Vehicle Bus - Early History of Buses On GM Vehicles

Early History of Buses On GM Vehicles

The earliest known GM data communication link from one electronic module to another was introduced in the 1980 model year Cadillacs. The link was one wire point to point, linking the engine control module to the fuel data panel. In model year 1981 all GM passenger cars for the US market used a similar data link to a test connector for assembly line diagnostics. The value of this data in diagnosing emission systems after customer delivery was quickly identified. Scanner tools were made to view and interpret the data stream. The data line was the same line that turned on the "Check Engine" lamp in the instrument panel. Data was sent at 80 bits per sec. 9 bits per frame, 21 bytes (frames), 2.4 sec./transmission.

In 1981 model year Cadillacs, two 80 bit point to point links were present, with the second link going from the engine control module to the climate control module.

In the 1982 model year, fuel injection engine control modules had the data port moved to a dedicated full-time connection (Corvette and 2.5 L engines).

In the 1983 model year, the data rate on the fuel injection engine control modules was doubled to 160 bit/s.

In the 1984 model year, Corvette Instrument panel used data from the fuel injection engine control module's data link.

In the 1985 model year, Cadillac FWD "C" vehicle had an electronic system that had point to point data links between 5 electronic modules and a dedicated assembly line diagnostic connector.

On the 1988 and 1989 model year Buick Reatta and 1986–1989 model year Buick Riviera touchscreen CRT equipped vehicles, an 8,192 bit/s data bus was implemented between the body computer module and the assembly line connector, climate control module, and CRT controller. This was GM's first multi-drop data bus. All GM vehicles adopted this bus as new engine control modules were developed. This bus remained the standard GM vehicle bus until 1996 when the J1850 VPW bus replaced it.