DESCRIPTION The ECU contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a "CHECK ENGINE" warning light on the instrument panel is illuminated. By analyzing various signals as shown in the later tables (See pages FI-26 to 28) the Electronic Control Unit (ECU) detects system malfunctions which are related to the various operating parameter sensors or to the actuator. The ECU stores the failure until the diagnosis system is cleared by removing the EFI fuse with the ignition switch off. A "CHECK ENGINE" warning light on the instrument panel informs the driver that a malfunction has been detected. The light goes out automatically when the malfunction has been cleared. "CHECK ENGINE" WARNING LIGHT CHECK 1. The "CHECK ENGINE" warning light will come on when the ignition switch is placed at ON and the engine is not running. 2. When the engine is started, the "CHECK ENGINE" warning light should go out. If the light remains on, the diagnosis system has detected a malfunction or abnormality in the system. OUTPUT OF DIAGNOSTIC CODES To obtain an output of diagnostic codes, proceed as follows: 1. Initial conditions (a) Battery voltage above 11 volts (b) Throttle valve fully closed (throttle position sensor IDL points closed) (c) Transmission in neutral position (d) Accessory switches OFF 2. Turn the ignition switch to ON. Do not start the engine. 3. Using SST, connect terminals TE1 and E1 of the check connector. SST 09843-18020 HINT: The check connector is located near the ignition coil.