Sorry for not posting an update. I grabbed a scan tool and took my boss for a ride. The pcm is telling the trans to shift into 2nd, nothing happens. When it shows 3rd, it makes the shift, INTO 3RD. Doesn't have second at all. I must have been counting the shifts incorrectly, OD and lock up. If I cancel OD with the button on the shifter, I have 1st, 3rd and D. Sounds more like the mechanical diode. I don't have to tools or time to rebuild it myself. I priced a couple local transmission shops for overhaul, bench job, I R&R. Price was a little cheaper but only a 1 year warranty, at their shop and I remove if there is a problem. Decided to just install a Jasper unit. 3 year nation wide warranty and they pay to remove. Installed yesterday and everything is good again, except for the wallet.

 

The transmission is a four speed. 1,2,3, and 4. When you cancel OD you have 1,2, and 3. D is not a gear, that's a location for the shift handle. What you probably had was 1,3, and torque converter lockup.

 

Good to hear you have it diagnosed. My earlier posts were a method to tell if it was doing a 1-2 (stuck 1-2 accum) or 1-3 (bad mech diode) shift without a scan tool. Shorting SS2 to GND at low mph speeds will put it in 2nd via the valve body. No 2nd = bad mech diode likely.

Doing it with a scan tool is easier as you have found out. It sounds like it is is doing a 1-3 shift and a 1-3-TCC_lock shift with OD off.

Overall, I would declare the mechanical diode at fault. Thank you for posting the update.