so like a month and a half ago i got an 04 09 code from my ecu. i looked on the FSM and found out that that code was the code for my 02 sensor closest to the rear of the car. so i bought a new bosch 02 sensor and replaced it a few days ago.
now, this morning, my CEL came on again with a 04 09 code. WTF??!?!?
did i need to reset the ECU after replacing the 02 sensor or somethin? whats goin on, my car is running perfect, and getting good gas mileage and stuff so whats up?

 

yea you gotta reset the ecu after u install it, reset the ecu and the code should go away.