Engine Stop Start
How does Engine Stop Start (ESS) system function - simple overview:
- Powertrain Control Module (PCM) calibration makes the decision when to shut off the engine and when to restart the engine again
- The ESS shuts the engine off when the vehicle stops. The vehicle has to be stopped for a pre-set time before the engine is switched off.
- When the engine stops, a 12-volt auxiliary battery keeps accessory features powered, like the fan, wipers, headlights, audio system, etc.
- Then, ESS system autostarts when the driver releases the brake pedal allowing the vehicle to move. An in-rush current relay (ICR) is used to smooth out voltage dips when the starter cranks the engine.
Primary Autostop Enablers - Brake pedal depressed (automatic transmission).
Secondary Autostop Enablers - Vehicle speed, coolant temperature, hood closed, doors closed, driver's seat belt latched, interior climate and settings, battery state and energy demand, steering wheel angle, steering wheel torque, ambient temperature, time and speed since last autostop, transfer case position, and ESC status, No stop-start related faults present.
Autostop Events
- Autostop state broadcast on Controller Area Network (CAN) bus.
- Instrument Panel Cluster (IPC) telltales illuminate.
- Engine shutdown begins.
As the engine slows it passes through three phases:
- Fuel and spark restart permissible.
- Restart prohibited.
- Restart permitted, based on start system employed.
Autostart requests are evaluated throughout the autostop event.
When in autostop:
- IPC ESS telltale remains illuminated.
- IPC displays the autostop state message.
- Body Control Module (BCM) starter relay driver is then energized providing the PCM with direct starter control.
Vehicle Function:
- Consumer electronics continue to function in a normal manner.
- Heating, Ventilation, Air Conditioning (HVAC) fan speed and other setting adjusted to maximize cabin comfort and autostop duration (based on climate control settings and conditions).
- Electric Power Steering (EPS) maintained during autostop, possibly with reduced maximum assist.
System Requested Autostarts:
- Battery State.
- Brake Vacuum.
- Climate control stress.
- Vehicle speed.
- Steering wheel angle or torque.
- Transmission selector position.
Stop-Start Disable (while autostopped)
- Vehicle systems monitored that may disable stop-start (requiring a key restart if in autostop) include: hood opened, occupant sensing indicating driver not present, unsafe gear shift position for autostart and critical system faults.
Autostart Decision:
- All autostart enablers present.
- Brake pedal released or shifter place in reverse (automatic transmissions).
- Clutch pedal depressed past the up-stop position (manual transmission).
- Throttle pedal depressed.
Autostart Events:
- Autostart state broadcasted on the CAN bus.
- IPC ESS telltale illumination cancelled.
- IPC message changed to previous IPC message (outside temp and compass, etc).
- Voltage Stability Modules (VSM)'s are placed in voltage conditioning mode.
- Hill Start Assist (HSA) requested.
- Starter relay commanded to initiate cranking.
- Engine achieves idle speed.
Launch Events:
- Automatic transmission clutches engaged.
- HSA released.
- HVAC control returned to pre-autostop conditions.
- ESS state (ready) broadcasted on the CAN bus.
- Embedded IPC ESS message indicating "Stop/Start Ready" displays.
| Planned Autostart (Engine On) Enable Conditions: |
|---|
| 1. Valid target gear and brake switch pressure condition. |
| 2. Completed initial engine key start. |
| 3. Occupant sensing allow engine start condition met. |
| 4. On Board Diagnostics (OBD) allow engine start condition met. |
| 5. Vehicle hood not Ajar. |
| Potential Autostop (Engine Off) Enable Conditions: |
|---|
| 1. Tow haul mode not active. |
| 2. Steering wheel angle within defined range. |
| 3. Steering wheel angle gradient within defined range. |
| 4. Steering column torque within defined range. |
| 5. Battery health state of function greater than threshold. |
| Planned Autostop (Engine Off) Enable Conditions: |
|---|
| 1. Valid target gear and brake switch pressure state combination. |
| 2. Threshold vehicle speed exceeded or timed-out since last shift out of reverse. |
| 3. Transmission ready. |
| 4. 4WD Low mode not active. |
| 5. Starter cool down condition met after reaching max allowable consecutive restarts. |
| 6. Ambient temperature within defined range. |
| 7. Engine coolant temperature within defined range. |
| 8. Catalyst temperature within defined range. |
| 9. Battery temperature within defined range. |
| 10. Barometric pressure greater than threshold. |
| 11. Brake booster delta pressure less than threshold. |
| 12. Fuel level greater than threshold. |
| 13. Vehicle hood not Ajar. |
| 14. No throttle request. |
| 15. No engine stop inhibit request by HVAC. |
| 16. Battery state of charge greater than threshold. |
| 17. Battery voltage state of function greater than threshold. |
| 18. Engine speed less than threshold. |
| 19. Vehicle speed less than threshold. |
| 20. Threshold vehicle speed exceeded since last engine start. |
| 21. Occupant sensing allow engine stop condition met. |
| 22. OBD allow engine stop condition met. |
| 23. Engine runtime greater than threshold. |
| 24. ESS "Off" switch not activated. |
| 25. Flex fuel learn mode not active. |
| 26. Antilock Braking system (ABS) brake event not present. |
IPC Pop Up Messages Displayed on the IPC
- IPC message states Stop/Start Autostop Active
- No Chime.
- Normal Use.
- Pop-up maintained for 5 seconds.
- Displays with green hard telltale.
Stop/Start To Restart Press
- Single Chime.
- Driver put gear shift in gear without using Clutch; customer needs to return to Neutral or fully depress clutch pedal.
- Pop up maintained for 5 seconds.
Stop/Start Restart Required Fault Detected
- Single Chime.
- Malfunction Indicator Lamp (MIL) or ESS system fault preventing safe state confirmation during autostop.
IPC Pop Up Messages Displayed within IPC "Ring" menu
Stop/Start Ready
- Stop-Start conditions met to enable engine stop.
Stop/Start Off
- Stop-Start turned off by the customer at the switch.
Stop/Start Not Ready
- Stop-Start conditions are not met to enable engine stop (ex: HVAC settings, engine temperature, etc).
Stop/Start Not Ready Steering Wheel Turned
- Stop-Start condition not met with steering wheel turned past calibrated angle.