Without Scan Tool

OPERATION:
To extract a trouble code from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.

ALDL Connector (Located Underdash):

The ALDL diagnostic connector is located in the passenger compartment. Terminal B of the connector is the test terminal and terminal A is the ground used for diagnostic display.

If the test terminal is grounded with the ignition "ON" and engine not running, the system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.