i have a code that says the catalyst system efficiency below threshold. does that mean i have a bad converter? can i just gut it? or will that throw off the O2 sensor. 98 accord. thanks

 

More than likely the oxygen sensor has failed. That would be why it is sensing a "bad" catalytic converter when it is perfectly fine.

 

You should test the oxygen sensor with a voltmeter to confirm it has failed, however bench testing O2 sensors doesnt work because they need to reach operating temp (around 600 degrees to function)
Pull the pigtails with the engine warm and using a multimeter test the voltage readings to the manufactures guidelines.
And don't gut your cat, your check engine light will be on forever!!

 

The secondary oxygen sensor sends a voltage signal to the ECM giving feedback of the operation of the catalytic converter. The primary and secondary oxygen sensors are essentially the same. The primary oxygen sensor should have a varying return signal. From .1 to .8 ( or so ) volts. As the catalytic converter modifys the gases from the exhaust the signal of the secondary oxygen sensor should reflect this in a more or less steady voltage reading.

If the ECM sees too many occilations in the secondary signal voltage ( meaning the catalyst is not modifying the gases ) the ECM determines the catalyst is no longer working and the DTC is set. For a sensor to fail and cause a false cat DTC the sensor signal voltage would have to fluctuate according to the enable criteria of that DTC. This is unlikely. My guess is that the catalyst is no longer functioning properly.

 

If you gut the cat, A) your check engine light will never turn off, B) your car will not run properly (due to no 2nd O2 sensor to check the A/F ratio, C) Here in South Carolina, no cat is a fine no less than $10,000.

 

well thanks guys for all the input. I will try and test the 02 sensor first but i guess im gonna go for it and buy the converter. car has 226k on it so im sure its time for a new one.

 

Don't buy a used one off eBay or some cheap POS aftermarket pretent calalytic converter. Cheap is expensive...