Rick's Free Auto Repair Advice

Voltmeter fluctuates GM Trucks

The voltmeter fluctuates on my GM Truck

GM has issued a technical service bulletin #07-06-03-009 regarding Voltmeter fluctuates GM Trucks. GM says fluctuating voltage on the vehicle’s voltmeter is NORMAL and is not a reason to replace any parts. The TSB applies to 2005-08 Cadillac Escalade, 2005-08 avlanche, Silverado, Silverado Classic, Suburban, Tahoe, 2005-08 GMC Sierra, Sierra Classic, and Yukon.

The charging systems in these vehicles do not use an alternator decoupler to increase gas mileage. Instead they incorporate a Regulated Voltage Control (RVC) system. The RVC is controlled by the PCM and adjusts the amount of “field” to the generator. The purpose of the RVC system is to eliminate charging when it is not needed in order to improve fuel economy.

The targeted voltage in these system ranges from 12.6-13.1 volts when the system is in “Fuel Economy Mode.” As soon as the PCM detects that the system needs additional power generation, it exist this mode and moves into “Charge Mode” at normal charging rates. So the vehicle owner may notice a fluctuation in the voltage meter from 12 to 14 volts. This is NORMAL. Do NOT replace any charging system components.

Some of these vehicles have a “tow/haul feature.” When this feature is enabled, the charging system bypasses the economy mode and the generator output should be in the 13.9 to 15.5 volts range, depending on the stat of charge of the battery and the battery temperature.

You can force the system into Charge Mode by switch into the tow/haul mode, OR
simply turn on the vehicle’s headlights. That will increase the generator’s output to 13.9 to 15.5 volts.


© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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