According to the 97 manual with a 5VZ-FE the ecm sends voltage from pin 27 (SL) of the ecm plug to the solenoid in the transmission to turn it on. If you pull that plug off the ecm and measure that wire to ground the spec says 11 to 15 ohms thru the solenoid coil. IF that tests good, "replace the ecm" There are 4 plugs into the ECM. This plug is the first on the left and the pin is the bottom most right, the 4th horizontal row down. If it doen't check good could be the connector on the transmission flakey. It shows that on pin 3 of the plug into the xmission. Is your converter going into lockup over 50MPH OK. That is what this controls.It is supposed to set the code if the resistance through the solenoid is more than 100K ohms or less than 8 ohms.