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, the clutch pedal position sensor, the manual transmission neutral position switch and engine speed to determine Autostart and Autostop conditions. The ECM also controls the auxiliary coolant 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.
Clutch Pedal Position Sensor
For vehicles with a manual transmission, the ECM monitors the clutch pedal position sensor for partial and fully depressed conditions. A partially depressed clutch pedal will cause the ECM to restart the engine during an Autostop condition if the transmission is in the Neutral position If the transmission is determined to be in gear, the ECM will not restart the engine until the clutch pedal is fully depressed.
Neutral Position Switch
The manual transmission, neutral position switch is used to determine if the transmission is in gear. The ECM will not allow Autostop until the clutch is engaged, the transmission is in the neutral position and then the clutch is fully disengaged.
Coolant Pump Motor
The ECM will turn on the auxiliary coolant pump motor during Autostop to maintain engine operating temperature and also maintain HVAC temperature. Once the engine is running, the ECM will turn off the coolant pump motor.
Body Control Module (BCM)
The body control module (BCM) monitors the Autostop mode switch in order to enable or disable the system. It is also the master of the low speed communication bus and transfers the appropriate messages to the instrument cluster and the HVAC.
Batter Sensor Module
The ECM monitors the battery sensor module for battery state of current, state of health, and battery charge via the data communication bus. If the battery is determined to be in poor state of health or having a low charge, the ECM will not allow Autostop to occur.
Autostop Mode Switch
The switch can disable the Autostart system if desired. Autostart is enabled at every ignition cycle.
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 point at the Autostop (500 RPM point) indicating the engine has been shut down by the Stop/Start System. Once the engine is restarted, or the Autostop mode button has disengaged Autostop, the tachometer will function normally.
Stop/Start Capacitor Control Module (SSCCM)
The SSCCM switches in the stop/start capacitor during an engine start to provide a boosted voltage This ensures stabilization of the power supply network during engine restarts. The SSCCM is capable of controlling the charging and discharging of the stop/start capacitor and also monitors it (e.g. internal temperature). The SSCCM communicates to the ECM.
Stop/Start Capacitor
The stop/start capacitor consists of two double layer capacitors which are switched in series to the standard battery for high battery discharge currents (Autostart). The high voltage drop caused by high currents during engine restart events are compensated by the additional voltage provided by the two double layer capacitors. The stop/start capacitor is switched in an out by the stop/start capacitor control module.