P0420 code

[Mike_D47]

I have a 2002 Silverado LS extended cab, RWD, 4.8 truck with 170k miles. While driving home yesterday, the service engine soon light came on steady on the dash. I took it to Autozone to have it the OND II read. The tech at autozone said it has a P0420 code, which indicates a problem with the emissions system. 

 

Any advise before I start changing parts?  

[davester]

maybe try to figure out where the problem is before swapping parts?  That code can result from a variety of problems.

[mikedeezxxx]

Bad catalytic converters or o2 sensors. I’d start with o2 sensors.


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[tbarn]

Tech at Autozone? Lmao. On a more serious note, p0420 will be cat convertor 99% of the time.

[sefiroxx]

Try downstream o2 sensor then cat.

Use a meter to pull o2 voltages to see which is out of wack. Then inspect upstream o2 to see if it is not normal - indicating a possible problem on that side.

[swathdiver]

A loose O2 sensor can cause this code.  Very rarely it is a bad sensor.  Eliminate that by swapping sides and see if a P0430 gets thrown.  

 

It's probably a cat and if so, stay away from the Chicom ones as they will barely last a year or so.

[Wayne3593]

O2 sensors have their own code, my '01 threw a P0135 for bank 1 sensor 1 O2. Shouldn't the code reader tell you which side?