Check engine light.

The guy at Autozone ran a test said it cold be three things a bad battery connection (the battery did have some corrosion). Or, transmission temp sensor. There was another code but it didn't have a probable cause. We cleaned the battery and the light went off. Two days later it comes back on. I want to know what the other code means. And even though I bought it used off the owner does it still hold it's warranty.