198k replaced the upper sensor still codeing what next

 

catalytic converter.

 

Man I just sold a converter for that car.

 

How do you know it actually needs a cat?

Use a scan tool and log secondary O2 voltage first, then show us your results.

 

ok i will do that and get back. thanks

 

what should the voltage be for the secondary o2? i get that code once in a great while but i just erase it

 

Its not the voltage per se, if the computer sees that the secondary sensor is copying or nearly following the primary sensor then it appears that the cat is not doing its job. But it may not be able to do its job if the engine is not burning properly.

If the rest of the fuel control system is out of whack and the engine is too lean or too rich then there is not enough free oxygen and extra HC in the cat to allow what we will call a controlled fire in the cat to keep it hot so it can clean up slightly out of range emissions. So lets say that the cat gets too lean or too rich to operate properly.

In the end, a Cat Efficiency code may have nothing to do with a bad cat, more diagnostics is needed and it can get deeply involved without the proper test equipment such as a 5 gas analyser.

To answer you question directly, the voltage should be in the same range as the front sensor, approx .1VDC to .9VDC but it should not have too many crosscounts (crossing .45VDC too often).

 

well he didn't provide information as to whether he changed the Catalytic converter or not, so i gave him a simple answer based on my assumptions. To make it simple without confusing him, it's most likely his catalytic converter. accords tend to have the p0420 code a lot. I've had that code when i used to own my accord also.

 

if the secondary o2, the one on the cat .. if it was to foul out and go bad would it give a different code or the same code for the cat?

 

You cant have a code P0420 without a secondary O2 sensor or downstream sensor or sensor 2, its job is to report cat efficiency to the ECU.

 

oh ok ... i use to get the same code ... i change the primary o2 ... i swapped out the cat from my '99 accord ... and the code kept coming back ... i just said fudge it and left it and just erased it whenever it would come on ... eventually it just went away ... once in a long while it comes on but i learned to live with it

 

Its not most likely the cat, as Duane stated more diag work needs to be conducted. The downstream O2 sensor should hover around 450mv. Any deviation from this will cause the code to set but the cat it self may not be at fault, it may have more emissions then its able to handle because of some other issues with the engine...