Description of On-Board Diagnostics

PURPOSE
The powertrain control module contains a built-in self diagnostic system by which malfunctions within the engine signal network are detected. By analyzing various signals, the powertrain 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 powertrain control module has detected a malfunction and stored the diagnostic trouble code.

OPERATION

Self Diagnosis
The powertrain control module monitors the input/output signals (some signals at all times and others under specified conditions). When the powertrain control module detects that an irregularity exists it memorizes the diagnostic trouble code, and outputs the signal to the self diagnosis output terminal.

Malfunction Indicator Light
If a component or system malfunction is detected, the powertrain control module will illuminate the malfunction indicator light and record the corresponding diagnostic trouble code or codes in memory. However, when the powertrain control module judges that the component or system has returned to normal, the powertrain control module will turn off the malfunction indicator lamp. If the ignition switch is turned OFF and then ON again, the powertrain 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.