Service engine soon

[Scupper]

2000 GMC Yukon XL 5.3 4x4. 160,000 miles.

Plugged in the analyzer and there was 2 code readings.

First code was PO420 bank 1. Catalyst system below threshold.

Second code is PO430 bank 2. Catalyst system below threshold.

Upon returning analyzer and inquiring as to what the codes were I was met with less then desirable information. The people at the parts store did not know and could not look up the code for many reasons...

From the parking lot I called a different auto parts dealer and shared with that person the codes that I just read.

He told me they were for O2 sensors, front and back and which ones do I want. I told him both and he replied that there are 4 sensors and I need to be more specific.

Is there an easier way to more specific or do all 4 of these sensors need to be changed? Also, any tricks or hints if I tackle it myself?

Thanks...

[deadeye]

Well, I dont think that they are for the oxygen sensors themselves. There is a chance that the downstream (after the catalytic convertors in the exhaust) sensors (2) are bad as they are the ones directly responsible for giving you the catalyst system below threshold codes. However, before you throw some sensors at it check them to be sure thats the problem. Generally, if that code pops up the catalytic convertors are failing. Those sensors tell the computer if the cats are still doing their job and that code says that they are not. If you let the catalytic convertors go too long they could plug up and give you a whole other set of problems.

The sensors (2) upstream (just after the motor on the exhaust) are the ones that help adjust the air/fuel ratio and wont have anything to do with that code. They help the engine run smoothly and efficiently by reading how much oxygen is left in the exhaust.

I would get a shop manual and see what the tests are for checking those sensors before throwing parts at it. If I were to take a shot in the dark, I would say the cats are going bad. With that many miles its completly possible that they need replacing. But, check the sensors first since that would be the easier/cheaper fix.

[Scott K]

As deadeye said 420/430 code is for how the cats are performing. You would need a scan tool that can graph the o2's to see how the cats are performing. I would do this before parts replacement, as cats can be very expensive, and rear o2's arent cheap either. Then if the cats are bad, you will need to see if something caused the cats to go bad, or the new ones will go bad as well.

[Jeremy airjer W]

I think that has the Y pipe cat assemblies. If so it is pretty common for these to have those codes and have bad cats!

[Scupper]

Hey Fellah's...

As usual, you guys were dead on. Original equipment (160,000 miles) Cats on the Y pipe were failing. New Cats and sensors and should be good for another 50K.

Ouch!!! That was an unexpected expense.

Better then breaking down on the road and scrambling for a tow, mechanic/tech etc, etc, etc.

Thanks for sharing your expertise.

Good Luck...

[deadeye]

Im glad you got it fixed. That is a expensive one but better than waiting and having other problems.

[Jeremy airjer W]

Another satisfied customer! Should be good for another 100k!