commanded gear indicator for 4L80E w/ standalone TCM

[Dullahan]

I'd like to make a commanded gear indicator for a truck without a standard ECM/PCM. It's a 6.5 Diesel with a DB2/4L80E, and a standalone TCM. Thanks to this post - https://www.thetruckstop.us/forum/threads/4l80e-shift-indicator-lights.34643/ I think I could rig something up by tapping the shift solenoid wires. BTW, the shift table in that post is for a 4L60, not a 4L80.

But is there a better, easier to install, more portable way to do the same thing? Is the commanded gear and TCC lockup status available from the ALDL? What's the communication protocol for the TCM - is it basically OBD 1, OBD 2, or ??? I tried connecting to it with AutoEnginuity, no luck there. I don't have the TCM in front of me, but I think it's part #16196390

 

[THEFERMANATOR]

If you're using a GM stand alone TCM, then it's OBD1, so you're on your own building something to display the current gear. You could tap into the harness from the trans into the pressure switch manifold outputs to observe the position of the shift valves, but you would have to be VERY carefull to use diodes and transistors as any feedback could cause issues with the TCM. If all you want is to know the position of the shifter, then you could rig up a NSBU switch, but that would require a shift shaft change and a custom shift cable.

 

[Dullahan]

Thanks, it's good to know I'm dealing with OBD1. Yeah, it's a GM TCM. I can get software for a microcontroller to read OBD2, but I might have to start from scratch for OBD1. If I go the shift solenoid route, I'm planning on using opto couplers on the inputs to completely isolate the TCM circuits from the controller board. But getting the info from the ALDL would be better, assuming it's there to get. Any good OBD1 references out there?

 

[THEFERMANATOR]

I know there's alot of info on how to scan them vua tuner pro. You have to either buy or assemble your gateway to access the system, then tuner pro provides an open source software you can then program to read it. Once you know what you're looking for, you could possibly build something to read it that way. With the shift solenoids you have to remember its 4 gears and only 2 solenoids, so its a combo of the 2 for which gear. The psm has switches in it that detect which hydraulic circuit is commanded, but again, some might be combinations.

 

[Dullahan]

I saw some stuff about tuner pro when I was searching, but missed that it's open source. That's cool! And here's the info for the shift solenoid setup in case anyone finds it useful