Quote:
Originally Posted by Just call me Sean
Yes, it is OBDI. Reads the same up to '95.
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ALDL (Assembly Line Diagnostic Link) and OBD I are not the same thing.
ALDL was the GM proprietary 160baud and 8291baud datalink on the computer equipped 1982-1995 GM vehicles. In North America GM used a 12 terminal Metripak 280 jack. GM Holden and Opel divisions used a different jack. Notice that they modified the data timing (160 baud rather than 300 and 8291 rather than 9600) so you couldn't simply use a Maxwell level shifter and talk to it with a standard Rockwell RS232 port. It takes a bit more ingenuity to plug the ALDL ECMs into a PC.
GM suffered from the same division rivalry that killed British Leyland. ALDL had a lot in common with the workers milling around after the curse at the Tower of Babel. Vehicles in the same nameplate using engines and controllers from other divisions spoke a slightly different dialect or completely different language from others. It must've been a special kind of nightmare for the EEs at Bosch, or Vetronix, or HP to build and program the Tech 1.
Pre-OBD II Ford/Lincoln/Mercury EEC I-IV vehicles were the same kind of nightmare. Chrysler was a similar mess. The other car manufacturers were similar. VW, Audi, Porsche, BMW, Benz, Vauxall, ... the list goes on.
OBD I is not an SAE or ISO or IEC or ... standard. California passed legislation requiring 1991 and later California Emissions Certified vehicles provide specific onboard diagnostic information in a specific format to CARB (California Air Resources Board) emissions testing stations. This was called OBD I. Outside of California emissions equipped vehicles OBD I did not exist and prior to the 1991 model year OBD I did not exist in California.
There were some bastard not-quite OBD II and not quite older spec orphans for the 1995 model year. Every manufacturer had them.
The US Federal government, Canada, and European OBD II specs superseded the CARB OBD I standards starting in the 1996 model year.