System Operation

DIAGNOSTIC CHART (FAULT TREE)

ON-BOARD DIAGNOSTIC
The engine control module monitors the input/output signals (some signals at all times and the others under specified conditions) of the engine control module.
When it is noticed that an irregularity has continued for a specified time or longer from when the irregular signal is initially monitored, passing a certain number, the engine control module judges that an irregularity has occurred, memorizes the diagnostic trouble code, and outputs the signal to the on-board diagnostic output terminal.
There are 15 on-board diagnostic items including the normal state, and the diagnostic results can be read out with a voltmeter or scan tool.
Moreover, since memorization of the diagnostic trouble codes is backed up directly by the battery, the diagnostic results are memorized even if the ignition key is turned off. The diagnostic trouble codes will, however, be erased when the battery terminal or the engine control module connector is disconnected. In addition, beginning with the engine control module of 1990 and later models, the diagnostic trouble codes are erased by turning on the ignition switch and sending the diagnostic trouble code erase signal from the scan tool to the engine control module.

CAUTION: If the sensor connector is disconnected with the ignition switch turned on, the diagnostic trouble code is memorized. In this case, send the diagnostic trouble code erase signal from the scan tool to the engine control module or disconnect the battery terminal (-) for 10 seconds or more, and the diagnostic memory will be erased.

The 15 on-board diagnostic items are provided in the table above, and if plural items are activated, they are all indicated sequentially from the smallest code number.