Echo OverDrive Issue

[arthursleep]

Gday

We have a 2003 Echo that has an issue with overdrive.

Basically it won't shift into overdrive. On occasion I can get it to shift into overdrive if I can get it to a decent speed 70+ seconds before the blue tempature light turns out.
This has to be timed right. Once the light is out there is no shifting into overdrive regardless of speed. When it does go into overdrive it's just for that one time, once it drops back into 3rd that's the end of it.

I originally though this might be a temperature issue and thought once the thermostat was opening the engine was running too cool, but the thermo fan still cuts in and out as if it was getting to temperature.

It's been to several mechanics and apparently it's throwing no codes so no issue can be found.

Can anyone help me out?

Cheers
Arthur