I have 94 ES and the check engine light went on and off after the dealer replaced the O2 sensor, then it came back after 2 weeks, I brought it back and they said it the CAT. Converter, I replaced it, didn't help, didn't pass smog check, I brought it back and complaint, they replaced the second O2 sensor, and that fixed it. The best part was since they misdiagnosed the first time. They replaced it for free.