12 V Starting and Charging
5-9
The Generator provides a PWM 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 Generator
field duty cycle signal (Generator F-terminal) is a PWM
signal of 60
–
460 Hz with a duty cycle of 0
–
100%.
Normal duty cycle is between 5
–
100%. 0
–
5% is
reserved for diagnostic purposes.
As the charging systems works to maintain the battery
charge and manage vehicle electrical loads, it is normal
for the voltmeter gauge on the instrument cluster or the
system voltage displayed in the DIC to fluctuate or
change. This does not indicate a malfunction.
Depending on the battery state of charge and the
vehicle electrical load, these values may be anywhere
from 12.5 V to 15.5 V.
Charging System Modes
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:
•
Windshield wipers are ON for more than 3 s.
•
Climate Control Voltage Boost Mode Request is
true, as sensed by the HVAC control module via
serial data. 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%.
•
Vehicle speed is greater than 145 km/h (90 mph)
•
A current sensor malfunction exists.
•
System voltage is 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 A and greater than
−
8 A,
and the battery state-of-charge is greater than or equal
to 80%. Its targeted generator output voltage is the
open circuit voltage of the battery and can be between
12.5
–
13.1 V. When fuel economy mode is active, the
generator is not charging, only maintaining open circuit
battery voltage. 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
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 s.
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 headlamps 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 Cluster Operation
Charge Indicator Operation
The instrument 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 ECM detects that the generator output is less
than 11 V or greater than 16 V. The instrument
cluster receives a serial data message from the
ECM requesting illumination.
•
The instrument cluster determines that the system
voltage is less than 11 V or greater than 16 V for
more than 30 s. The instrument cluster receives a
serial data message from the BCM indicating
there is a system voltage range concern.
•
The instrument cluster performs the displays test
at the start of each ignition cycle. The indicator
illuminates for approximately 3 s.
Driver Information Center 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 displayed when a charging system
DTC is a current DTC. The message is turned off when
the conditions for clearing the DTC have been met.
Voltmeter Gauge and/or System Voltage Display (if
equipped)
As a means of displaying the charging system
functions, some vehicles may be equipped with a
voltmeter gauge on the instrument cluster and/or a
system voltage display in the driver information center.
These will indicate the current vehicle system voltage.
As the charging systems works to maintain the battery
charge and manage vehicle electrical loads, it is normal
for the voltmeter gauge on the instrument cluster or the
system voltage display in the driver information center
to fluctuate or change. This does not indicate a
malfunction. Depending on the battery state of charge
and the vehicle electrical load, these values may be
anywhere from 12.5 V to 15.5 V.
2021 - Silverado 4500HD, 5500HD, and 6500HD Electrical Body Builder Manual
