No Scan Data / Won't Flash DTC 12

Diagnostic Chart:

Diagnostic Chart (Cont'd):

Schematic Diagram:

CHART IV

NO SCAN TOOL DATA OR WON'T FLASH DTC 12
There should always be a steady malfunction indicator lamp when the ignition is On and engine stopped. Battery voltage is supplied directly to the lamp bulb. The powertrain control module (PCM) will control the lamp and turn it On by providing a ground path through circuit 419 to the PCM. With the diagnostic terminal grounded, the lamp should flash a DTC 12, followed by any trouble code(s) stored in memory.

DIAGNOSTIC AIDS
^ If there is a problem with the PCM that causes a Scan tool not to read serial data, the PCM should not flash a DTC 12.
^ If DTC 12 does flash, make sure Scan tool will work properly on another vehicle. If DTC 81 is flashed, refer to the diagnostic trouble code chart. Powertrain Controls - ECM/PCM
^ A steady light suggests a short to ground in the lamp control circuit 419, or an open in diagnostic circuit 448.
^ Check the tightness of the female terminals with a spare male terminal.