Check engine light came on and I brought it to Autozone for a free readout. They indicated it was P0421 - "Warmup Catalyst Efficiency Below Threshold(bank 1). Anyone know
what I should be looking at to fix this? I am leaning towards a new O2 sensor but there are 2 and they aren't cheap. My car has 150,000 miles on a 4 cyl.
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