Description of On-Board Diagnostics

Operation
When troubles occur in the main input devices or output devices of the engine control system, they are recorded in the memory of the ECM.
Failures of each input and output device are indicated and retrieved from the ECM as diagnostic trouble code (DTC) numbers.

NOTE: For input devices, the ECM continuously checks for malfunctions. For output devices, it checks for malfunctions only in a three-second period after the ignition switch is turned to ON, or the "TEN" terminal in the data link connector is grounded.






DTC Retrieval
DTCs can be retrieved from ECM memory by using the special service tools (SST) shown in the accompanying image.
For more information on DTC retrieval see: How to Display and Read Diagnostic Trouble Codes.