Chevy Blazer Service Engine Light

Yesterday the Service Engine Soon light came on in my 2004 Chevy Blazer. I took it to Goodyear this morning for a diagnostic test and asked them also to change the oil since it has been a long time (since Sept. 09) since I did that. (I know my bad). The tech changed the oil, etc. and told me that the temp sensor was causing the error and I needed a new coolant temp sensor, thermostat & gasket, radiator hoses all replaced, coolant flush, radiator cap and decarb for almost $500. I had to be to work so I made an appointment for tomorrow morning. But as I drove away the light went out. Could it be all I needed was an oil change?  Help please!