No Scan Data / Won't Flash DTC 12

Chart IV.:

PCM Wiring:

DESCRIPTION
There should always be a steady SERVICE ENGINE SOON 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 Code 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 Code 12.
^ If Code 12 does flash, make sure Scan Tool will work properly on another vehicle.
^ A steady light suggests a short to ground in the lamp control Circuit 419, or an open in diagnostic Circuit 451.
^ Check the tightness of the female terminals with a spare male terminal.