This normal?

[Jmiller11331]

Last night it was in the dead middle at 14 and now it's here...is this normal? It's a brand new truck. Maybe it's just me now noticing the gauge who knows


 
 
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[Donstar]

It definitely appears to be in the normal range which is what I'm sure you'll be told by your dealer.  Once it goes below, then take it in for warranty work. It will fluctuate and I wouldn't be concerned as it moves in the normal range.

[diyer2]

Normal.

My 2012 reads low sometimes.

No problems.

 

[Squished]

Looks fine to me.  When my Duramax starts it's at or below the left most line.  After about 2 minutes it goes up over 14.

[Justin101714]

Variable charging. Normal.


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[Jmiller11331]

Thanks guys


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[2017SierraSLT]

It's certainly refreshing to have functional gauges with NUMBERS. Look at these competitors clusters..

 

RAM

 

 

FORD

 

 

TUNDRA.    At least the voltage gauge uses numbers, but why not extend that to the temp and oil pressure? Look at that faux wood too!!

 

 

TITAN...

 

 

[BigBadSierra]

The charging system only gives the battery what it needs. If it's low it will kick it up and give it more.  If the battery is charged it falls into more of a trickle charge mode.

It's way better for the battery then the old days when the more you revved the engine the more more power it sent to the battery.

 

All of the electronics draw bad on all modern vehicles without the variable  charging batteries would be dying left and right.

[LSR Mike]

and 13.8 VDC is nominal voltage for a current automotive system.

[redwngr]

From GM Upfitter publications:

 

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. 

Also says to expect voltmeter variation:

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.

 

 

 

[redwngr]

And, also from GM upfitter publications:
 

In the GM 2018 upfiitter guides there is lots of information about the charging modes and idle boost that can be created by the charging system.

I stumbled across the write up -- it is multiple pages of info. 

Starts around page 4-17. 
File is big - adobe reader says over 1100 pages

https://www.gmupfitter.com/files/med..._2017AUG31.pdf

There are 6 different charging modes it can use. 
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode

There are also 4 different levels of 'idle boost' that the charging system can use. 

Electrical Power Management Description and Operation (Diesel)

The electrical power management is used to monitor and control the charging system and alert the driver of possible problems within the charging system. 

The electrical power management system makes the most efficient use of the generator output, improves the battery state‐of‐charge, extends battery life, and manages system electrical loads.

The load shed operation is a means of reducing electrical loads during a low voltage or low battery state‐of‐charge condition.

The idle boost operation is a means of improving generator performance during a low voltage or lowbattery state-of-charge condition. 

Idle boost consists of three steps:
idle boost 1, idle boost 2, and idle boost 3
(approximately 750, 900, and 1050 rpm respectively).

Idle boost is activated in incremental steps, idle boost 1 must be active before idle boost 2 can be active.

Each electrical power management function, either idle boost or load shed, is discrete. No two functions are active at the same time. The criteria used by the body control module (BCM) to regulate electrical power management are outlined below:

The alternator output is controlled by the BCM, and there is a charge of the % output it can be asked to run at, and the resulting output voltage from each step. 

This is clearly not the charging system control method many of us learned in auto shop. 

The engine control module (ECM) controls the generator through the generator turn ON signal circuit.
The ECM monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 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). 

[Jmiller11331]

And, also from GM upfitter publications:
 
In the GM 2018 upfiitter guides there is lots of information about the charging modes and idle boost that can be created by the charging system.
I stumbled across the write up -- it is multiple pages of info. 
Starts around page 4-17. 
File is big - adobe reader says over 1100 pages
https://www.gmupfitter.com/files/med..._2017AUG31.pdf

There are 6 different charging modes it can use. 
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode
There are also 4 different levels of 'idle boost' that the charging system can use. 
Electrical Power Management Description and Operation (Diesel)
The electrical power management is used to monitor and control the charging system and alert the driver of possible problems within the charging system. 
The electrical power management system makes the most efficient use of the generator output, improves the battery state‐of‐charge, extends battery life, and manages system electrical loads.
The load shed operation is a means of reducing electrical loads during a low voltage or low battery state‐of‐charge condition.
The idle boost operation is a means of improving generator performance during a low voltage or lowbattery state-of-charge condition. 
Idle boost consists of three steps:
idle boost 1, idle boost 2, and idle boost 3
(approximately 750, 900, and 1050 rpm respectively).
Idle boost is activated in incremental steps, idle boost 1 must be active before idle boost 2 can be active.
Each electrical power management function, either idle boost or load shed, is discrete. No two functions are active at the same time. The criteria used by the body control module (BCM) to regulate electrical power management are outlined below:
The alternator output is controlled by the BCM, and there is a charge of the % output it can be asked to run at, and the resulting output voltage from each step. 
This is clearly not the charging system control method many of us learned in auto shop. 
The engine control module (ECM) controls the generator through the generator turn ON signal circuit.
The ECM monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 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). 

Great information, thank you


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[chrispassas21]

From GM Upfitter publications:
 
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. 

Also says to expect voltmeter variation:
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.
 
 

 

Thanks for that info! Good to know.


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