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ALDL 12 pins connector - front view. Assembly Line Diagnostic Link, Assembly Line Data Link, or ALDL is a proprietary on-board diagnostics system developed by General Motors before the standardization of OBD-2.
Some software applications that allow interfacing to GMLAN are Intrepid Control Systems, Inc.'s Vehicle Spy 3; Vector's CANoe; Dearborn Group's Hercules, ETAS' ES-1222, ES590, ES715, and ES580; ScanTool.net's OBDLink MX; EControls by Enovation Controls' CANCapture; and GMLAN vehicle universal remote control GMRC for Android devices
(GM did not use the term OBD 1.5 in the documentation for these vehicles — they simply have an OBD and an OBD-II section in the service manual.) For example, the 1994–1995 model year Corvettes have one post-catalyst oxygen sensor (although they have two catalytic converters), and have a subset of the OBD-II codes implemented. [20]
Also, prior to 1996, there was no standardization for these connectors, and each manufacturer had its own shape with a unique pin arrangement. After 1996, many manufacturers retained their proprietary connectors in addition to the OBD-II interface, because OBD-II ports are only required to transmit emission-related codes and data. [2]
The complete configuration of a GM vehicle (as it exited the factory) can be described by specifying the base model and a complete list of its RPO codes. [1] Some dealerships are willing to run a VIN and print out its RPOs (with their definitions) free of charge. The records are in GMs' electronic database since at least the 1990 models.
Society of Automotive Engineers standard SAE J1939 is the vehicle bus recommended practice used for communication and diagnostics among vehicle components. Originating in the car and heavy-duty truck industry in the United States, it is now widely used in other parts of the world.
OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a subset of these codes, primarily for state mandated emissions inspections .
When the MIL is lit, the engine control unit stores a fault code related to the malfunction, which can be retrieved—although in many models this requires the use of a scan tool. This warning light can indicate almost anything from a loose gas cap to a serious knock or fault in the engine. [4]