The Idle Stop & Go (ISG) system turns off the ignition when the vehicle stops, and then restarts the ignition and starts the vehicle when the accelerator pedal is pressed. It temporarily stops the engine while waiting for a signal, or improves idle fuel economy and reduces exhaust emissions. However, the ISG system may not operate if the engine oil or ambient temperature is too low, or if the 12 V battery voltage is too low. The system can be deactivated by pressing the ISG OFF switch when the driver does not want to use the ISG system. Example scenario: engine stops while waiting at a red traffic light or in traffic jams.
The vehicle is moving.
Gear engaged. Accelerator pedal depressed.
Engine running.
Driver brakes until the vehicle comes to a complete stop.
The driver shifts into neutral and releases the clutch pedal.
The engine stops. The "AUTO STOP" symbol illuminates on the instrument cluster.
Driver wants to continue driving.
The driver depresses the clutch pedal. The engine starts.
The gear can be engaged and the journey continued. The "AUTO STOP" symbol goes off.
Battery Sensor. The battery sensor monitors the battery condition. The battery condition is the main factor affecting the ISG function. The objective is to ensure reliable engine restart after a certain period of standstill from the point of view of the vehicle's energy system. The battery sensor monitors the following data:
Battery Charge Status
Battery Temperature
Voltage Dip During Engine Starting
Brake Booster Vacuum Sensor. To ensure adequate braking assistance in any situation, the booster is equipped with a partial vacuum sensor. The brake booster vacuum sensor is located next to the brake booster.
AGM Battery. In all cases the ISG function is supplied with intelligent generator control. Much more frequent charging and discharging cycles mean that the load on the battery is very high. The cycle endurance of AGM batteries means that they achieve similar results in terms of service life despite the high load.
DC/DC Converter. Due to the significantly more frequent engine starts, the resulting electrical load often causes voltage dips in the vehicle power supply. To stabilize the power supply for some voltage-sensitive electrical components, a DC/DC converter is used in combination with the ISG function. The DC/DC converter supplies a constant voltage to the relay during the starting operation. The DC/DC converter is installed at the rear of the glove box. Using the sense wires for the input voltage and the starter relay, the electronics decide whether power is supplied to the output via the bypass or the DC/DC converter. In bypass mode, the vehicle system voltage is not supplied through the DC/DC converter; instead, it is transmitted directly to the outputs. In the booster phase, the vehicle voltage is adapted.ISG Switch. The ISG OFF switch on the lower part of the instrument panel can be used to deactivate the ISG function. Generator. Battery discharge while the engine is stopped by the ISG function means that a more powerful generator is installed.Starter Motor. In combination with the ISG function, the starter motor must perform considerably more work. Therefore, the starter motor is designed for a significantly higher number of starting cycles. The starter motor components have been adapted to the higher requirements.Neutral Switch. The neutral switch is installed on the upper part of the transmission case. The neutral switch detects the neutral position of the shift lever. Clutch Switch. The existing clutch switch is used as an input variable for the ISG function to determine clutch operation.Seat Belt/Door Switch (Driver). Using the seat belt/door switch, the ISG function can determine whether 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 responds as follows. If the seat belt or door is open, the engine cannot be started or stopped by the ISG function for safety reasons. Hood Switch. The hood switch is included as an influencing factor in the ISG function calculation. If the hood is open, the engine cannot be started or stopped by the ISG function for safety reasons.
Operating conditions for ISG function
After each engine start, the function is automatically activated and is in standby mode. The ISG OFF switch can be used to deactivate the function manually until the next ignition cycle. Pressing the switch is confirmed by the indicator lamp illuminating.
1. Idle stop condition (Idle → Stop)
▶ Normal condition: neutral position and clutch pedal released.
Required conditions
Engine coolant temperature is not too low (above 45 °C).
Not DPF regeneration
No inhibitor condition for operating strategy or engine malfunction
Driver seat belt and driver door or hood are closed.
Engine stalled, then gear selector moved (drive → neutral) and clutch pedal depressed.
3. Auto start condition (Stop → Start)
The engine will restart automatically without driver input if any of the following occurs: ▶ Normal condition: the transmission is in neutral and the clutch pedal is released.
