code 1 issues

ok my check engine light came on while i was driving, got home and checked it, it was throwing a code 1 for oxygen sensor. well i checked the oxygen sensor and it was fine .4 volts, so i reset the ecu but havent driven it yet, anyone know what could cause this?

ok my check engine light came on while i was driving, got home and checked it, it was throwing a code 1 for oxygen sensor. well i checked the oxygen sensor and it was fine .4 volts, so i reset the ecu but havent driven it yet, anyone know what could cause this?

replace the o2. The're like <$20 from autoblown.