With Manufacturer's Scan Tool

Data Link Connector And Junction Block:

READING CODES WITH THE TECH 1 SCANNER (or equivalent)
The provisions for communicating with the Electronic Control Module (ECM) are the Assembly Line Diagnostic Link (ALDL) connector, the "DIAG SW" connector in the junction block and the "DIAGNOSTIC REQUEST TERMINAL" in the duty check coupler. The ALDL connector is located under the instrument panel to the left of the steering column. Codes stored in ECM memory can be read through the TECH 1 diagnostic computer/scanner (or equivalent) plugged into the ALDL connector. Follow all computer/scanner manufactures instructions.