2003 Toyota Sequoia P0420 code Which side 02 sensor to replace and fore or aft?

Question

I have a 2003 Toyota Sequoia with a P0420 code "Catalyst system efficiency below threshold Bank 1" Which side 02 sensor should I replace and is it the fore or aft of the converter?

Thanks,
Mike

Answer 1

Hi there,

Most of the time when you have this code the converter itself is to blame. However, if you want to try the O2 sensor first, replace the sensor AFTER the converter. This is the one that tells the computer if the converter is working properly or not.