Auto Stop/Start System

WARNING: This page is about a different variant/trim than selected.

If the Remote Function Actuator (RFA) detects a valid smart key, the driver can start the engine. When the ignition switch is operated, the Body Control Module/Gateway Module (BCM/GWM) transmits a hardwired crank request. The crank request is transmitted to the Powertrain Control Module (PCM).

When the PCM receives the crank request signal, the PCM energizes the starter relay to start the engine. When the motor solenoid is energized, it closes a high-current contact within the solenoid. The high-current contact supplies the starter motor with power from the startup battery through the Battery Junction Box (BJB).

When the auto stop/start system is active and the ambient temperature is above -5°C (23°F), the PCM uses the Belt Integrated Starter Generator (BISG) to crank the engine. When the PCM receives an engine restart request, the PCM sends a crank command to the BISG. The crank command to the BISG is sent through the High Speed (HS) Controller Area Network (CAN) power mode zero bus. The BISG starts the engine by turning the crankshaft through the BISG drive belt.

For additional information, Refer to: BELT INTEGRATED STARTER GENERATOR

NOTE: If the Belt Integrated Starter Generator (BISG) reports an error to the Powertrain Control Module (PCM) or the PCM cannot communicate with the BISG, the starter motor is used to start the engine.

The auto stop/start system is controlled by the PCM and the BCM/GWM through the FlexRay bus. Signals from other system components and modules are used to determine the correct conditions for system operation. The auto stop/start system detects when it is appropriate to stop and start the engine.

The auto stop/start system automatically stops the engine in appropriate conditions, resulting in zero exhaust emissions and saving fuel when the vehicle is stationary. When the driver is ready to move off, the engine instantly restarts. Sophisticated controls make sure that the auto stop/start system does not compromise the needs of either the driver or the vehicle.

By default the stop/start system is enabled at the start of each ignition cycle. The auto stop/start system can be enabled/disabled using the auto stop/start soft key.

Software within the PCM controls the operation of the stop/start system.

In addition to its own dedicated components the auto stop/start system encompasses many other vehicle systems such as:

Road speed.
The state of vital vehicle systems.
Environmental conditions.
Transmission Control Switch (TCS) position.

If all necessary conditions are satisfied, the stop/start system automatically stops the engine if:

The vehicle stops from a speed higher than 17 km/h (10.5 mph).
Sufficient pressure is applied to the brake pedal to make sure that the vehicle is stationary.
The transmission is in DRIVE or SPORT.
PARK or NEUTRAL is selected on the TCS.

When the engine stops, the auto stop/start indicator illuminates in the Instrument Cluster (IC) to tell the driver. Other warnings normally associated with an engine stoppage will not illuminate during the engine stop within an auto stop/start cycle. For example, the charge warning indicator and low oil pressure indicators are suppressed.

To restart the engine, the driver must release the brake pedal or press the accelerator pedal. Depending on ambient temperature, the PCM then operates the starter motor or the BISG to start the engine.

If system conditions are not approved by the PCM the auto stop/start system will not behave as expected.

For example:

System inhibit - The engine continues running even though the vehicle is stationary with the brake pedal pressed and the TCS in DRIVE or SPORT. Another condition is when the vehicle is stationary and the TCS is in PARK or NEUTRAL.
System override - The engine has been stopped by the auto stop/start system but conditions have since changed, this activates an early automatic engine restart.

These interventions make sure that the auto stop/start system does not impact on:

Vehicle and occupant safety.
Driver requirements.
Occupant comfort.
Vehicle on road and off road capabilities.

The main control logic for auto stop/start operation resides in the PCM. However the BCM/GWM has software to communicate engine stoppage inhibits to the PCM. In some instances the driver is notified of the reason for the intervention.

Stop Inhibitors

The following conditions prevent the auto stop/start system from stopping the engine.

Driver initiated stop inhibitors:

Driver disables the auto stop/start system.
Brake pedal not fully pressed.
Accelerator pedal pressed.
Hood is open.
Driver door is open.
Driver seatbelt is not fastened.
Climate control system operated above the calibrated threshold.
Windshield demist is operating.

Vehicle system initiated stop inhibitors:

Startup battery cold cranking capability below threshold.
Startup battery state of charge is low.
Catalytic converter outside either pre or post calibration range.
Engine coolant temperature below threshold.
Engine oil temperature below threshold.

Environmental initiated stop inhibitors:

Ambient air temperature above 40°C (104°F).
Ambient air temperature below -5°C (23°F).

Start Initiators

When the engine stops within an auto stop/start cycle the following conditions initiate an early restart within the same auto stop/start cycle.

Driver initiated start initiators:

Driver disables the auto stop/start system.
The accelerator pedal is pressed.
REVERSE gear is selected on the TCS.
Vehicle speed is above the calibrated threshold 3 km/h (2 mph). A restart only occurs if the transmission is in NEUTRAL and the driver is present. For example, the driver seatbelt remains fastened and the driver door remains latched.
A higher climate control blower speed is selected.
Windshield demist is activated.

Vehicle system initiated start initiators:

Windshield demist activates.
The passenger compartment temperature decreases below, or increases above the selected thresholds.

Environmental initiated start initiators:

Ambient air temperature rises above 40°C (104°F).
Ambient air temperature falls below -5°C (23°F).

The maximum engine stop duration is 270 seconds, the vehicle will restart after this duration.

Start Inhibitors

When the engine stops within a stop/start cycle, certain conditions prevent an automatic restart.

Driver initiated start inhibitors:

The hood is opened.
The driver seatbelt is disengaged. This is an automatic start inhibitor, therefore the engine can be restarted by the brake pedal being released or the accelerator pedal being operated.
The driver door is unlatched. This is an automatic start inhibitor, therefore the engine can only be restarted by the brake pedal being released or the accelerator pedal being operated.

Vehicle system inhibitor:

There is a system fault.