Check engine light came on two nights ago, truck wasn't running rough, idles smooth, no backfiring, no smoke coming out the exhaust, etc. Took it to AutoZone to get it scanned because I cleared it yesterday just to make sure it wasn't a fluke. Here is what I got from AutoZone..."P0420 - Catalyst efficiency low - bank 1.....Probable cause: 1. Catalytic converter defective {failure possibly due to 2, 3, or 4) 2. Engine misfire or running condition 3. Large vacuum leak 4. Engine oil leakage into exhaust valve guide seals, pistons, rings.

I am thinking catalytic converter failure due to misfire since I had the plugs all replaced at the dealership because of a serious misfire issue a few months ago and the result of the misfire has just now manifested itself.

Second opinions?

 

Eh... have bank 1's o2 sensors tested... replace if necessary.

If you have a California emissions, there is an upstream and downstream sensor, and if you just have regular emissions, theres only a downstream sensor.

 

Thought about that before I went to bed. I'll probably take it to an exhaust shop nearby and hopefully they are still open after I get home from work.

 

It's at the dealearship right now, didn't like the guy at the muffler shop telling me his code scanner was better than the one at AutoZone just because it cost more, a code scanner is a code scanner. That and if it is the cats they are still covered under the emmissions warranty.

 

I'm betting it's a bad passenger side cat.

A code scanner is not just a code scanner - the more expensive ones can do a lot more than just retrieve codes. For example, the Autozone scanners cannot retrieve manufacturer-specific stuff like tranny codes.

 

Ended up taking it to a different dealership, called at 1030 after I had used the after hours drop the night before and kind of got the runaround by the service guys there. Called again at 130 to see if anyone had looked at it, no "but it's getting up the line." Took it to the dealership that did the plugs, was impressed with the service I got there.

The question though is it both of them or only one and what caused the failure is my concern. Ticket from autozone said it could have been caused by a misfire which it had really bad misfire problems so I had the plugs changed at the dealership, all 8 out in one piece.

 

Yes, a misfire can be hard on cats.