Voltage gauge question 2010 Sierra 5.3

TJay74 · January 25, 2013

So have noticed for the vast majority of the time my gauge sits at 14v, the other day though for some reason it dropped down to 11.5-12v and stayed there for that entire key cycle until I stopped the truck.

Does anyone else notice or this on their trucks as well? Is there a rhyme or reason for it or is it something I need to start looking into and address now?

MS3DALE · January 25, 2013

Service Information

2010 Chevrolet Silverado - 4WD | Cheyenne, Sierra, Silverado VIN C/K Service Manual | Document ID: 2394671

#07-06-03-009B: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System and Concerns About Camper/Trailer Battery Charging - (Feb 5, 2010)

Subject: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System and Concerns About Camper/Trailer Battery Charging

Models: 2005–2010 Cadillac Escalade Models

2005–2010 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005–2010 GMC Sierra, Sierra Classic, Yukon Models

This bulletin is being revised to add the 2010 model year. Please discard Corporate Bulletin Number 07-06-03-009A (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 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.

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Gone Again · January 25, 2013

If this is on the 2001 you have listed I'd get the charging/battery system checked.

TJay74 · January 25, 2013

I have a 2010 GMC Sierra now, and this explaints it perfectly and makes sense.

Thanks everyone...Todd

bigjer2 · February 8, 2013

I have a 2010 GMC Sierra now, and this explaints it perfectly and makes sense.

Thanks everyone...Todd

Directly from Service Manual 2009 GMC Sierra 1500 ;

Charging System Operation

The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:

• Battery Sulfation Mode

• Charge Mode

• Fuel Economy Mode

• Headlamp Mode

• Start Up Mode

• Voltage Reduction Mode

The engine control module (ECM) controls the generator through the generator turn on signal. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 5 volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:

Commanded Duty Cycle

Generator Output Voltage

10%

11 V

20%

11.56 V

30%

12.12 V

40%

12.68 V

50%

13.25 V

60%

13.81 V

70%

14.37 V

80%

14.94 V

90%

15.5 V

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5 volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

Battery Sulfation Mode

The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 volts for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.

Charge Mode

The BCM will enter Charge Mode when ever one of the following conditions are met.

• The wipers are ON for more than 3 seconds.

• The GMLAN Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.

• The estimated battery temperature is less than 0°C (32°F).

• Battery state of charge is less than 80 percent.

• Vehicle speed is greater than 145 km/h (90 mph)

• Current sensor fault exists

• System voltage was determined to be below 12.56 volts

• Tow/Haul mode is enabled

When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9-15.5 volts, depending on the battery state of charge and estimated battery temperature.

Fuel Economy Mode

The BCM will enter Fuel Economy Mode when the ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amps and greater than -8 amps, and the battery state of charge (SOC) is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5-13.1 volts. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.

Headlamp Mode

The BCM will enter Headlamp Mode when the headlamps are ON. Voltage will be regulated between 13.9-14.5 volts

Start Up Mode

When the engine is started the BCM sets a targeted generator output voltage of 14.3 volts for 30 seconds.

Voltage Reduction Mode

The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F). The calculated battery current is less than 1 amp and greater than -7 amps, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 13 volts. The BCM will exit this mode once the criteria are met for Charge Mode.

Auxiliary Battery Charging (TP2)

The auxiliary battery provision (TP2) can be used to supply electrical power to additional equipment that the customer may choose to add, such as a slide-in camper or trailer, without discharging the vehicles primary battery. The auxiliary battery relay closes when the engine is running, in order to allow the generator to charge the auxiliary battery. The relay opens when the engine is off, so that the accessories will not discharge the vehicles primary battery, which is used for engine starting. If the vehicle is equipped with an auxiliary battery, the relay will be located on the driver's side of the vehicle, next to the underhood electrical center. Generally, a fuse should not be used in the STUD 1 Fuse 70 position of the underhood fuse block, if the vehicle is equipped with an auxiliary battery. A plastic plug may be installed in this position instead of a fuse. If a fuse is installed in this position, the accessories will discharge the primary battery in addition to the auxiliary battery.

<a name="ss4-1848193">Instrument Panel Cluster (IPC) Operation

Charge Indicator Operation

The instrument panel cluster (IPC) illuminates the charge indicator and displays a warning message in the driver information center (DIC) when the one or more of the following occurs:

• The engine control module (ECM) detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a GMLAN message from the ECM requesting illumination.

• The BCM determines that the system voltage is less than 11 volts or greater than 16 volts.

• The IPC receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

• The ignition is ON, with the engine OFF.

Battery Voltage Gauge Operation

The IPC displays the system voltage as received from the BCM over the GMLAN serial data circuit. If there is no communication with the BCM then the gauge will indicate minimum.

This vehicle is equipped with a regulated voltage control (RVC) system. This system turns off the generator when it is not required in order to improve fuel economy. The generator will turn back on when 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.

SERVICE BATTERY CHARGING SYSTEM

The BCM and the ECM will send a GMLAN message to the DIC for the SERVICE BATTERY CHARGING SYSTEM message to be displayed. It is commanded ON when a charging system DTC is a current DTC. The message is turned OFF when the conditions for clearing the DTC have been met.

Gurrzt · February 8, 2013

My 2013 Yukon Denali does the same thing, when the battery is charged the alternator "disengages" (voltage drops) to about 12V and stays there, when the battery needs charging the alternator "engages" and charges the battery.

00Silverado4x4 · February 8, 2013

Directly from Service Manual 2009 GMC Sierra 1500 ;

Charging System Operation

The purpose of the charging system is to maintain the battery charge and vehicle loads....

^^^What he said, normal operation.

beetle · February 8, 2013

This is all very good and interesting information. The simple way to determine if you have a charging problem is if your battery charge gets too low to crank the motor over, otherwise I would just ignore the gauge reading....keep it simple and don't overthink it.