i got a 2002 accord 2.3 ltr 4 banger and i cant seem to get it to pass the smog test here in nevada. i just replaced the cat and the lower sensor on the car. and it is still throwing a code for the cat being bad. my question is do i need to replace the upper sensor as well?

 

what brand did you replace the cat with? and the cat oxygen sensor?

you can use an infrared thermometer to check the cat's efficiency. It should be very hot, 400 to 600 degrees F

 

What part of the test are you failing? CO, NOX,...?