i just got a p0136 code this morning and cleared it. it hasn't returned yet but i' also have my crappy aftermarket cat falling apart inside. think this would cause the sensor to throw the code?? thanks

 

I get the P0136 code on highway trips when the Maxima has a silencer in the exhaust pipe end. If I run without the silencer, the code stays away. I thought it was a problem with the Magnaflow HFC but I've realized it is caused by the silencer exhaust obstruction.

 

so, yes?? maybe??

 

Possibly so. Maybe another member will confirm. In my case it occurs when the exhaust cannot flow freely.

Has the O2 sensor been replaced?

 

O2's don't measure flow rate, they measure oxygen levels.
Will they fail if an exhaust system part fails, probably not.
Will they throw a code due to a failed component, in some cases, yes.