oerdrive shift problem

[diggerrigger]

As the cold weather returned this year my '90 SR5 w/automatic OD tranny developed a problem shifting. An old thread by bilsif descibed the problem exactly. When the ambient temperature is cold, it takes too long before the shift to OD occurs. The colder it is the longer it takes. Some of the responses suggested that this was normal. It is not. It had never occurred in the past.
My analysis so far: A weak OD shift solinoid. I dissmissed this because it works perfectly once the first shift to OD is made. My current theory is that the ECM (or whatever else Toyota may call the computer) is blocking the shift due to receiving bad information from a sensor. The temperature guage on the dash responds normally.

Any ideas?

Does anyone have a source for Toyota ECM operation?

[diggerrigger]

any new blood out there who wants to take a shot at this?

[toyomoho]

You theory about the temp switch sounds good. In some Toyota cars such as Carmy, the O/D is locked out until the engine coolant temp rises. Your engine may have more then one coolant sensor. One for the temp gauge, one for the ECU, one for the electric coolant fans (if you have them).

[diggerrigger]

thanks for the reply. I'm going to check out my repair manual's wiring diagram and try to count them. I'll look for them after I know how many I'm looking for.