ses light came on

Last weekend my ses light came on, went to autozone and was P0430. Had them to remove the code to see if it came back, saturday it came back same code which is P0430 Catalyst System Efficiency Below Threshold (Bank 2)


Searching on here found it either a bad cat on pass side or a bad o2 sensor on the pass side behind the cats, but on the post no one ever gave an update on what it was.

I have a 99 gmc 4.8. has 123,000 miles on it, runs fine, still has same power , never had any misfire codes. could htis be just he o2 behing the cat? is there anyways to check the cat without driving to dealer?

thanks

The dealer or an exhaust shop should be able to check the flow. If you don't want to take it to a shop you could start by replacing the o2 sensor that is throwing the code, that is a heck of a lot cheaper that starting with the cat. The o2 sensors behind the cat usually don't go bad, but they can.

One way to tell if it's the o2 sensor or cat is to swap around both post cat o2 sensors.

If it throws a P0420 code for the other bank... It would be that o2 sensor.
If it still throws the same P0430 code... It's the bank 2 cat.

I added a pair of high flow cats to my 2000 sierra and it throwed the threshold codes.
I added an o2 simulator to trick the computer to turn off the dreaded SES light.

Thanks i'll swap the o2's behind the cats.

I might be misinformed but i though once you removed an o2 sensor, you couldn't reinstall it? or am i thinking of something else?

Thanks i'll swap the o2's behind the cats.

I might be misinformed but i though once you removed an o2 sensor, you couldn't reinstall it? or am i thinking of something else?

You are thinking of something else. No problem reinstalling an 02 sensor.

Use just a dab of antiseize on the threads but do not get any on the sensor when you reinstall.

//2000CAYukon