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, it also lowers emissions.Idle Stop & Go (ISG) function also has a built-in sensitivity to driving safety and comfort.
The engine is not switched off if certain conditions relating to safety and comfort have not been fulfilled (For example, when the engine coolant is still cold, when the battery is running low or when the outside temperature is below 2℃). 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 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 continued. The symbol "AUTO STOP" goes out.
The battery sensor perceives battery status. Battery status is a major influencing factor on the ISG function. The aim is to enable a 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 a brake partial vacuum that is too low, the ISG fuction also starts without activity on the part of the driver.Insufficient brake partial vacuum can lead to safety risks during braking manoeuvres, when rolling on an incline. To prevent this, the engine is 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 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, 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 do 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 that the driver has fastened the seat belt/door. If the driver has not fastened the seat belt/door, the ISG function reacts as follows. If the seat belt or door is opened, the engine must not be started or stopped by the ISG function for safety reasons.
The hood switch is included as the influencing factors in the calculation of the ISG function. If the hood is open, the engine must not be started or stopped 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 active and on stand-by. The ISG OFF switch can be used to deactivate the function manually until the next terminal change. Pressing the switch is confirmed by an lamp lighting up.
Conditions Required |
The engine coolant temperature is not too low (Over 45 degree). |
Not DPF regeneration |
Not 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. |
Not communication line error - LIN, CAN |
Vehicle speed less than 5kph |
Vehicle speed over 10kph at least once after key starting or idle starting |
ISG OFF switch off |
Driver’s seat belt and Driver’s Door and hood are closed. |
Battery temperature is between 2 to 55 degree. |
Brake booster pressure not to low. |
Not Blower max. |
Conditions Required |
Not inhibitor condition for operating strategy or engine fault - CKPS, CMPS, ECTS, VSS, Battery sensor, Neutral Switch, Clutch Switch, APS |
Not communication line error - LIN, CAN |
Driver’s seat belt and Driver’s Door or hood are closed. |
Engine stalled, then changed gear position (engaged → neutral) and pressed clutch pedal. |
If error occurred in the idle stop status, it is possible to start the engine by the key only.
The engine will start automatically without the driver's action if any of the following occurs:
Conditions Required |
Not inhibitor condition for operating strategy - 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 5kph by rolling down a hill. |
Blower Max. |
ISG system deactivation by fault
Fault in communication line (LIN/CAN)
Fault neutral switch
Fault brake booster vacuum pressure sensor
Fault clutch switch
When the ISG related sensors or system error occurs, the ISG OFF switch lights up.
Especially when the battery sensor is replaced or reinstalled, the vehicle must be placed in the ignition switch OFF for about 4 hours for recalibration.
The ISG function is operated about 4 hours later normally.
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.
