On-Board Diagnostic System

ON-BOARD DIAGNOSTICS
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 a malfunction has continued for a specified time or longer since the irregular signal is initially monitored, the engine control module judges that a malfunction has occurred.
After the engine control module first detects a malfunction, a diagnostic trouble code is recorded when the engine is restarted and the same malfunction is re-detected. However, for items marked with a "*," a diagnostic trouble code is recorded on the first detection of the malfunction.
There are 42 diagnostic items, and the diagnostic results can be read out with a 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, the diagnostic trouble code can also be erased by turning the ignition switch to ON 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 to the engine control module in order to erase the diagnostic memory.
- The diagnostic trouble code of ignition timing adjustment signal is output whenever terminal for ignition timing adjustment is grounded. Therefore, it is not a malfunction that the code is output when adjusting ignition timing.

The 42 diagnostic items are provided as follows, and if plural items are activated, they are all indicated sequentially from the smallest code number.

The engine control module records the diagnostic trouble code and the engine operating conditions at the time the malfunction was detected. These data are called "freeze frame" data.
This data indicates the engine operating condition from when nothing at all is detected to the initial detection of malfunction.
This data can be read by using the scan tool, and can then be used in simulation tests for troubleshooting. Data items are listed in the image.

The Electronic Control Module carries out activities such as fuel injection control, idle air control and ignition timing control. In addition, the Electronic Control Module is equipped with several diagnostic test modes which simplify troubleshooting when a problem develops.

When an abnormality is detected in one of the sensors or actuators related to emission control, the CHECK ENGINE/MALFUNCTION INDICATOR LAMP illuminates as a warning to the driver.

When an abnormality is detected in one of the sensors or actuators, a diagnostic trouble code corresponding to the abnormality is output.

The RAM data inside the Electronic Control Module that is related to the sensors and actuators can be read by means of the scan tool or by reading the MIL blinks. In addition, the actuators can be controlled under certain circumstances.