[Sean486]

Originally Posted by Dispatch20

Quick update; sorry about all the text and no fun pictures!

I wired a ground wire from the ECU harness pin 17 direct to a ground pin on the Arduino. I think this might have actually helped! I took two long drives today (separated by 11 hours) and did not get a pending P1702 or CEL. I noticed that wiring this ground also made my datalogging Arduino setup work better. I want to test for a few more days before I claim success, though, but I'm feeling pretty good about it now.

I also datalogged and disconnected the large transmission harness by the starter to see what would happen. When you disconnect the big connector, the TCU just sends all '1's to the ECU which guarantees the P1702 will go on. The TCU must fail to see the right loads/solenoids/switches in the transmission and send the alert to the ECU via the pin 80 "diagnosis" signal. This lends credence to the theory that adding load resistors to the TCU could fool it into thinking it has a proper automatic installed despite having a 5MT swap.

Strangely, after filling up gas on the second half of my 2nd test drive today I got a pending 1101 Neutral Safety switch code. It seems unrelated to this testing but maybe some dirt got in the tranny harness when I plugged it back together, or maybe I didn't plug it all the way in. I'll keep an eye on that.

Lastly, the TCU does, in fact, start sending the serial data when the key enters the ON position (not Accessory). My Arduino starts sending data to the ECU when Accessory power comes on but it doesn't seem to matter. I also noticed that the power cuts out to Accessory devices when the starter is engaged, but it does NOT cut to the TCU. This doesn't seem to matter in terms of P1702, either.

Wow! This is awesome news. Hopefully, it doesn't come back.