OBDII Mt conversion???

[Dispatch20]

I appreciate the support, guys! It does help motivate me knowing people are interested in this.

So after I posted last time, I set up the Arduino and laptop to do more data logging. I was suspecting that I might be missing some sort of TCU message that happens at highway speeds (or at some other period). Well, I did a 10 minute drive and the pattern did not change at all. It stayed exactly as I've always seen it. So then I cleared the CEL light, and drove another 10 minutes and there was no difference in the TCU pattern.

So anyways, I'm thinking that perhaps it is something simple like a grounding problem. The ECU has a number of different ground pins with different labels (refer to the OBD2 pinout link a few posts up). It would be very unsafe to assume all the different labeled grounds are all common with the chassis ground. So my next step is to wire the Arduino ground to the more specific ECU ground starting with the "control systems ground" on pins ECU 17/18). To be honest, I can just check with an ohmmeter to see how the grounds work, but I haven't yet. It's not the most convenient area (under the dash & steering wheel)