p0420 help

[Steve A]

How so Steve?

O2 sensors are installed pre and post catalytic converters, The 0420 code I believe is reduced efficiency of the affected cat, which is nothing more than a comparison of the pre and post cat O2 sensors for that bank. The post cat sensor maybe within acceptable range but the comparison may indicate a reduced efficiency cat when there is nothing wrong with the cat itself because of a "lazy" O2 sensor.

 

[swathdiver]

A crawled under my truck to swap downstream sensors from side to side as I'd been getting a P0430 daily. Noticed that right side cat was not original and that it was discolored and the sensors wouldn't budge with just a wrench on them. I concluded from those observations that the cat was really at fault. Lord willing, by the end of the week I'll have two new cats underneath and will see how she drives before dropping $200 on 4 new GM O2 sensors.

I do remember now having a constant supply of new O2 sensors for the Grand Nationals, the additives and race fuel quickly degraded those old 1 wire sensors and the cars would slow down until we put a fresh one in. The GNXs had a differently calibrated O2 sensor and we used those.

 

[FinalBreath05]

Can anyone tell me what I'm looking for while I look at the data for my Yukon? What should my fuel trims be? 02 voltages. What should the wavelength look like for the 02? Bank one sensor 1+2 both have the same wave. Bank 2 1+2 have different waves.

 

[Scottydoggs]

long term trims in mine stock were +4 to +8 went leaner wot.

in a perfect world you need a tuner to bring them values closer to zero. ive been tuning on mine goet em to + 2's all over the place and the wide band is in a happy range, so im good with em there.

o2 voltage is supposed to move up and down pretty fast if one is slow its getting lazy on ya. aka wearing out.

 

[swathdiver]

Ideally the trims should be 0% but a few percent either way is normal. Both banks should look nearly the same. If not, you should look at other things like injector pulses, misfires, etc.

 

[FinalBreath05]

I can view basically anything with my scanner, the problem is I don't really know what I'm looking for.

 

[Scottydoggs]

I can view basically anything with my scanner, the problem is I don't really know what I'm looking for.

long term fuel trims, short term fuel trims, o2's, bank 1 sensor one and two. bank 2 sensor one and two.

o2 voltage. and theres another o2 pid to scan that shows its range its working in. like wot should be in the 930 range iirc. if its not holding steady wot that o2 is bad for sure.

 

[FinalBreath05]

long term fuel trims, short term fuel trims, o2's, bank 1 sensor one and two. bank 2 sensor one and two.

o2 voltage. and theres another o2 pid to scan that shows its range its working in. like wot should be in the 930 range iirc. if its not holding steady wot that o2 is bad for sure.

I know what to look for, but IDK what good and bad numbers are.

 

[FinalBreath05]

Can I use an O2 simulator as a temporary fix?

 

[Teeroy78]

Can anyone tell me what I'm looking for while I look at the data for my Yukon? What should my fuel trims be? 02 voltages. What should the wavelength look like for the 02? Bank one sensor 1+2 both have the same wave. Bank 2 1+2 have different waves.

Hey Matthew,

From the service manual, short and long term fuel trims should be "Near 0%".
The HO2S sensors for both banks, sensors 1 and 2, just state they should be "10 - 1000mV and varying". In my truck, both "sensor 1"s pulse pretty regularly from about 65mV to under 900mV. Sometimes they are in phase, sometimes they aren't, sometimes they are the same width, sometimes they aren't. My "sensor 2"s don't fluctuate that much (at least at idle) and tend to be in the 600-700mV range. Don't take my sensor 2 values as what they *should* be, though, as my LTFT at idle aren't zero, they are between -10 and -14% currently.