Hummer H3. Manual — part 69

The ECM provides information over the serial data circuit to the generator battery control
module. The generator battery control module monitors the following data parameters provided
by the ECM:

Intake air temperature

Fuel grams per second

Throttle position

Engine cooling fan speed

Engine coolant temperature

Exterior Environment - Outside Air Temperature

The generator battery control module uses these data parameters for different charging system
modes depending on the required voltage needed.

Instrument Panel Cluster (IPC)

The instrument panel cluster (IPC) provides a means of customer notification in case of a failure.
There are two means of notification, a battery charge indicator and a driver information center
message of SERVICE CHARGING SYSTEM FAILURE and CHARGING SYSTEM FAULT.

Charging System Operation

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

Charge Mode

Fuel Economy Mode

Voltage Reduction Mode

Start Up Mode

Headlamp Mode

Battery Sulfation Protection Mode

Windshield Wiper Voltage Boost Mode

Fuel Pump Voltage Boost Mode

De-Ice Voltage Boost Mode

The generator battery control module monitors the generator performance though the generator
field duty cycle signal circuit, the generator field control circuit, and the battery positive voltage
circuit. The generator battery control module controls the generator through the generator field

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

control, charge indicator control, circuit. The signal is a 5-volt pulse width modulation (PWM)
signal of 128 Hz +/- 5 percent with a duty cycle of 0-100 percent. The duty cycle sent by the
generator battery control module is limited between 36-90 percent. When the engine is turned
OFF, the module will send 0 percent duty cycle, low voltage. When there is loss of
communication with the ECM, the module will send 100 percent duty cycle, 13.8 volts. The
following table shows the commanded duty cycle and output voltage of the generator:

The generator provides a feedback signal of the generator voltage output through the generator
field duty cycle signal circuit to the generator battery control module. 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.

Charge Mode

The generator battery control module will enter Charge Mode when at least one of the following
conditions is met:

The electric cooling fans are on high speed.

The rear defogger is ON.

The battery state of charge is less than 80 percent.

The battery current is not between -8 and +15 amps.

The estimated ambient air temperature is less than 0°C (32°F).

DTC B1516 is set.

Once one of these conditions are met the generator battery control module will set the targeted
generator output voltage to the nominal optimum battery voltage which is from 13.9-15.5 volts,
the voltage set point is based on the batteries state of charge and estimated battery temperature.

Commanded Duty Cycle

Generator Output Voltage

10%

11.0 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

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

The battery voltage ramps up to the targeted set point at a rate of 20 mV per second.

Fuel Economy Mode

The generator battery control module will enter Fuel Economy Mode when all of the following
conditions are true:

Estimated ambient air temperature is equal to or greater than 0°C (32°F).

The calculated battery current is less than +15 amperes and greater than -8 amperes.

The battery state of charge is greater than or equal to 80 percent.

The rear defoggers are turned OFF.

The electric cooling fans are on low speed or OFF.

The targeted generator output voltage is 13 volts. The generator battery control module will exit
this mode once the criteria are met for Charge Mode or it will boost voltage to a pre-determined
set point for the fuel pump, headlamps, or windshield wipers.

Voltage Reduction Mode

The generator battery control module will enter Voltage Reduction Mode when the calculated
ambient air temperature is above 0°C (32°F). The calculated battery current is less than 2
amperes and greater than -7 amperes, the generator field duty cycle is less than 99 percent. The
rear defoggers are turned OFF, and the electric cooling fans are on low speed or OFF. Its
targeted generator output voltage is 87 percent of the Charge Mode set point but limited to 12.9
volts. The generator battery control module will exit this mode once the criteria are met for
Charge Mode or it will boost voltage to a pre-determined set point for the fuel pump, headlamps,
or windshield wipers.

Start Up Mode

After the engine has started the generator battery control module sets a targeted generator output
voltage of 14.5 volts for 30 seconds.

Headlamp Mode

The generator battery control module will enter the Headlamp Mode when the headlamps, low or
high beams, are turned ON. The voltage will ramp up or down to 14.5 volts at a rate of 10
mV/second. The module will exit this mode once the headlamps are turned OFF and enter Charge
Mode, Fuel Economy Mode, or Voltage Reduction Mode.

Battery Sulfation Mode

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

The generator battery control module will enter this mode when the interpreted generator output
voltage is less than 13.2 volts for 45 minutes. Once in this mode the generator battery control
module will set the targeted output voltage to the nominal optimum battery voltage, see Charge
Mode, for 3 minutes. The generator battery control module will then determine which mode to
enter depending on vehicle conditions.

Windshield Wiper Voltage Boost Mode

When the generator battery control module is in Fuel Economy Mode or Voltage Reduction
Mode, the module will boost battery voltage to 14.5 volts when the windshield wipers are ON,
intermittent, low, or high speed, after 8 seconds. The voltage will ramp to 14.5 volts at a rate of
50 mV/second. The module will exit this mode once the Windshield Wipers are OFF for 5
seconds and the module will enter Charge Mode, Fuel Economy Mode, or Voltage Reduction
Mode.

Fuel Pump Voltage Boost Mode

When the generator battery control module is in Fuel Economy Mode or Voltage Reduction
Mode, the module will immediately boost battery voltage to 13.4 volts when the instantaneous
fuel flow is greater than 21k grams/second and the throttle position sensor pedal position is
greater than 90 percent. The module will exit this mode once the instantaneous fuel flow is less
than 5k grams/second and enter Charge Mode, Fuel Economy Mode, or Voltage Reduction
Mode.

De-Ice Voltage Boost Mode

The generator battery control module will enter De-Ice Voltage Boost Mode when the estimated
ambient air temperature is less than or equal to -1°C (+30°F) and the engine coolant temperature
is less than or equal to 75°C (167°F). The module will be in Charge Mode if the above conditions
are true. Once the engine coolant temperature becomes greater than 75°C (167°F), the module
will remain in Charge Mode or enter Fuel Economy Mode or Voltage Reduction Mode based on
the vehicle conditions.

Instrument Panel Cluster (IPC) Operation

Charge Indicator Operation

The instrument panel cluster (IPC) illuminates the charge indicator in the message center when
the one or more of the following occurs:

IMPORTANT: The generator battery control module is not set up to set a DTC if

the battery voltage is too high or too low. Check with the ECM to

2008 Hummer H3

2008 ENGINE Engine Electrical - H3