Alternator behavior on newer GM vehicles.

[HHR]

I have a friend who just got a 2007 Chevy Avalanche and his voltage gauge has been fluctuating from 12.6-14.2 and down again while he is driving. Is this caused by the computer sensing less load on the electrical system and letting the alternator "freewheel" or is this a sign of internal regulator failure?
When I got my 2008 Chevy Impala, I noticed the same thing while I had my ScanGauge plugged in driving down the highway (Impala has no gauge on dash).

 

[whistlepig]

My 2007 Z71 gauge does this. According to the owners manual it's supposed to. It makes the gauge hard, if not impossible, to figure out what the alternator is really doing.

 

[Dmace]

Perfectly normal, it's called RVC (Regulated Voltage Control) and it will vary the alternator load based on demand. This was first designed for the AFM (Active Fuel Management) system to help with loads while in 4-cyl mode. On the trucks, if you put it in Tow/Haul mode it will stay in RV charge mode and shouldn't drop below 13.9 volts. If you don't want to use the Tow/Haul mode just put on your headlights.
Here's the TSB that explains it better:

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


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.

 

[Ford850]

This is a perfect example of why there are idiot lights and gauges now. Real gauges cause so many concerns.

 

[pjbci]

I like the idiot lights to "save" an engine, but I want real gauges on my dash to let me kmow whats going on under the hood before a small problem becomes critical.

 

[WM75Guy]

Let me add this to my list of reasons for me to have diesel pickups. It would drive my wife nuts seeing the gauge bounce around and the I would have to get it fixed.

 

[HHR]

Thanks for the responses. My friend thought he was going to be stranded in the woods when he saw the voltage falling.

 

[David_Kb7uns]

I like the idiot lights to "save" an engine, but I want real gauges on my dash to let me kmow whats going on under the hood before a small problem becomes critical.

Then do not look at the oil pressure gauge on a newer Dodge Cummins because the computer runs the gauge and shows an expected oil pressure for the engine operating conditions.

David Kb7uns

 

[pjbci]

Thats crazy. If they gonna put one in there, it should be a real one.

 

[Dmace]

Then do not look at the oil pressure gauge on a newer Dodge Cummins because the computer runs the gauge and shows an expected oil pressure for the engine operating conditions.

David Kb7uns

The same can be said for any new diesel truck, they all use idiot gauges.