Failed Emissions Test

[webstri]

Hi,

Ran my 1998 gmc yukon thru emissions test and failed. Two codes: P420 and P430. Catalytic converters were replaced 3 years ago.

What parts do I replace to eliminate the two codes?

[05GMCZ71]

Get it diagnosed first. Just because an o2 sensor code is set does not mean that the O2 sensor is bad, in many cases, it's something upstream that is causing the readings to go bad once the exhaust hits the sensor. Throwing parts at something hoping it fixes it wastes more money. Take her into a good reputable shop and have it diagnosed.