Description of On-Board Diagnostics

PURPOSE
The engine control module contains a built-in self diagnostic system by which malfunctions within the engine signal network are detected. By analyzing various signals, the engine control module can detect a malfunction and a diagnostic trouble code is stored in its memory for help with diagnosis. At the same time the malfunction indicator lamp on the combination meter lights up to indicate the engine control module has detected a malfunction and stored the diagnostic trouble code.

OPERATION

Self Diagnosis
The engine control module monitors the input/output signals (some signals at all times and others under specified conditions). When the engine control module detects that an irregularity exists it memorizes the diagnostic trouble code, and outputs the signal to the self diagnosis output terminal. There are 15 diagnosis items, including the normal state, and the diagnosis results can be read out with a voltmeter or scan tool. Diagnostic trouble codes will remain in the engine control module as long as battery power is maintained. The diagnostic trouble codes will, however, be erased when the battery terminal or engine control module connector is disconnected.

Malfunction Indicator Light
If a component or system malfunction is detected, the engine control module will illuminate the malfunction indicator light and record the corresponding diagnostic trouble code or codes in memory. However, when the engine control module judges that the component or system has returned to normal, the engine control module will turn off the malfunction indicator lamp. If the ignition switch is turned OFF and then ON again, the engine control module will not illuminate the malfunction indicator lamp until the irregularity is detected again.
Under normal operating conditions, the malfunction indicator lamp will be lit for 5 seconds immediately after the engine is started. This is to indicate that the light is not burned out.

NOTE: When the ignition timing adjustment terminal is shorted to ground during ignition timing inspection/adjustment procedures, the engine control module will store a Fault Code 36 in memory and illuminate the malfunction indicator lamp.