Operation

For ISC the ECM operates a "closed speed control loop" to maintain the target idle speed within 50 rpm.

Information is taken by the ECM regarding gear selection, intake temperature, and battery voltage to determine the required idle speed.

The park/neutral (rotary) switch provides gear selected information.

Should a low battery voltage be detected (= greater than 11.8 volts) the idle speed is increased by 50 rpm to increase generator output.

A change in engine load caused by services or functions can affect the idle speed significantly. In order that the idle speed be maintained within parameters, the ECM anticipates any impending change in load and adjusts the idle accordingly. This strategy is different to previous systems in that it is active rather than reactive. Load changes may be caused by;
- A/C compressor clutch
- Shifts from park/neutral to drive or reverse
- Lamps
- Heated windshield & backlight
- Engine cooling fans

The CAN bus relays information regarding the status of lamps and gear selection. Because the ECM directly controls compressor, screen heaters and cooling fans it is always "aware" of the system status.