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To extract a trouble from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.
To activate the Diagnostic mode, a special connector located in the center console is utilized. When the ALDL (assembly line diagnostic link) connector is jumpered between terminals "A" and "C" with the ignition "ON" and the engine not running, the light will flash any stored codes.
The ALDL diagnostic connector is located in the passenger compartment.