Description of On-Board Diagnostics

PURPOSE / OPERATION
The Engine Control Module monitors the input/output signals (some signals at all times and the others under specified conditions). When the Engine Control Module detects that an irregularity exists, it will commit a Diagnostic Trouble Code to memory and then output a signal to the Malfunction Indicator Lamp. There are 14 diagnosis items, including the normal state, and the diagnosis results can be read out with voltmeter or Scan Tool.
Trouble codes will remain in the Engine Control Module as long as battery power is maintained. The trouble codes will, however, be erased when the battery terminal or the Engine Control Module connector is disconnected.
If a sensor connector is disconnected with the ignition switch turned on, the Diagnostic Trouble Code is stored. In this case, disconnect the battery negative terminal (-) for 15 seconds or more, and the diagnosis memory will be erased.

NOTE: When battery voltage Is low, Diagnostic Trouble Codes can not be read. Be sure to check the battery for voltage and other conditions before starting the test.

NOTE: Diagnosis memory is erased if the battery or the Engine Control Module connector is disconnected. Do not disconnect the battery before the Diagnostic Trouble Codes are completely read.