jtlonghorn

'00 1500 w/ 105,000 miles throws the PO420 code. Freeze frame data is the following:

Fuel Sys 1 and 2 are CL
Calc load 1.96%
ECT 197 F
STFT B1 0
LTFT B1 -3.13%
STFT B2 .78%
LTFT B2 -3.13%
Map in Hg 11.22
MAF .74
TPS% 0

Thoughts on where to start? Not sure which to address first...O2 sensors or the Cat itself. Additional testing procedure recommendations would be appreciated. Thanks.

EinST

P0420 is almost always a catalytic converter problem (spoiled, burned, or fused). On the scanner the upstream O2 sensor will normally bounce back and forth between .2-.9 volts. When the catalytic converter is doing its job, the downstream O2 sensor will read steady at ~0.45 volts. P0420 says it bounced around instead. Mind, this is very unlikely to be caused by the fault in the sensor, wiring, or exhaust leak near the sensor.

MDTAHOE

99% are bad converters. If you use a cheap replacement the repair may not last long 6 months maybe a year. We always in tall dealer cats at work for the reason.

jtlonghorn

Sounds like I'll be replacing the converter...which ones should I look into buying that should last and which ones are garbage that I should stay away from?

Also, is it worth spending the money to have it hooked up to the scanner to look at the O2's?....I'm thinking not.

EinST

Like MDTAHOE stated, consider getting it from the dealership parts counter. The problem is, sometimes they come in two's in a Y-assembly and you only need one bad one cut out and replaced. I guess it all depends on how long you you intend to keep your vehicle.

Just to cover all basis it wouldn't be a bad idea to verify how the O2 sensors are reading in close loop. You may want to look into a decent scan tool among hand-held units or ones that do USB or WiFi interface to a laptop or smart phone, etc. They aren't terribly expensive nowadays. I myself have been considering the latter.