Fault Detection and Trouble Code Memory Function

ON-BOARD DIAGNOSTICS
The Powertrain Control Module (PCM) monitors the input/output signals (some signals at all times and the others under specified conditions) of the PCM.

When a malfunction has continued for a specified time or longer since the irregular signal is initially monitored, the PCM judges that a malfunction has occurred.

After the PCM 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 60 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 PCM 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 PCM.

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 PCM in order to erase the diagnostic memory.
The 60 diagnostic items are all indicated sequentially from the smallest code number.

The PCM records the diagnostic trouble code and the engine operating conditions at the time the malfunction was detected. This data is 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 as follows.