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1998 Chevy Cheyenne C1500 codes: P0420 catalytic converter P0131 oxygen sensor

1998 Chevy C1500 4.3L V6 170,000 miles

My truck is stumbling and losing engine power sporadically. When this is happening I can usually drive it if I am real easy on the gas and slowly build up speed but if I mash it the engine will eventually just die completely. It has had this problem off and on for several years and now it’s back with a vengeance. It always seemed to happen after a heavy rain but now I’m not sure.

Last week I had a mechanic look at the codes and he cleared them saying that once it happened again the code(s) that showed up would be a good indicator of the actual problem. The codes that were there were for a couple O2 sensors, catalytic converter and loss of vacuum I think. It happened again and his shop was closed so I got it read and cleared somewhere else and it was P0131 bank 1 sensor 1 and since I knew that one had come up before I went ahead and replaced it myself.

The next day the CEL came back on without any noticeable engine trouble. That was yesterday, this morning it rained and the problem is back and I went to get the code read and it was the P0420. There was also C0281 stop lamp circuit somethin or other that was new.

My gas mileage has stayed pretty good this whole time, always 15+mpg. Just wondering if my catalytic converter probably needs replaced, if I should replace other O2 sensors, or if this all might indicate something else in the engine.

Before you replace that cat, you might want to pay a few bucks to get a proper diagnosis, just to be sure

And if the cat needs to be replaced, does any of this ring a bell?

Blown head gasket
leaking intake gaskets . . . extremely common on this engine
Excessive oil consumption
Leaking injectors
Ignition misfires

If you’ve got any of that going on, the new cat may not survive long

I have had to add oil recently between changes and when I had the oil changed about a week ago they said I had a leak and sold me an additive to try and fix it. Other than that I don’t THINK I have had any of those other engine issues.

Just to add something else I really probably need to get new plugs and wires since they are all probably original.

Do the plugs and wires before you install the cat

Get AC Delco plugs and wires . . . not much more expensive

Any idea where the leak is coming from?

OK, as far as plugs I’m pretty sure OEM are iridium, should I stick with those or is platinum better?

I think he might have said rear main area for the oil leak.

Use OEM plugs, probably an upgraded part number now.

Yes the original part # is out of production but there is an equivalent.

The OEM equivalent AC Delco plugs are just a few bucks more per plug so that’s no problem but the AC Delco plug wires are $50 more than other brands. That’s kinda hard to swallow.

I think I might go ahead and replace the other O2 sensors since they are all original and another had given a code before. I know these code don’t mean to automatically replace the part though and that’s kinda why I have avoided replacing them for a long time while I tried to find out more specifically what is wrong. Any thoughts on this?

From what I can see there is one more upstream O2 sensor (bank 2) and one downstream. Anyone know if I’m missing one?

Thanks for the advice I’ve received so far.

Sensors that are switching too slowly can generate P0420 code

The lowest # codes should always be addressed first, so fix P0131 first and P0420 may go away on its own.

Yeah I replaced the corresponding O2 sensor for P0131 and it has gone away but the performance problem and P0420 still persist.