Auto Stop/Start System

WARNING: This page is about a different car, the 2019 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.

At the beginning of a drive cycle, when the stop/start switch is operated, the auto stop/start system operates in the same way as on vehicles without stop/start.

The auto stop/start system is controlled by the Powertrain Control Module (PCM) and the Body Control Module/Gateway Module (BCM/GWM) assembly via High Speed (HS) Controller Area Network (CAN) powertrain systems bus messages and signals from other system components and modules 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 tailpipe emissions and saving fuel that would otherwise be used idling the engine when stationary. When the driver is ready to move off, the engine instantly restarts. Sophisticated controls ensure that the 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 switch in the floor console. The Light Emitting Diode (LED) in the auto stop/start switch is extinguished when the stop/start system is disabled.

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. Complex technology interconnects these systems and ensures all the necessary conditions are satisfied by monitoring, among others:

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

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

The vehicle stops from a speed greater than 4 km/h (2.5 mph).
Sufficient pressure is applied to the brake pedal to ensure the vehicle is stationary and the transmission is in D (Drive) or S (Sport), or the vehicle is stationary and P (Park) or N (Neutral) selected on the TCS.

The driver will be notified that the engine stops by the auto stop/start warning indicator being illuminated in the Instrument Cluster (IC). Other warnings normally associated with an engine stoppage, for example the ignition and low oil pressure indicators, are suppressed so will not illuminate during an engine stoppage in a stop/start cycle.

To restart the engine, the driver simply releases the brake pedal or presses the accelerator pedal. The PCM then operates the starter motor and starts the engine.

If system conditions are not approved by the PCM the auto stop/start system will not behave as expected, examples of this are:

System inhibit: the engine will continue running even though the vehicle is stationary with the brake pedal pressed and the TCS in D (Drive) or S (Sport), or the vehicle is stationary and the TCS is in P (Park) or N (Neutral).
System override: the engine has been stopped by the stop/start system but conditions have since changed, this will activate an early automatic engine restart.

These interventions are to ensure the auto stop/start system does not impact on:

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

Although the main control logic for stop/start operation resides in the PCM the Body Control Module/Gateway Module (BCM/GWM) assembly has software to communicate engine stoppage inhibits to the PCM. In some instances, depending on the reason for the system intervention the driver will be notified, via the message center, of the reason for the intervention.

Stop Inhibitors

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

Driver effected stop inhibitors:

Driver switches off the auto stop/start system
A steering wheel paddle switch has been used to select a gear
Brake pedal not fully pressed
Accelerator pedal depressed
Hood is open
Driver door is open
Driver seatbelt is not fastened
Climate control system used above calibrated threshold
Windshield demist is operating
Trailer electrical connection detected.

Vehicle system effected stop inhibitors:

Brake booster vacuum below threshold
Battery cold cranking capability below threshold
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 effected stop inhibitors:

Ambient air temperature above 40 °C (104 °F)
Ambient air temperature below 0 °C (32 °F).

Start Initiators

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

Driver effected start initiators:

Driver switches off the stop/start system
The accelerator pedal is pressed
A steering wheel paddle switch is operated to select a gear
Reverse (R) is selected on the TCS
Vehicle speed above calibrated threshold 3 km/h (2 mph) (a restart will only occur if the transmission is in neutral and the driver is present, for example, the driver seatbelt remains fastened and the driver door remains latched)
Brake booster vacuum below threshold (driver operating brake pedal)
A higher climate control blower speed is selected
Windshield demist is activated.

Vehicle system effected start initiators:

Battery cranking capability is near its lower threshold
Battery state of charge is near its lower threshold
Windshield demist activates
The passenger compartment temperature decreases below or increases above the selected thresholds.

Environmental effected start initiators:

Ambient air temperature rises above 40 °C (104 °F)
Ambient air temperature falls below 0 °C (32 °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 will prevent an automatic restart:

Driver effected start inhibitors:

Hood has been opened
Driver seatbelt is disengaged (this is an automatic start inhibitor therefore the engine can be restarted by depressing the clutch pedal)
Driver door is unlatched (this is an automatic start inhibitor therefore the engine can be restarted by depressing the clutch pedal).

Vehicle system inhibitor:

There is a system fault.

Auto Stop/Start Starter Motor Strategy

Engine restart without starter motor intervention

When the PCM detects engine restart parameters resulting from a driver action or system request, the PCM activates the fuel injection and ignition systems to allow the engine to continue to operate. This is available at a variable engine speed threshold which depends on engine type.

Engine restart with starter motor intervention

If the PCM cannot restart the engine without intervention, the restarting of the engine is controlled via the starter motor. The starter motor has the capability of engaging with the transmission ring gear whilst still rotating.

If an engine restart is initiated, the PCM activates the starter motor via the starter relay at the earliest opportunity to rotate the engine, then on the first available compression the PCM operates the fuel injection and ignition systems to restart the engine in less than 0.36 sec.