With Manufacturer's Scan Tool

Diagnostic Circuit:

DIAGNOSTIC CIRCUIT CHECK:
Since this is the starting point for the diagnostic procedure or finding the cause of an emissions test failure, always begin here. The system check is performed through the twelve terminal Assembly Line Diagnostic Link (ALDL) connector under the instrument panel in the passenger compartment.

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

ALDL Or DLC Connector:

The ALDL diagnostic connector is located in the passenger compartment. A "Scan" tool can be connected to the ALDL connector to display codes and other diagnostic information, depending on which function the technician selects on the particular "Scan" tool being used.

FIELD SERVICE MODE:
A "Scan" tool can be used to enter the "Field Service Mode." When in this mode, the "Scan" tool is used to display data values from sensor inputs. These displayed values can then be compared to normal or "Typical" data values, to help isolate difficult to diagnose problems, or intermittents.

Scan Tool Note:
Not all SCAN testers are compatible with every system. A SCAN tool that produces faulty readings should NOT be used, and the problem should be reported to the tool manufacturer. Use of a faulty SCAN tool can result in improper diagnosis and unnecessary component replacement. Follow the proper instructions, located in the owners manual, for the specific SCAN tool being used.