12-V Battery
The following information is for the 12 V battery only.
For information about charging the high voltage drive motor batteries, refer to
Starter/Generator Description and Operation.
Electrical Power Management (EPM) Overview
The electrical power management (EPM) system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems. This EPM system primarily utilizes existing on-board computer capability to
maximize the effectiveness of the charging system, manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The EPM system performs 3 functions:
| • | It monitors the battery voltage and estimates the battery condition. |
| • | It takes corrective actions by 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 (SOC) of the battery is determined by measuring the open-circuit voltage. The SOC 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 SOC 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 SOC based on adjusted net amp hours, battery capacity, initial SOC, 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 EPM function is designed to perform regulated voltage control (RVC) to improve battery SOC, battery life, and fuel economy. This is accomplished by using knowledge of the battery SOC and temperature to set the charging voltage to an optimum
battery voltage level for recharging without detriment to battery life.
Charging System Components
Generator Control Module
| • | The generator control module, also referred to as the starter generator control module, is a serviceable GMLAN device located under the hood, toward the front of the vehicle on the drivers side. It is connected to the vehicles 12 and 36-volt DC power
circuits, and it is also joined to the starter-generator by 3-phase AC cables. The generator control module is cooled by engine coolant, which is circulated through a cold plate. A separate, electrically driven pump is used to ensure adequate coolant flow, and
individual coolant inlet and outlet hoses connect the cold plate to the cooling system. The generator control module performs three main functions: |
| • | As the power inverter for the starter-generator, the generator control module converts 36-volt DC power into 3-phase AC power to drive the starter-generator as a motor. The power inverter also rectifies 36-volt AC output power from the starter-generator
into the 36-volt DC power used to charge the 36-volt generator battery. |
| • | An auxiliary power module contained within the generator control module converts 36-volt DC power into the 12-volt DC power which is used for 12-volt vehicle loads and to charge the underhood 12-volt battery. A serviceable 175 Amp Fuse (GM P/N 15305191)
located beneath the generator control module DC cable terminal box cover protects the vehicles 12-volt electrical system from excessive current. The generator control module contains a Renesas M32 processor, and it directly controls the starter-generator, transmission
auxiliary oil pump, hill-hold solenoids, auxiliary coolant pump and the generator control module coolant pump. The pumps and solenoids are driven by 12-volt pulse width modulated (PWM) power through vehicle wiring harnesses. |
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 (IPC) for electrical power management (EPM) operation. The BCM determines the desired voltage set
point and sends the information to the APM. The BCM monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge (SOC).
Battery Current Sensor
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-V 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)
The ECM receives control decisions based on messages from the BCM.
Instrument Panel Cluster (IPC)
The IPC provides a means of customer notification in case of a failure and a voltmeter. There are 2 means of notification, a charge indicator and a driver information center (DIC) message of SERVICE BATTERY CHARGING SYSTEM.
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
The BCM will enter this mode when the interpreted charging system voltage is less than 13.2 V for 30 minutes. When this condition exists the BCM will enter Normal Mode for 5 minutes. The BCM will then determine which mode to enter
depending on voltage requirements.
Normal Mode
The BCM will enter Normal 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). |
| • | Vehicle Speed is greater than 145 km/h (90 mph) |
| • | Current Sensor Fault Exists |
| • | System Voltage was determined to be below 12.56 V |
| • | Tow/Haul Mode is enabled |
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 ambient air temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is greater than -8 amps but less than 5 amps, and the
battery state of charge (SOC) is greater than or equal to 85 percent. Its targeted APM set-point voltage is the open circuit voltage of the battery and can be between 12.6-13.2 V. The BCM will exit this mode and enter Normal Mode when any
of the conditions described above are present.
Headlamp Mode
The BCM will enter Headlamp Mode when ever the high or low beam headlamps are ON. Voltage will be regulated between 13.9-14.5 V
Voltage Reduction Mode
The BCM will enter Voltage Reduction Mode when the calculated battery temperature is above 0°C (32°F) and the calculated battery current is greater than -7 A but less than 1 A. Its targeted APM set-point voltage is 12.9-13.2 V.
The BCM will exit this mode once the criteria are met for Normal Mode.
Plant Assembly Mode
The BCM will increase charging voltage for the first 500 miles of operation in an effort to ensure that the 12 V battery is fully charged when the vehicle is delivered to the customer.
Instrument Panel Cluster (IPC) Operation
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 system voltage less than 11 V or greater than 16 V. The IPC receives a GMLAN message from the ECM requesting illumination. |
| • | The BCM determines that the system voltage is less than 11 V or greater than 16 V. |
| • | 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. |
SERVICE BATTERY CHARGING SYSTEM
The BCM and the ECM will send a GMLAN message to the DIC for the SERVICE BATTERY CHARGING SYSTEM message to be displayed. It is displayed whenever the charge indicator is commanded ON due to a failure.
