ETS/CE light

Got another one that is oh so enjoyable!! Check engine light @ ETS light comes on and goes off every so often simultaneously. It'll be on for a day, off for a day....any ideas on the cause of this, bad sensor maybe??
Thanks....

I have the same problem with my 96 Chevy Cavalier, the light (ETS & CE) come on for about a day or so then go out, it happens every 3-4 weeks, it doesnt seem to be anything serious, transmission seems fine, i just got the head gasket sealed and water pump replaced, along with radiator hose (replaced today) i have no idea what its about, possible emissions?

anyone?