Toyota Repair: Check engine light, voltage waveforms, toyota avalon

Question
Good evening.  I own a used 1997 Toyota Avalon XL (AT).  When I purchased the vehicle, it had 154K miles on it.  Last year, the check engine light came on.  The code was P0150 which I believe is related to the front O2 sensor (near radiator?).  I did not replace the sensor.  Anyway, the check engine light went off after several months and stayed off for many months.  Recently, the check engine light has come back on and gone off 3 different times within the last 1-2 months.  This time the code is P0420. Is there any chance that these 2 codes (P0150 and P0420) are related to the same underlying problem?  

Thank you for your help,
Chitsky  

Answer
Yes the PO150 code indicates a malfunction with the bank 2 O2 sensor, the PO420 code indicates a malfunctioning catalityc converter, you can try replacing the O2 sensor first to see if it eliminates both codes but if the 420 comes back the cat converter needs to be replaced, the O2 sensor can affect the cat converter performance but the cat can not affect the behaviour of the #1 O2 sensor located upstream of the cat, however it can affect the sensor behind the converter, the performance of the converter can be checked with the onboard diagnostic scantool by comparing the voltage waveforms of both sensors in real time, if the waveforms of both the #1 and the #2 sensor(behind the cat) are identical then the converter has failed and is not working, any toyota dealer should be able to do this simple test.