im thinking the cat on the prelude (h22a4) is bad. the car is throwing a code at me (PO420 - catalyst efficiency below threshhold) now heres the twist.

i've been running the car while my laptop is hooked up to it....watching the hydrocarbons...out of nowhere at no specific point the o2 sensors read taht the hydrocarbons zero out. and then the o2 sensors shut down. triggering the CEL.... should i try replacing the catalytic converter or should i take the dealership up on its offer to buy back the car?

 

You're contemplating selling your car because one of two $55 parts is bad? Yeah, go ahead and sell it and buy another Probe.

 

The hydrocarbons zero out? Are you running a gas analyzer on your laptop? Or is the sensor voltage is going to zero? Are you reading both O2 sensors? What is the LT fuel trim? When the PCM is running the cat moniter and notices a problem, It will ground the signal voltage and run on a predetermined program. This might be what you are seeing. Need to know what happens with both O2 sensors BEFORE you notice the zero out condition. You very well might need a cat. Cheaper than a Ford Probe

 

yeah im running the gas analyzer on the laptop....

yes i am reading both O2 sensors.

im not sure of the fuel trim... all i know is that the o2 sensors zero out and then shut down entirely.

 

What scale are you reading the 02 sensors on?? and what is the reading of the post-cat 02??