Is the problem the oxygen sensors or Catalytic converter? on 2001 Infiniti I30

2001 Infinite I30. I had O2 Sensor Bank 1, Sensor 2 replaced in May of 2010 by a new mechanic. They recommended that, in these cars, all 4 sensors work together so ALL four should be replaced but I couldn't afford all, so I replace one and the "check engine" light went off. Light back on now. I took it to my old mechanic. The diag. code is coming up "middle catalytic converter". He says this should be replaced. I told my newer mechanic this. He says the failing O2 sensors are causing the CC to malfunction, hence the code and that I should replace all remaining sensors instead. Old mechanic says he detects no malfunctioning with remaining O2 sensors. Who's right? Help!

by in Richmond, VA on November 16, 2010
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1 answer 1 comment
ANSWER by , November 16, 2010
your old mechanic. you can test the o2 with a scanner and a scope for operation. you do not need to replace all when one fails, just the failed part. your shop can do a graph of the cat to see if it is bad or not. cats are common for failure from either age, 100k or more, or from misffires from a bad plug or coil over an extended period of time. Roy
COMMENT by , November 16, 2010
My old mechanic comes through once more....Thanks for your help Mastertech!