Check the coolant sensor plug to make sure the prongs inside are not corroded or pushed back in. Clearing engine codes is accomplished by removing the EFI fuse for 30 seconds.
Here is a helpful engine code link:
http://www.toyota-supra.info/forums/...c-codes-2.html
I have attached a photo of a typical coolant sensor area on the engine. Yours may be similar.
The coolant temperature sensor is the square plug on the side on the engine just to confirm.