Idle Stop & Go (ISG) function automatically switches off the engine when the car is at a standstill and the clutch is not operated and starts it again as soon as the clutch is operated. This not only reduces fuel consumption, but also lowers emissions. Idle Stop & Go (ISG) function also has a built-in sensitivity for driving safety and comfort.
The ISG system will not operate in certain conditions for example, when the engine coolant is still cold, when the battery is running low, or when the outside temperature is below 2℃. Also, it can be deactivated by pressing the ISG OFF switch on the crashpad lower panel.
Sample scenario: switching off the engine at a standstill at a red traffic light or in stop-and-go traffic.
Vehicle is moving.
Gear is engaged. The accelerator pedal is pressed.
The engine is running.
The driver brakes until the vehicle comes to a standstill.
The driver engages neutral and releases the clutch pedal.
The engine stops. The symbol "AUTO STOP" lights up in the instrument cluster.
The driver wants to continue the journey.
The driver presses the clutch pedal. The engine starts.
The gear can be engaged and the journey is continued. The symbol "AUTO STOP" goes out.
The battery sensor perceives battery status. Battery status is a major influencing factor on the ISG function. Its purpose is to ensure reliable start of the combustion engine after a defined parking period from the perspective of the vehicle energy system.
The Battery sensor monitors the following data:
Battery charge condition
Battery temperature
Voltage dip on engine start
In order to ensure adequate brake power assistance in every situation, the brake booster is equipped with a partial vacuum sensor. The brake booster vacuum pressure sensor is located beside the brake booster.
With an excessively low brake particl vacuum, the ISG function is activated without activity on the part of the driver. Insufficient brake partial vacuum can lead to safety risks during braking manoeuvres when rolling on an inclination. To prevent this, the engine will be started.
In all cases, the ISG function comes with the intelligent alternator control. The much more frequent charge and discharge cycles mean that the load on the battery is very high. The cycle resistance of AGM batteries means that they achieve similar results with regard to service life despite the high load.
Ensure that an AGM battery is fitted.
In all cases, an AGM battery must be installed and registered in the vehicle for the ISG function to work perfectly.
Due to the considerably more frequent occurrence of starting operations, the electrical load that occurs often leads to voltage dips in the vehicle network. In order to stabilize the power supply for certain voltage-sensitive electrical components, a DC/DC converter is used in conjunction with the ISG function.
The DC/DC converter supplies the relay with a voltage that also remains constant during the starting operation.
The DC/DC converter is fitted at the behind of the glove box.
Via the test leads for input voltage and the start relay , the electronics decide whether the power is supplied to the output via the bypass or the DC/DC converter.
In the bypass mode, the on-board supply voltage is not fed across the DC/DC converter and rather is transferred directly to the outputs. In the booster phase, the vehicle voltage is adapted.
The ISG OFF switch on the crashpad lower panel can be used to deactivate the ISG function.
The battery discharge during the engine shutdown by the ISG function means that a more powerful alternator is installed.
In conjunction with the ISG function, the starter motor must perform a great deal more work. The starter motor is therefore configured for a significantly higher number of start cycles. The components of the starter motor have been adapted to the higher requirements.
The neutral switch is mounted on top of the transmission case.
The neutral switch detects the idle position of the gearstick.
The present clutch switch is used as an input variable for the ISG function to detect clutch operation.
Via the seat belt/Door switch, the ISG function can detect if the driver has fastened the seat belt/closed the door. If the driver has not fastened the seat belt/closed the door, the ISG function will react as follows. If the seat belt is not fastened or door is open, the engine will not start or stop by the ISG function for safety reasons.
The hood switch is one of the influencing factors of determining the activation of ISG function. If the hood is open, the engine will not start or stop by the ISG function for safety reasons.
The ISG system is strongly networked with the power management. In the event of battery replacement, disconnection of the battery terminal or after changing the engine management system, the reference data regarding the battery charge state and battery condition can be lost.
They are only available again a closed-circuit current measurement of approximate 4 hours in which the vehicle may not be wakened. In this time, the ISG system is inactive.
After every engine start, the function is automatically becomes active and on stand-by. The ISG OFF switch can be used to deactivate the function manually until the next terminal change. The indication lamp lights up to confirm pressing of the switch.
Conditions Required |
The engine coolant temperature is not too low (Over 45 degree). |
No DPF regeneration |
No inhibitor condition for operating strategy or engine fault - CKPS, CMPS, ECTS, VSS, Battery sensor, BBVPS, Neutral Switch, Clutch Switch, APS, Injector |
Battery charge status is adequately high. |
No communication line error - LIN, CAN |
Vehicle speed is below 5 km/h |
Vehicle speed is over 10 km/h at least once after key start or idle start |
ISG OFF switch off |
Driver side seat belt, driver side door and hood are closed. |
Battery temperature is 2 - 55℃. |
Brake booster pressure is not too low. |
Blower not maximum |
Conditions Required |
Inhibitor condition for operating strategy not satisfied or engine fault - CKPS, CMPS, ECTS, VSS, Battery sensor, Neutral Switch, Clutch Switch, APS |
No communication line error - LIN, CAN |
Driver side seat belt, driver side door and hood are closed. |
Engine stalled, gear position was switched from engaged to neutral and clutch pedal was pressed. |
In case of error in idle stop status, the engine can be started by the key only.
The engine will start automatically without the driver's action if any of the following occurs:
Conditions Required |
Inhibitor condition for operating strategy not satisfied - TPS, CKPS, CMPS, ECTS, VSS, Battery sensor, BBVPS, Neutral Switch, Clutch Switch |
Brake booster vacuum pressure is low. |
When the battery charge status is low. |
A certain amount of time has passed after the air conditioning is On. |
Vehicle speed is over 5 km/h on a downward inclination. |
Blower maximum |
ISG system deactivated by fault
Faulty communication line (LIN/CAN)
Faulty neutral switch
Faulty brake booster vacuum pressure sensor
Faulty clutch switch
When the ISG related sensors or system error occurs, the ISG OFF switch lights up.
Especially, when the battery sensor has been replaced or reinstalled, the vehicle must be placed in ignition OFF for about 4 hours for recalibration.
The ISG function will operate normally after 4 hours.
When the engine is in Idle stop mode, it's possible to restart the engine without the driver taking any action.
Before leaving the car or doing anything in the engine room area, stop the engine by turning the ignition key to the LOCK position or removing it.