See Figure 1
The ECM contains a built-in, self-diagnosis system which detects troubles within the engine signal network. Once a malfunction is detected, the Malfunction Indicator Lamp (MIL), located on the instrument panel, will light.
By analyzing various signals, the ECM detects system malfunctions related to the operating sensors. The ECM stores the failure code associated with the detected failure until the diagnosis system is cleared.
The MIL on the instrument panel informs the driver that a malfunction has been detected. The light will go out automatically once the malfunction has been cleared.