ok i have another NON spyder related question

[cuznjohn]

on my new car i have a volt gauge, when i first got the car the volts showed over 14 volts all the time. now it shows that when i first start the car it is doing 14 volts, then it drops down to 12 to 13 volts. then it will jump to over 14 volts again, then back down. as far as i am concerned there is something wrong, but according to the shop foreman who just called me, it is ok and working just right. any of you that have voltage gauges in your cars or trucks, what do they show. i just went out and did another short video of the gauge to show you what i am talking about. he sent me the instructions on how it works, and that he gets calls all the time about it. here are the instructions, and as soon as i get the video downloaded to youtube, i will post it also.,,,,, thanks for any information you can give me.

Charging System Description and Operation
Electrical Power Management Overview
The electrical power management system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This electrical power management system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The electrical power management system performs 3 functions:
· It monitors the battery voltage and estimates the battery condition.
· It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
· It performs diagnostics and driver notification.
The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the state-of-charge of the battery is determined by measuring the open-circuit voltage. The state-of-charge is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The state-of-charge can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout ignition-on, the algorithm continuously estimates state-of-charge based on adjusted net amp hours, battery capacity, initial state-of-charge, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to improve battery state-of-charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state-of-charge and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the electrical power management. The second section describes charging system operation. The third section describes the instrument panel cluster operation of the charge indicator, driver information center messages, and voltmeter operation.
Charging System Components
Generator
The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 V.
Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster for electrical power management (electrical power management) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge. The BCM performs idle boost.
Battery Current Sensor (If applicable)
The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates 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.
Battery Sensor Module (If applicable)
The BCM monitors the battery sensor module for battery state of current, state of health, and battery charge via the data communication bus. If the battery is determined to be in poor state of health or having a low charge, the BCM will not allow the ECM to Autostop.
Engine Control Module (ECM)
When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator field duty terminal is connected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from the BCM.
Instrument Panel Cluster
The instrument panel cluster provides the customer notification in case a concern with the charging system. There are 2 means of notification, a charge indicator and a driver information center message of SERVICE BATTERY CHARGING SYSTEM if equipped.
Charging System Block Diagram


Serial Data - GMLAN Low Speed
Hard-Wired
P16 Instrument Cluster
K20 Engine Control Module
G13 Generator
M64 Starter Motor
C1 Battery
B18 Battery Current Sensor
K9 Body Control Module
B110 Battery Sensor Module

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
· Head lamp Mode
· Start Up Mode
· Voltage Reduction Mode
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). The signal is 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 V 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.
· 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 V
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 V, depending on the battery state of charge and estimated battery temperature.
Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the estimated battery 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 amperes and greater than −8 amperes, and the battery state-of-charge 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 V. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.
Head lamp Mode
The BCM will enter Head lamp Mode when ever the head lamps are ON (high or low beams). Voltage will be regulated between 13.9–14.5 V.
Start Up Mode
When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 seconds.
Tow/Haul Mode (If applicable)
Pressing the Tow/Haul Mode button located on the center stack, the vehicle system voltage is raised and the remote(non-vehicle) battery will be charged. Having the headlights on will raise the system voltage and if the Tow/Haul button is applied it will not serve any purpose. The voltage is regulated between 13.9-14.5 V.
Instrument Panel Cluster Operation
Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a warning message in the driver information center if equipped, when the one or more of the following occurs:
· The engine control module (ECM) detects that the generator output is less than 11 V or greater than 16 V. The instrument panel cluster receives a GMLAN message from the ECM requesting illumination.
· The instrument panel cluster determines that the system voltage is less than 11 V or greater than 16 V for more than 30 seconds. The instrument panel cluster receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern.
· The instrument panel cluster performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
Display Message: BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY CHARGING SYSTEM
The BCM and the ECM will send a serial data message to the driver information center for the BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or 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.
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Information




2017 GMC Truck Acadia (VIN N) | Acadia VIN N Service Manual 9371116 | Engine/Propulsion | 12 V Starting and Charging | Description and Operation | Document ID: 2809645

---

Charging System Description and Operation

Electrical Power Management Overview
The electrical power management system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This electrical power management system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The electrical power management system performs 3 functions:
·It monitors the battery voltage and estimates the battery condition.
·It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
·It performs diagnostics and driver notification.
The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the state-of-charge of the battery is determined by measuring the open-circuit voltage. The state-of-charge is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The state-of-charge can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout ignition-on, the algorithm continuously estimates state-of-charge based on adjusted net amp hours, battery capacity, initial state-of-charge, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to improve battery state-of-charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state-of-charge and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the electrical power management. The second section describes charging system operation. The third section describes the instrument panel cluster operation of the charge indicator, driver information center messages, and voltmeter operation.
Charging System Components
Generator
The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 V.
Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster for electrical power management (electrical power management) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge. The BCM performs idle boost.
Battery Current Sensor (If applicable)
The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates 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.
Battery Sensor Module (If applicable)
The BCM monitors the battery sensor module for battery state of current, state of health, and battery charge via the data communication bus. If the battery is determined to be in poor state of health or having a low charge, the BCM will not allow the ECM to Autostop.
Engine Control Module (ECM)
When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator field duty terminal is connected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from the BCM.
Instrument Panel Cluster
The instrument panel cluster provides the customer notification in case a concern with the charging system. There are 2 means of notification, a charge indicator and a driver information center message of SERVICE BATTERY CHARGING SYSTEM if equipped.
Charging System Block Diagram


Serial Data - GMLAN Low Speed

Hard-Wired

P16 Instrument Cluster

K20 Engine Control Module

G13 Generator

M64 Starter Motor

C1 Battery

B18 Battery Current Sensor

K9 Body Control Module

B110 Battery Sensor Module





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
·Head lamp Mode
·Start Up Mode
·Voltage Reduction Mode
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

[Bob Denman]

Cuzn...

[cuznjohn]

https://www.youtube.com/watch?v=8mx4xwgyqtk

[cuznjohn]

Cuzn...

it is just that the little things get to me, that's all

[Bob Denman]

I know...

And I'm certainly not trying to make it sound as if you're "making a mountain out of a hole-hill".
I just think that the readings that you see don't look all that far from what should be expected; if at all...
At least I didn't tell you to put a piece of electrician's tape over the gauge!

[Easy Rider]

First, posting ALL of that content accomplished exactly nothing because almost nobody will actually look at it all.

Second, the alternator contains a voltage regulator. It makes the voltage go up when the battery needs a charge and when the electrical load is high.
It lets the voltage go down when the battery is fully charged and the electrical load is low.

It absolutely SHOULD vary like that but.......but it should never go below 12.8 volts or so because that is the raw battery voltage.

Your question is a perfect example of why most car makers removed the charging system and temperature gauges and replaced them with "idiot lights". Too many people worried about the movement of the gauges and what was "normal".

[ARtraveler]

Hang in their John, and pay no mind to the background noise.

I am not technical enough to give you an answer other than I think that is the way it is supposed to be. Don't quote me on that though.

[Bob Denman]

First, posting ALL of that content accomplished exactly nothing because almost nobody will actually look at it all.

Thread Police.jpg

[cuznjohn]

First, posting ALL of that content accomplished exactly nothing because almost nobody will actually look at it all.

Second, the alternator contains a voltage regulator. It makes the voltage go up when the battery needs a charge and when the electrical load is high.
It lets the voltage go down when the battery is fully charged and the electrical load is low.

It absolutely SHOULD vary like that but.......but it should never go below 12.8 volts or so because that is the raw battery voltage.

Your question is a perfect example of why most car makers removed the charging system and temperature gauges and replaced them with "idiot lights". Too many people worried about the movement of the gauges and what was "normal".

lol i figured no one would read it. i post a lot of stuff on here, and some don't know when i am kidding or not. so i posted what they sent me. as for the idiot lights, i can also understand that. i can't remember the last time i had a volt gauge in a car. but the first 3 weeks it was always over 14 volts, then all of a sudden it started dropping. so that is what made me think something was wrong.

[Bob Denman]

Cuzn,
I LIKED it!

[JerryB]

Hi Easy Rider,

Re: Your question is a perfect example of why most car makers removed the charging system and temperature gauges and replaced them with "idiot lights".

^^^^^^ This.

You beat me to it.

Jerry Baumchen

[MercerLake]

More info than most of us need, but the shop foreman is right it is functioning as designed. Most of those functions are to decrease the load on the engine from the charging system when it isn't needed, saves gas! And the battery should last longer also.

[hypurone]

Perfectly normal. My 2010 Camaro does this. I can get it to go right back up from just over 12v to 14+ volts just by crankin' up the tunes! Yes, I have a serious system in the car....

[Bob Denman]

Hi Easy Rider,

Re: Your question is a perfect example of why most car makers removed the charging system and temperature gauges and replaced them with "idiot lights".
^^^^^^ This.
You beat me to it.
Jerry Baumchen

But some of us DO enjoy the security blanket afforded by excessive amounts of information...

Worried.jpg

[cuznjohn]

ok i know some think i am nuts. but i talked to a friend last night in florida and sent him the video of what mine does. he has a 2017 pick up gmc and said he has never seen his do what mine did. i don't want to buy a new battery just to prove if i am right or wrong, so i put my anti gravity jumper in the car for now, just in case

[Easy Rider]

but the first 3 weeks it was always over 14 volts, then all of a sudden it started dropping. so that is what made me think something was wrong.

Hopefully that means that you finally rode it enough to get the battery fully charged.

It probably will go back up there for a while if the machine sits for a few days.

[Easy Rider]

he has a 2017 pick up gmc and said he has never seen his do what mine did.

Now we are comparing spyders to trucks ?? (apples to oranges)

Another case of "If I've never seen it then it obviously doesn't exist."

The ONLY time that meter will give you even the slightest clue as to the health of the battery itself is when you first turn it ON but before you start the engine. At that point, it should be at least 12.6 volts.......unless it's been sitting for a while and then it might be a bit lower.

If the voltage reading at that point starts to slowly creep down over time, then either you are not riding enough OR the battery is getting weak.

The readings at ALL times while the engine is running is a test of the charging system and NOT the battery.

[cuznjohn]

being you mentioned spyders, when i put a volt gauge on my spyder, it always showed 13 to 14 volts. i really don't care much what happens, i am covered, it is a new SUV. i just get upset that to try and see what is going on, they don't change the battery.

[Bob Denman]

John,
Do you also have an ammeter? They might actually give you a more useful indication of the health of the charging system.

[cuznjohn]

i will have to look bob, i am pretty sure it does. i just went out to the car to check to see how the rain deflectors go on. first two times the dealer put them on, they broke,. so i told them to take the second broken set off, and give me the new set that i will do. to open the windows to look, i see i lost all the settings again. the seat went all the way forward, the set setting were changed when i pressed the button to return, the phone was disconnected, and the ac was not on auto. so either they now do something, or i call GMC, tell them everything, and have them tell me about another dealer i can go to. i am fed up

[Bob Denman]

Are these deflectors sitting in the window track? It often helps to warm them up with a hair dryer, before trying to bend them into place.

[cuznjohn]

well believe it or not, i e mailed them again and told them about everything changing in the settings in the car. guess what i got a e mail sent back saying, I THINK WE HAVE TO CHECK THAT OUT FOR YOU. i wrote back and said, ASK COLLEEN THE SERVICE WRITER, I TOLD HER ABOUT IT TWICE SO FAR. so now i am waiting to hear from them again. AMAZING

[Bob Denman]

It sounds as if Colleen is getting a lump of coal for Christmas this year.
at least they have responded!