Diagnostic Mode Switch/Connector: Description and Operation

ALDL Connector:

Scan Tool:
The ECM can output information to the underdash ALDL (Assembly Line Data Link) connector, allowing access to a variety of computer sensor circuit information. Information can be retrieved using several types of aftermarket scanners. Understanding the function of the circuit can be useful in obtaining information that might otherwise prove time consuming or impossible to obtain using other test procedures. Refer to manufacturers instructions for diagnostic test and code extraction.

Grounding Diagnostic Connector:
Ground the diagnostic test terminal with the engine not running and the ignition switch in the "ON" position. The "Malfunction Indicator Light" (MIL) will flash a Code 12 three times, and each code stored in memory three times. When all Codes have been displayed, a Code 12 will follow. New codes cannot be stored in the ECM once the diagnostics mode is activated until existing codes are cleared from memory. See DIAGNOSTIC CIRCUIT CHECK for a complete system check.