System Components
Engine Control Module (ECM)
The engine control module (ECM) monitors the inputs from the engine coolant temperature (ECT) sensor, vehicle speed sensor (VSS), hood ajar switch, brake booster vacuum sensor, Battery Sensor Module (BSM - Via GMLAN), Analog Battery Current Sensor, the brake pedal position sensor, the accelerator pedal position sensor, and engine speed to determine Autostart and Autostop conditions. The ECM also controls the auxiliary coolant pump motor for cabin heating and the auxiliary transmission fluid pump motor.
Transmission Control Module (TCM)
The transmission control module monitors the inputs from the transmission neutral safety switch to determine the driver selected gear. This information is transmitted to the ECM via serial data to support the Auto Stop Start algorithm.
Engine Coolant Temperature sensor
The ECT sensor is used to determine engine operating temperature.
Intake Air Temperature Sensor
The ECM uses this sensor to monitor ambient air temperature. If too cold, the Autostop will not occur.
Inside Air Temperature Sensor
The HVAC control module monitors the passenger compartment temperature sensor to determine the temperature inside the passenger compartment. The HVAC control module sends this temperature reading to the ECM on the data communication circuit. The ECM uses this temperature values to determine if a restart is requires based on the temperature inside the passenger compartment.
Vehicle Speed Sensor
The vehicle speed sensor is used to determine vehicle speed. If vehicle speed is detected above a calculated value during an Autostop condition, the ECM will start the engine.
Hood Ajar Switch
If the hood switch is in the open position, the vehicle will not Autostop. If the hood is opened during Autostop, the vehicle will automatically restart.
Brake Booster Vacuum Sensor
The ECM monitors vacuum in order to ensure proper power assist for the brake pedal. If the ECM determines vacuum is too low, it will restart the engine.
Brake Pedal Position Sensor & Accelerator Pedal Position Sensor
The ECM monitors both the brake pedal position sensor and the accelerator pedal position sensor to determine the level of activation for each. While the accelerator pedal is in it's at rest position with no pressure applied by the operator, a partially depressed Brake pedal will cause the ECM to prepare the engine for an Autostop event. When the vehicle is in an auto stop event and the status of the brake pedal position sensor changes from meeting the autostop criteria to not meeting this criteria the engine will be restarted provided all of the other conditions to allow an autostart are met. If the Accelerator pedal is moved from its at rest position the vehicle will also enter an auto start event if all other conditions to support an autostart event, except for the brake pedal position, are met.
Transmission Gear Shift Position Switch
The transmission gear shift position switch is used to determine if the transmission is in the proper state to allow an auto stop/start event. The ECM will not allow Autostop until the brake is engaged, the transmission is in the forward gear position and then the vehicle slows to below the minimum speed required to allow and autostop while meeting all of the other minimum criteria to support an autostop event.
Auxiliary Transmission Oil Pump
The ECM will turn on the auxiliary transmission oil pump motor during Autostop to provide the transmission with the proper fluid pressures required to maintain correct transmission functionality required to support Auto Start drive away shifting. Once the engine is running after an auto stop, the ECM will turn off the auxiliary transmission pump motor.
Coolant Pump Motor
The ECM will turn on the auxiliary coolant pump motor during Autostop to help the cabin temperature when required based upon the HVAC system settings. Once the engine is running after an auto stop, the ECM will turn off the coolant pump motor.
Body Control Module (BCM)
The body control module (BCM) monitors the Intelligent Battery Sensor over LIN and transmits the information from these devices to the ECM over high speed GMLAN serial data communications. The BSM provides battery voltage and current to the ECM for use in the Battery State Estimation system. The BCM is also the gateway for the vehicles two primary serial data communication busses and transfers the appropriate messages to and from the instrument cluster and the HVAC system related to stop start functionality.
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 ECM. 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
The BCM monitors the battery sensor module information on battery voltage and current, state of health, state of function and battery state of charge via the LIN data communication bus. Information on the battery current and voltage is transferred through the gateway in the BCM to the ECM for use in the battery state estimation system in the ECM. Other data provided to the BCM by the sensor is used within the BCM to determine the proper control levels of the battery charging system. If the battery is determined to be in a low state of charge (<75%), the ECM will not allow the vehicle to enter an Autostop event.
Instrument Cluster
In order to differentiate between a normal engine shut down (engine speed 0 RPM) and when the engine has been shut down by the Stop/Start System, the tachometer needle will rest at the Autostop indicator icon (500 RPM point) indicating the engine has been shut down by the Stop/Start System. Once the engine is restarted, the tachometer will function normally.
Primary 12V Battery
This battery is the primary energy storage device for vehicle. It powers vehicle at all times except during starting when an auxiliary battery powers all vehicle loads except the starter.
Auxiliary 12V Battery
This is an auxiliary energy storage device for vehicle. It powers the vehicle loads, except the starter, during engine cranking (e.g. starter motor engaged).
Dual Battery Control Module (DBCM)
The DBCM is used to isolate 12V primary battery from vehicle loads during cranking events. It switches primary and auxiliary batteries in and out at appropriate times to support vehicle loads and battery charging. It does not utilize vehicle bus communication. The following table defines the utilization of the primary and auxiliary batteries based on specified events.
| Event | Primary Battery | Auxiliary Battery |
|---|---|---|
| Key off | Yes | No |
| Key on | Yes | Yes |
| *Key Crank | No | Yes |
| Run | Yes | Yes |
| Auto-stop | Yes | No |
| *Auto-start | No | Yes |
| *During a Key Crank or Auto-start event, the primary battery supplies power to the Starter Motor. | ||