt can be located anyplace in the car, it doesn't have to be in the meter. The positive battery cable (excluding the starter cable) is a good place to put a shunt. Or, the cable itself can be used as a shunt.



And there lies the potential problem. If the ammeter does use an external shunt the new wiring for the plow MIGHT have changed the resistance value which would cause the ammeter to be inaccurate.

I would try this to see if that's the case: Start the truck and let it idle. Note ammeter reading immediately after starting. Watch it as the battery is charged. If it slowly drifts further negative that might indicate the shunt resistance has changed and the ammeter will no longer read 0 when the system is fully charged.

If my suspicions are correct if you disconnect the plow wiring I'll bet the ammeter now reads correctly.
 
Originally Posted By: Johnny
Has he been back to the GMC dealer to get their opinion?


Johnny,
No, he has not been back the the dealership yet. I suggest this to him.


PS-This didn't just start happening when he had a snow plow installed. [/quote]

MrCritical,
Yes, according to my buddy! It does seem that it has. Or, are you saying that this is normal?

The bottom line is get a GOOD Volt gauge such as a Auto Meter. A volt gauge would be the electrical equivalent to a fuel pressure gauge on fuel system.

Hirev,
I made a mistake! It is a volt meter not an amp gague. My appologies, I used the wrong term. Everything else remains the same.
[/quote]
 
MrCritical,
Thanks for staying with me on this subject! Yes, he is going to read the OM as I suggested to him. I don't see/talk to him everyday so, when he or I call the other to talk we'll find out more information.

Thanks to everyone who has responded. I'll post again soon.
 
Originally Posted By: MrCritical
Read the owners manual. It tells you the alternator does not charge the battery when it is not needed.

The alternator has it's own computer under the hood to manage this feat.

PS-This didn't just start happening when he had a snow plow installed.



You beat me to it. It is called the RVC system and GM started using it a few years back as a fuel econonmy enhancement. Also extends battery life. Only charges when needed.
 
These little innovations are fascinating. I think this is a brilliant idea. Probably only makes a small difference, but 8 or 10 little ideas like this could add up to significant increases in efficiency.

Nice job, GM!
 
Here's some more info courtesy of a TSB:


Service Information 2008 Chevrolet Silverado - 2WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID: 2170219
--------------------------------------------------------------------------------

#07-06-03-009A: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System and Concerns About Camper/Trailer Battery Charging - (Jul 21, 2008)


Subject: Information On Voltmeter Gauge Fluctuation Due To Regulated Voltage Control System And Concerns About Camper/Trailer Battery Charging


Models: 2005-2009 Cadillac Escalade Models

2005-2009 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005-2009 GMC Sierra, Sierra Classic, Yukon Models




--------------------------------------------------------------------------------

This bulletin is being revised to add the 2009 model year. Please discard Corporate Bulletin Number 07-06-03-009 (Section 06 -- Engine/Propulsion System).


--------------------------------------------------------------------------------

Voltmeter Fluctuation Condition
Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or 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 of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator 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 that 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.

Camper/Trailer Battery Charging Concerns
Some customers may comment that when towing or hauling a camper/trailer, the auxiliary battery for the camper/trailer will not stay charged. In most cases, this concern is blamed on the new RVC system. While the RVC system does reduce the generator's targeted output voltage to 12.6-13.1 volts when in "Fuel Economy Mode", this feature is bypassed if the tow/haul feature is enabled. With the tow/haul feature enabled, the RVC system will stay in "Charge Mode" and the targeted generator output voltage will be 13.9-15.5 volts, depending on the battery state of charge and the estimated battery temperature. To keep the generator in the "Charge Mode", use either of the following two methods.

• The first method is to use the tow/haul mode when towing or hauling a camper or trailer.

• The second method is to turn on the headlights, which will increase the generator's targeted output voltage to 13.9-14.5 volts.

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


© 2008 General Motors Corporation. All rights reserved.
 
Interesting, I read that on the latest BMW's there are a number of fuel saving measures like this. One of them includes that the alternator only charges (unless the battery is low) when the car is off-throttle, which increases engine braking and doesn't use any horsepower when cruising. This is basically a software/hardware change that is good for some fraction of an MPG.
 
Originally Posted By: mrsilv04
"Regulated Voltage Control System"?

No thanks! I'm glad that I have a 2004 model.



Oh come on, technology dude. You want the extra battery life and .0001 mpg don't ya? :))
 
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