Contour Enthusiasts Group Archives Forums General Troubleshooting which o2 exactly is 420?

i recently had a code 131 and changed the top right side o2 sensor . this lasted about 2 hours (the no cel) that was just long enough to pass my emissions test ....thank god! anyhow, now i get a 420 code, is that the same side lower down? or am i way off? and why did it go out so quickly after the other one was replaced?

From the Ford TSP:

P0420=Catalyst system efficiency below threshold (Bank #1)

Possible causes:
-- Use of leaded fuel.
-- Oil contamination.
-- Cylinder misfiring.
-- Damaged HO2S.
-- Damaged ECT sensor.
-- Downstream HO2S wires improperly connected.
-- Fuel pressure too high.
-- Damaged exhaust system pipe.
-- Damaged exhaust manifold.
-- Damaged muffler/tail-pipe assembly.
-- Damaged catalytic converter.

thanks, that narrows it down, oh well, i geuss i'll start w/ the o2's and work from there...

Damn codes. Codes don't tell you what part is wrong, they tell you what part is sending an error code. There is a go/no go diagnostic tree that goes along with each code. You can get an O2 code because of a vacuum leak(leans out the mixture, O2 sensor tries to compensate...can't anymore, so it sets a code). Anyway, you can waste your money replacing parts, or you can get ahold of the diagnostic tree, a good, high-tech mechanic should be able to help you out here.