I have been getting poor fuel economy, and a couple weeks ago I cleared out my ecu, and found a stored code(0503). I know this is for the right bank o2 sensor, but my CEL never came on. The ecu was last reset before this 2 months ago when I replaced my ECTS. Should I replace the o2 sensor? I have just put a k&n air filter, new fuel filters, and ngk coppers. I used to be getting 24-25 and now I am getting ~20. Any thoughts?

 

u used to be getting 24-25 thats on the highway right?

 

No, my driving habits haven't changed, just mpg. I keep rpms under 3k(most of the time), and its a mix of city/highway driving.

 

dont assume its a false reading just because you didnt get a CEL. not everything throws a cel such as the knock sensor which is a ghost code. The ecu didnt just come up with it for no reason. I would replace the 02 sensor if I were you.

 

a bad o2 sensor will cause poor fuel economy and if you let it go to long (3-4 months) it will cause damage to your cat also . if you have a OBD2 scanner you can check the o2 sensors check for voltage switching from rich to lean witch is going to be around 100mV to 900mV (.1v to .9v on a low end scanner) . if you can't test that just change it you will pay someone more to test the o2 sensor than just changing it your self

 

The 2 posts above this one are correct. Go ahead and replace hte O2 sensor.