1997 Chevrolet 1500 4.3l Error Code P0420

[NathanY]

I have searched through the forums before posting this, because I didnt want to post something that has been answered. I have found posts that were close, but not same engine or vehicle, etc.

 

I have a 1997 Chevrolet 1500 with a vortec 4.3. I am getting an error code P0420, catalyst efficiency low-bank 1. I have checked for any vacuum leaks, there are none. The truck runs good. It doesnt leak or burn any oil and gets good fuel mileage.

 

Do I need to replace the catalytic converter? Is there a common problem that it might be? I dont want to just start replacing parts that are not needed.

[tbhuge]

O2 sensors. How many miles on the truck?

[NathanY]

It has 189,000. Just came on in January. Never had any problems before.

[tbhuge]

A couple things can cause this code. If the O2 sensor in front and behind are getting the same reading, that could mean the converter is not working right. Or there is an exhaust leak somewhere between the block and the last O2 sensor. Malfunctioning O2 sensor. Retarded Spark timing. Leaded fuel was used accidently.

 

I would first start and see if you have any exhaust leaks between the block and the last sensor which will be immediately after the converter.

 

If you have never replaced the O2 sensors, I would replace them next. I had a 97 s10 with the same motor and had to replace the O2 sensors a couple times while I owned it.

 

As far as the catalytic converter, they can eventually malfunction and need replaced.

[NathanY]

Update:

 

I got tired of messing with it and took it to a muffler shop. It turns out that the catalytic converter was plugged up. When they took it off you could see carbon or soot or whatever it is just falling out of it. The O2 sensor right in front of the cat was no good and had it replaced too. There were a few exhaust leaks on it, nothing major, but enough that you could hear it so I had the guy put in a complete new exhaust system from the end of the manifold to the back of the truck. That included two new donut gaskets, three new O2 sensors, new catalytic converter, new muffler, and all new pipe. It sounds great. Or doesnt, I dont know how you would say it because it is so quiet you cant hear it running when you're driving down the road. Best of all, the check engine light has not come back on in over a month since I had the work done. Total cost was not that bad either, I spent $300 for the whole system including the cat.