Without Scan Tool

On OBD 1 diagnostic trouble codes may be obtained by recording Malfunction Indicator Lamp (MIL) flash codes. Terminal B of the DLC is the diagnostic terminal and is grounded by connecting it to terminal A (internal ECM/PCM ground). Once terminals A and B have been connected, the ignition switch must be moved to the On position with the engine not running. The Service Engine Soon light should flash Diagnostic Trouble Code (DTC) 12 three times consecutively. The flash sequence should be as follows: flash, pause, flash-flash, long pause, flash, pause, flash-flash, long pause, flash, pause, flash-flash. DTC 12 indicates that the system is operating properly. If DTC 12 is not indicated, a problem is present within the diagnostic system itself.

Following the output of DTC 12, the Service Engine Soon light will indicate a diagnostic trouble code three times, if present, or it will continue to output DTC 12. If more than one code is present, the codes will be output in lowest number to highest with each code being output three times.