My 2004 corolla was reporting this code which I understand is EGO Sensor Circuit Slow Response (Bank 1 Sensor 1).
The light came on for a few days in very cold weather. Then went away for a couple of weeks. Came on again for a few days in very cold weather. Then went away for several weeks and is still off. Occasionally the idle is too high or a little unstable. Then ok for days.
Is it most likely a slowly failing upper o2 sensor?
What should I check next?
Steve