Without Scan Tool

Duty Check Data Link Connector (DLC):

PROCEDURE
The provisions for communicating with the Engine Control Module (ECM) are the Data Link Connector (DLC) and the diagnostic request terminal in the duty check DLC.

The duty check DLC is located in the right rear engine compartment near the battery. Diagnostic Trouble Codes (DTCs) stored in ECM memory can be read by counting the flashes of the malfunction indicator lamp (MIL) after grounding the diagnostic request terminal in the duty check DLC. When this terminal is grounded, the ECM enters its diagnostic mode and outputs DTCs to the Malfunction Indicator Lamp (MIL).

To ground the diagnostic request terminal in the duty check DLC, connect a jumper between duty check DLC cavities "2" and "3". At this point, the MIL should flash DTC 12 continuously. This would be the following flash sequence: "flash, pause, flash-flash, long pause, flash, pause, flash-flash, long pause, flash, pause, flash-flash," etc. DTC 12 indicates that the ECM's diagnostic system is operating. If DTC 12 is not indicated, a problem is present within the diagnostic system itself, refer to Diagnostic Charts / Chart A-1 No "Service Engine Soon" Light. Related Tests, Information and Procedures

If any DTCs exist indicating a problem (DTCs other than DTC 12), those DTCs will flash instead of a DTC 12. If more than one DTC is stored in the ECM's memory, the DTCs will be repeatedly output from the lowest to the highest, with each DTC being displayed three times.