Yep. Quite familiar with it and have been living with it for more than a few years. In fact I have "corrected" my code 26 with strategically placed black electrician's tape over the CEL...
That having been said, it is just that - a dumb (IMO) bit of over engineering that keeps the vehicle in 2nd gear until a certain operating temp is reached. It has to do with emissions and the catalytic converter. I prefer the way mine shifts without the delay.
The fix is either simple, or difficult. There is a green vacuum tube coming from the driver's side by the firewall down to the tranny. It's small in diameter. The check is disconnect it and apply vacuum. If it holds you're lucky and the problem is the diaphram where you disconnected it. Not expensive and easy to find in parts yards. If it doesn't hold that indicates the problem is with a shift solenoid inside the transmission. To fix it requires more knowledge than the average Joe like me has, and requires taking off the transmission pan.
Like I said I live with it and have no/no problems whatsoever other than the irritating light.
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