ok started off with my check engine light coming on and saying catylist effency below threshhold (bank one) and was told and was told and kinda figured it was the O2 sensor on the manifold...well i bought a brand new one and put it on and then the day later it came back on took it to autozone to have them earase it b/c i was told even tho you disconnect the battery it sometimes doesnt earase it from the computer, so i went a few days mayB a week and a half and hasnt came on...well today it came back on and im lost as to what it could be? is there anyway it could be the O2 again or mayB something else? could it be the O2 after the cat? and just to avoid questions its a 96 civic with a D16Y7...stock header

 

get a new cat?

 

there are 2 o2 sensors. primary and secondary.

 

yes i know i replaced the primary(before cat) b/c thats what the reader showed and then i just got it done again and it came up the same thing im going to try and replace the O2 again since it have a three month warranty...but any other ideas just in case...and the cat couldnt be it since its the one before the cat...

 

what all is the scanner showing???

 

edit: you may just have some loose wires somewhere....

 

Basically this means that the oxygen sensor downstream of the catalytic converter on bank 2 (passenger side) is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
There is an exhaust leak
Next step is to measure the voltage at the oxygen sensor on Bank 2 (the passenger side rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

 

For bank 1 it's either

Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing

then test the voltage like stated above^^

 

dont rememeber the number but it said exactly catylist effiency below threshhold (bank 1) thats it...so if its the second one it could be showing the first one being wrong?

 

check em both.