2013 Chevrolet Silverado 1500 5.3L 70k
Road trip today I notice my voltage is low. I monitored closely thereafter, 10 to 20 minutes later voltage climbs back to normal. Holds there for a while, then drops again and holds there.
What’s up? Voltage regulator in alternate going bad?
Do I need to fix ASAP or will it wait a few hundred miles when I’m back home after the weekend?
Thanks
I’m pretty sure that what your explaining is normal. Its a computer controlled alternator. If the electrical load is low it will shut off periodically until voltage gets low enough then it will turn back on. Both of the gm trucks I own do it.
I forgot to ask if the red battery light is/ was on? If your charging system stops working that light will come on almost immediately.
you may have a battery going bad and eating up all of the extra juice the alternator is putting out,hence the low readings and normal readings.
yes,the alternator is computer controlled but it should be showing full voltage all of time,especially when running the air conditioner.
cant remember if that truck use the Valeo brand of alternator or not,if it does they usually arent worth rebuilding and you end up buying new.
if you take it to the shop and the battery tests good,have them scan the computer to see if the computer is turning the “L” terminal on and off normally,if it is the alternator is bad,have that verified with a load test.
good luck fishblood!! I know you dont need any troubles with a holiday coming up !!
Was the needle in the red or was it still in the middle (white?) color? My ‘16 does the same but stays in the white. White should be normal operation. Red is not.
No warning lights or anything.
I was driving with Windows open and no a/c.
One picture showing it at low. Other normal.
CameraZOOM-20180629110239875.jpg
CameraZOOM-20180629110900213.jpg
sent you a pm
Perfectly normal. It’s the on demand charging system working as designed.
Perfectly normal. It’s the on demand charging system working as designed.
munchy no disrespect intended,the voltage should never show below a fully charged batteries voltage.
the pic shows around eight volts,these newer systems need a minimum of twelve point six volts to operate correctly.
remember,you are supplying the engines computer and all of its monitored components,a body module that monitors the abs system,windows,lights,seat belts,a/c,etc.
add the transmission controller and its functions,many speed sensors,shift solenoids,,if it is 4×4,add the transfer case and the front diff,,etc.
these systems demand the best the battery and alternator can put out all of the time every time.
bad grounds,faulty gauges,bad batteries,poor connections anywhere can affect the volt meters readings,it needs checked out.
after all of that and no intention to derail the thread,whatcha been cooking lately Munchy???
On the bright side, your thermostat works great!
On the bright side, your thermostat works great!
<div class=”d4p-bbt-quote-title”>Munchy wrote:</div>
Perfectly normal. It’s the on demand charging system working as designed.munchy no disrespect intended,the voltage should never show below a fully charged batteries voltage.
the pic shows around eight volts,these newer systems need a minimum of twelve point six volts to operate correctly.
remember,you are supplying the engines computer and all of its monitored components,a body module that monitors the abs system,windows,lights,seat belts,a/c,etc.
add the transmission controller and its functions,many speed sensors,shift solenoids,,if it is 4×4,add the transfer case and the front diff,,etc.these systems demand the best the battery and alternator can put out all of the time every time.
bad grounds,faulty gauges,bad batteries,poor connections anywhere can affect the volt meters readings,it needs checked out.after all of that and no intention to derail the thread,whatcha been cooking lately Munchy???
No disrespect, but where do you see 8 volts???
The lowest reading on the gauge is 9 volts (stone dead battery), and the needle isn’t anywhere near it.
To the op, I wouldn’t worry a out a thing, unless you think it’s a new issue.
I had a 2013 5.3 Silverado and remember seeing the gauge move around as needed.
<div class=”d4p-bbt-quote-title”>iowaboy1 wrote:</div>
<div class=”d4p-bbt-quote-title”>Munchy wrote:</div>
Perfectly normal. It’s the on demand charging system working as designed.munchy no disrespect intended,the voltage should never show below a fully charged batteries voltage.
the pic shows around eight volts,these newer systems need a minimum of twelve point six volts to operate correctly.
remember,you are supplying the engines computer and all of its monitored components,a body module that monitors the abs system,windows,lights,seat belts,a/c,etc.
add the transmission controller and its functions,many speed sensors,shift solenoids,,if it is 4×4,add the transfer case and the front diff,,etc.these systems demand the best the battery and alternator can put out all of the time every time.
bad grounds,faulty gauges,bad batteries,poor connections anywhere can affect the volt meters readings,it needs checked out.after all of that and no intention to derail the thread,whatcha been cooking lately Munchy???
No disrespect, but where do you see 8 volts???
The lowest reading on the gauge is 9 volts (stone dead battery), and the needle isn’t anywhere near it.
To the op, I wouldn’t worry a out a thing, unless you think it’s a new issue.
I had a 2013 5.3 Silverado and remember seeing the gauge move around as needed.
I understand your question as the gauge clearly has a nine volt low side and a nineteen volt high side.
I am going by what the voltage reading is by what it is reading below fourteen volts,if you divide the lines by quarters of the gauge,it is showing around eight volts in its operating range or close to it.
I have been at this long enough to know that factory gauges are only a guideline regardless of what the dial says.
and you are correct,if battery voltage is too low,it should not run,however,if the alternator is doing its job,it will continue to run as the voltage is there to make sure it does,but,the gauge can only show what the battery is putting out while it is sucking up excess voltage from the alternator due to an internal short while it keeps running,hope that makes sense.
in other words,if the battery is okay,the gauge will show the excess the alternator is generating,this is where you will see the higher readings,ie,fourteen volts and above.
sorry,I am not a teacher and cant explain how I understand things,sure wish I could.
My last Tahoe and Yukon has always done that. My research into also what munchy eluded to.
munchy no disrespect intended,the voltage should never show below a fully charged batteries voltage.
That gauge in the pic is reading around 13volts. Like I said, it’s how the system was designed. When I first got my truck a few months back I noticed the exact same thing, did a little googlin and found the internet is full of threads just like this one. As long as there are no warning lights and it stays between the white marks you are good.
A little light readin….
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 (if equipped).
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 (if equipped), which is integrated to obtain net amp
hours.
If equipped with a battery current sensor, the electrical power management
function is also 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 (if equipped), the battery positive voltage
circuit, and estimated battery temperature to determine battery state of charge.
The ECM performs idle boost.
Battery Current Sensor (if equipped)
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.
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 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 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 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)
Battery current sensor fault exists (if equipped).
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.
Headlamp Mode
The BCM will enter Headlamp Mode when ever the headlamps 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.
Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculated ambient air
temperature is above 0°C (32°F). The calculated battery current is less than
1 ampere and greater than −7 amperes, and the generator field duty cycle is less
than 99 percent. Its targeted generator output voltage is 12.9 V. 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 68 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.
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. During cold weather warm-up and extreme
electrical demand , the generator capacity can be briefly exceeded causing this
message to be displayed for up to two minutes
after all of that and no intention to derail the thread,whatcha been cooking lately Munchy???
Unfortunately nothing, been too busy working and selling my house. Which once I receive the contract today will be sold. 
What the hell was that?
Alex,
I’ll take alternators for 100 please.
What the hell was that?
Shortened version…
Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculated ambient air
temperature is above 0°C (32°F). The calculated battery current is less than
1 ampere and greater than −7 amperes, and the generator field duty cycle is less
than 99 percent. Its targeted generator output voltage is 12.9 V. The BCM will
exit this mode once the criteria are met for Charge Mode.
Took to a mechanic in Currie MN Saturday morning.
Performed load test. Battery good.
They said the alternator was operating in spec but recommended I get it replaced.
This is a small town grungy shop.
Off to slayton to Napa. Old classmate of mine running register. They were out of alternators.
Go to sturdevants and they struggled to find the correct part number, needed VIN as there are two different amp rating alternators. They got the part number and zero in stock.
Off to Worthington to O Riley’s.
With the alternator on the desk clerk said “you know these will kick in and out and your gauge will go up and down” I then described what I was seeing.
This person was a service manager for 3 years at a Chevy dealership. He has seen this in and out of the shop many times. He mentioned that many people do not know this about the alternators.
He opened the box to show me how it cycles and immediately noticed this one does not have that feature.
So per his reccomodation and others on this forum I left without an alternator.
If I am reading my gauge correctly I’m barely dropping below 13V when it does drop.
It doesn’t stay low for long and it creeps back up.
I’m due for an oil change and I’ll have my local mechanic in Hastings verify battery and alternator this week.
What munchy posts seems to correlate with what I am seeing as well as what the service manager (now orileys parts salesman) describes as well.
Truck has not missed a beat in the 4-5 hours of driving since noticing the voltage drop.
Ran a/c on the 3.5 he drive yesterday and voltage fluctuated much less than when I’m doing the same trip without a/c.
I’m no mechanic, an engineer yes, so I’m just taking information from all parties and forming my own conclusion on how to proceed.
I’ll have the mechanic this week check the “L” terminals cycling as I did not confirm the Currie mechanic did that, despite telling them I wanted a load test and check to see if L terminals are cycling on/off.
Thanks y’all.
It’s normal, I had a 2010 and now a 2014 that do the same thing. Spoke with GM dealers on it and SilveradoSierra.com guys all told me within 2 minutes it’s normal.
My 2012 does the same. It worried me when I first noticed it, but it’s never caused an issue.
My 07 Suburban does the same thing. You can verify; the next time you see it drop turn on the tow / haul mode; that will return the voltage to “normal” in short order.
I have had an 05, 08, 11, 14, and a 15 year GM product. The 05 I noticed this and every time I would check it it was ok. Took it to the dealer as it was still in warranty. They did some checking and found out it is kinda “on demand charging”. I was the first one to notice it and bring it to the dealers attention. All of the above models all act the same way.
You must be logged in to reply to this topic.
