Charging voltage varies, alot....

trammd · January 17, 2019

I have a 2014 1500 LTZ Z71.

Brand new Battery installed AGM style 850CCA.

My charging voltage swings wildy. When I start up I get the alternator to battery charging voltage of 14.3 to 15.2 Volts. As the truck warms it will begin to fluctuate, I can watch the volt meter drop to 12.7 Volts (battery voltage) it isnt dependant on Loads, headlights. accessories etc. also not dependant on engine RPMs. It will drop to 12.7V then if I turn the truck off and restart it will start out at 14.7 V then after 3-4 minutes begin to drop...then after awhile it may return to 14+/

Really weird. The comman thread is by re-starting the truck it always starts at 14.4+ then after waiting it begins to drop.

any ideas?

The truck has 60K miles and the original alternator I believe.

Z45 · January 17, 2019

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.

From your owners manual page 5-16/17

Voltmeter Gauge
When the ignition is on, this gauge
indicates the battery voltage.
When the engine is running, this
gauge shows the condition of the
charging system. The gauge can
transition from a higher to lower or a
lower to higher reading. This is
normal. If the vehicle is operating
outside the normal operating range,
the charging system light comes on.
See Charging System Light on
page 5-21 for more information. The

voltmeter gauge may also read
lower when in fuel economy mode.
This is normal.
Readings outside the normal
operating range can also occur
when a large number of electrical
accessories are operating in the
vehicle and the engine is left idling
for an extended period. This
condition is normal since the
charging system is not able to
provide full power at engine idle. As
engine speeds are increased, this
condition should correct itself as
higher engine speeds allow the
charging system to create maximum
power.
The vehicle can only be driven for a
short time with the readings outside
the normal operating range. If the
vehicle must be driven, turn off all
accessories, such as the radio and
air conditioner.
Readings outside the normal
operating range indicate a possible
problem in the electrical system.
Have the vehicle serviced as soon
as possible.