ALDL

Assembly Line Diagnostic Link or ALDL was a proprietary on-board diagnostics system developed by General Motors prior to the standardization of OBD-2. For the assembly plant test system computer which was connected to this vehicle connector and known by the same name see the article IBM Series/1.

ALDL was previously called Assembly Line Communications Link or ALCL. The two terms are used synonymously.

This system was only vaguely standardized and suffered from the fact that specifications for the communications link varied from one model to the next. ALDL was largely used by manufacturers for diagnostics at their dealerships and official maintenance facilities. The connector is usually located under the dash on the driver's side of left-hand drive (LHD) vehicles, though this location was not standardized.

Diagnostic Connector

There were at least four different connectors used with ALDL. General Motors implemented both a 5-pin connector and a 12-pin connector, with the 12 pin connector (Packard/Delco/Delphi part number 12020043) being used in the vast majority of GM cars. Lotus implemented a 10-pin connector. The pins are given letter designations in the following layouts (as seen from the front of the vehicle connector):