Clutch switch is connected to clutch pedal and transmits clutch operating state to ECM.

When clutch pedal is depressed during driving, engine load changes from loaded to none loaded condition. However, ECM regards vehicle to be loaded becuase VSS signal is still inputted to it. therefore, ECM controls none loaded engine with the condition suitable for loaded engine.

Accordingly, optimum fuel injection control is not performed then, RPM becomes unstable and smoke is produced.

Clutch operation is detected through clutch switch signal. This signal enables ECM to cope with instant change of load condition.

Besides, clutch switch signal is used to detect engaged gear with vehicle speed and engine speed.