screw991le

Catalyst efficiency below threshold bank 1
Catalyst efficiency below threshold bank 2

Both came up would it be the CAT of the O2s?

Thanks

vettenuts

Those are the rear cats, do you have headers or other exhaust modifications?

RonSS

Generally a 420/430 means the PCM is seeing too much activity on the rear O2s. If the cats are warmed up and working properly the rear O2s should be “flat lined” at a very low voltage. Like .1 to .3 with very little up and down movement. So…. If the cats are being properly feed the right amount of CO and O2 (no other codes) …….It’s the cats! Several ways to deal with this.

1. Install cats the PCM is happy with.
2. Make the PCM happy with the cats you have.
3. Tell the PCM to forget we have cats and rear O2 sensors.

Of course what you do will depend on your ability to tune/edit the PCM and weather you have to worry about a smog test. And as always this is JMHO.

vettenuts

If it is the cats, one thing to note, a lot of guys are more than willing to unload their stock H pipe for very cheap or sometimes free. I would imagine they are expensive from GM. Mine is hanging on my ceiling in the basement

screw991le

Thanks, I might go with O2 sims

vettenuts

Why not just have Slowhawk edit them out, he is in SE Mass