With Manufacturer's Scan Tool

Assembly Line Diagnostic Link (ALDL) Connector (or DLC).:

READING DIAGNOSTIC TROUBLE CODES
The provision for communicating with the Engine Control Module (ECM) with a scan tool is the Data Link Connector (DLC). Diagnostic Trouble Codes (DTCs) stored in ECM memory can be read through the Tech 1 scan tool diagnostic computer (a hand-held diagnostic scanner) plugged into the DLC.

DATA LINK CONNECTOR
The DLC is located under the instrument panel to the left of the steering column and is initially used at the assembly plant for determining powerplant system integrity prior to vehicle shipment.