Self-Diagnosis Function

ECM diagnoses troubles which may occur in the areas including the following parts when the ignition switch is ON or the engine is running, and indicates the result by turning on or flashing "CHECK ENGINE" light.

- Oxygen sensor
- Water temp. sensor
- Throttle position sensor
- Speed sensor
- Air flow sensor
- Ignition signal
- Crank angle sensor
- EGR system (California spec. model only)
- Fuel injector
- CPU (Central Processing Unit) of ECM

ECM and "CHECK ENGINE" light operate as follows.

"CHECK ENGINE" light lights when the ignition switch is turned ON (but the engine at stop) with the diagnosis switch terminal un-grounded regardless of the condition of electronic fuel injection system. This is only to check the "CHECK ENGINE" light bulb and its circuit.
- If the above areas of electronic fuel injection system is free from any trouble after the engine start (while engine is running), "CHECK ENGINE" light turns OFF.
- When ECM detects a trouble which has occurred in the above areas, it makes "CHECK ENGINE" light turn ON while the engine is running to warn the driver of such occurrence of trouble and at the same time it stores the exact trouble area in ECM back-up memory. (The memory is kept as it is even if the trouble was only temporary and disappeared immediately. And it is not erased unless the power to ECM is shut off for 30 seconds or longer.)

ECM also indicates trouble area in memory by means of flashing of "CHECK ENGINE" light at the time of inspection (i.e. when diagnosis switch terminal is grounded and ignition switch is turned ON).

NOTE: Only ignition circuit trouble (code No. 41 among the above areas is not stored in backup memory of ECM. (In other words, even if ECM has detected a trouble in ignition circuit, once ignition switch is turned OFF, code No. 41 will not be indicated even when diagnosis switch terminal is grounded and ignition switch is turned ON.).
Therefore, to check diagnostic code when engine fails to start, crank engine and then ground diagnostic switch terminal with ignition switch ON.