Thanks Andrew,This clears things up some. I actually lucked out. Turns out the 3.1 protocol is the same as the 3.4 - which is completely detailed in FreeScan. I'm still confused about the SumCheck part, however. Am I supposed to know the checksum of the stream before I get it? So I want to send it F4 57 01 64 what?
Bruce, Vin code is "H" for the 3.1. Thanks Jeremy
Remember this is "the chatter", and won't tell you much. The meat is whenyou request data from the ECM>You can pick apart packets from a datastream by looking for patterns andthen calculating the checksum. Use Win 95 Calculator, set to Hex and Byte mode. Add all digits, hit NOT, add 1. There's the checksum. Above, the 25 and 26 are RPM*25 values (925 and 950 RPM respectively), and the 40 is intake air temperature. When you send it a "shut up" command of F4 56 08 AE you can follow it up with a Mode Request, and that should start spitting real data at you. Thereare quite a few modes, they follow the format F4 57 01 XX CS, where XX is 00thru ??, and CS is checksum.
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