I have been having a intermitant P0420 code (Catalyst System Low Efficiency) pop up on/off for the last several months. It usually goes away in several key-starts once is showns up. Never seems to affect running performance at all...

I called the dealer and they said it most likely is the cat converter, but could be a O-2 sensor also. Because the car has 55K on it he said it would only be covered by warranty if it was the converter. I looked at the system and there is no apparent damage or loose wiring, etc.

I have a feeling if I take it in it will probably be the sensor and I'll end up paying over $200 in diagnostic fees etc... Before I make a decision on taking it in, I at least thought I'd ask if anyone else had trouble with their cat in the SS model? Any other experiences with this code?

 

Huh? The O2 sensor is as much a part of the emissions system as the cat, should be covered.

 

The GM catalyst monitor is very "robust", if a P0420 set and there are no exhaust leaks or modifications, it needs a catalytic converter. The question would be "why did it fail?". Converters do not fail at that mileage without a reason.

 

Generally speaking that's true. However, it's worth noting that the LNF vehicles use a wideband O2 sensor in the front, and they are not known for their long life compared to narrowband sensors. Also, the cat life algorithms were developed by Bosch and their subcontractors, not GM or Delphi. Even still, my money's on a bad cat. I'm scratching my head as to why the dealer would say that O2 sensors are excluded from the emission warranty.

 

Okaaay. Have you any documented cases where a defective WRAF caused a P0420? Are you aware of what it takes to set a P0420?

It's not covered. Refer to SI docid: 1873249 for 2008 HHR

 

I agree that it seems like the sensor system should be covered by the emissions warranty also. That is an intregal part of the whole system and it needs top be functioning properly to do its job.

You know, I have a hard time believing the cat would be bad also. It seems to be running fine and it sure isn't that many miles... The one thing I wondered about though is with all that black soot that cruds up the exhaust tip, is that potentially plugging up the cat as well?

 

there is an eazy way to check the converter with a non-contact thermometer also known as a tempature gun. if you can get your hands on one check the temp, before, after and at the converter its self. if they are all about the same temp then the cat is not working. at normal engine temp a good working cat, will be several hunded degrees hotter than the pipes.

 

there will be no driveability issues with that code. it simply means the cat. isn't " cleaning" the exhaust as it should. the cat. needs to be replaced, & is always suggested to replace the rear o2 sensor as well in order to eliminate the possibility of a comeback.

 

The oxygen sensor is considered a wear part. I assume the computer compares the values of the oxygen sensor ahead of the converter with the one behind it. If they are going to replace it anyway, you might as well do it yourself first to see if it solves the problem.