P0420

[Reineke]

Hello, The gf's 00 Silverado with the 5.3L has thrown a code P0420 and searching on here the possible solutions to the code show that the cat may be bad and to change it out. Well, I have a new cat on the truck now and still have the code. I believe that if the o2 sensor(s) were bad that they would trip a code of their own. I am only getting one code. I have allowed the 3 cycled to occur on the cat and same issue. The guy at the muffler shop looked into the cat and didn't see anything wrong with it, not a scientific approach, but I would think that he would have seen a bad cat or 2... Does anyone know where I can go from here?

[Norseman]

This might be a dumb question but did you clear the codes after the new part was put on?

[1999 Tahoe 4x4]

This might be a dumb question but did you clear the codes after the new part was put on?

 

<{POST_SNAPBACK}>

 

 

Your question is valid, but I have just checked the book.

 

It say's that: The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. So I guess it should have gone off already if the problem got fixed.

 

Accoding to the book the code is called: DTC P0420 Catalyst System Low Efficiency Bank 1.

 

Reading the trouble shooting the book basically 1st suggests to check for if it is the right cat, check for leaks, mechanical damage etc. I understand it is an aftermarket cat? Maybe the wrong type or size?

[Reineke]

Thanks for the input. The aftermarket cat that was used was the same type of cat from the same muffler shop that cleared a p0430 on a 00 GMC Yukon 4.8L, so I would assume that it is an ok replacement. I think I would also hear an exhaust manifold leak. There has been no damage to the system. Just a little 2wd highway cruiser that goes to town and back with the occasional 50lb dog food bag thrown in the back. Exhaust leaks around the cat were checked after the new one was in place. Any chance that the downstream o2 sensor for bank 1 could be reading incorrectly without causing its own code?

[95Sierra2500]

It's possible for the sensor to be bad, but I'd recommend going to autozone or another parts store and having the code cleared and see if it returns.

[1999 Tahoe 4x4]

It might be an idea to inderchange the sensors with eachother to see if the problem changes.

[Reineke]

Alright, will give the free fixes a chance before spending $90 on a sensor. Will keep you posted.

[Reineke]

Well, I got an OBD2 all in one last night in the mail and hooked it up to the 4.8L Yukonto geta base line reading for the o2 sensors. The cleared the code on the 5.3L and monitored the o2 sensors and they look to be reading the same as the 4.8L. Also compared bank 1 with bank 2 for readings and they looked the same. So hopefully just clearing the codes is all it needed after a cat change. Will post if the problem returns. Thanks for the helps!

[mshell56118]

Well, I got an OBD2 all in one last night in the mail and hooked it up to the 4.8L Yukonto geta base line reading for the o2 sensors. The cleared the code on the 5.3L and monitored the o2 sensors and they look to be reading the same as the 4.8L. Also compared bank 1 with bank 2 for readings and they looked the same. So hopefully just clearing the codes is all it needed after a cat change. Will post if the problem returns. Thanks for the helps!

 

I was told by a guy that used to work for a dealer that an emissions code will not clear itself. They have top be actually cleared with a scan tool. Hopefully your code does not come back since it has been cleared