Check engine light codes

[lmacmil]

Several months ago the CEL went on in my 1996 V6. Autozone pulled the codes which were P0133 (O2 sensor) and P0420 (catalytic converter efficiency low). The light went out by itself after 2-3 weeks. Two weeks ago it came back on. This time the only code was P0420. Should I infer from this that the converter is going and that somehow caused the O2 sensor code previously? Or could a failing O2 sensor cause the P0420 code? I certainly don't want to replace the converter if it ain't broke.

Are emission components covered by a longer warranty? I've read something about 8/80,000 miles on emission systems.

 

[Robert]

Yes, the catalytic converter is covered for 8 years, 80K miles under warranty (at least in 1997). The possible causes for a P0420 code are:

"Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.

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/tailpipe assembly.
-- Damaged catalytic converter.