Q: 02 sensors and catalytic converters on 2001 Toyota Tundra

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would a cracked 02 sensor give off false readings on an emissions test? My 02 senor is cracked and I asked to have it replace for I thought this might be the case of a failed emissions test. When I brought it to the dealer to be replace they said it was a possibility but refused to replace the 02 sensor. The dealer said he could not unscrew the bolts to get it off. The dealer reset my computer and said if the engine light came on again I would need the catalytic converta. Within the hour of driving around the engine light came back on. Can a cracked 02 sensor set off the engine light and give a false reading or would the computer know the difference and go off due to a bad catalytic converta ?
(2) Answers
The logical thing to do is to replace the cracked sensor it will command the check engine light to come on, the O2 sensor will let you know if you need a CAT once you replace it.
I have my light on too for both sensors. and they went bad because of the exhaust manifolds have a defect in the welds, if the warranty is still good they might replace because it is an emissions problem.