I have a 03 Subaru WRX 2.0 ltr, last Wednesday 12.21.11 I replaced the upstream O2 sensor because my check engine light was on. Bank 1 Sensor 1 O2 sensor was not working.
I took the car into the subaru dealership today and there are no codes being thrown from any sensors. However, when I took the car to get smogged the diagnosis machine said the Cat, O2 sensor were not "Ready". The mechanic said to drive the car more.