Exhaust leak and P0420 code

[WobblyElvis]

4 cylinder 06 ecotec developed a small exhaust leak aft of the CAT a month ago. I didn't have time to do anything about it so I left it. Yesterday code P0420 [inefficient CAT] popped up. The leak is about 12 inches past the converter and I'll have it repaired next week. What are the odds repairing the exhaust will be all that is needed?

I'll post the results. Lucky that there are no more emissions tests here.

 

[StevieC]

P0420 doesn't necessarily mean the cat is bad. Check the sensor is operating properly first and fix the exhaust leak.

 

[xxch4osxx]

Originally Posted by WobblyElvis
4 cylinder 06 ecotec developed a small exhaust leak aft of the CAT a month ago. I didn't have time to do anything about it so I left it. Yesterday code P0420 [inefficient CAT] popped up. The leak is about 12 inches past the converter and I'll have it repaired next week. What are the odds repairing the exhaust will be all that is needed?

I'll post the results. Lucky that there are no more emissions tests here.


They are still doing emissions testing up till April of next year.

 

[Brybo86]

I'm gonna guess 95% chance the leak fix will clear the code.

I recently used "versachem" muffler weld on an exhaust leak and code hasnt come back since

 

[slacktide_bitog]

Is the leak after the downstream/post-cat oxygen sensor? The post-cat o2 sensor is what determines that the cat is no good.

If the leak is before the sensor, repairing the leak might fix the issue. If the leak is after the post-cat sensor, then you probably need a new cat.

 

[Trav]

If the leak is within a foot to about 18" of the rear of the rear o2 it can cause the rear o2 to read false. Normal engine pulsations can draw the ambient air drawn in through leak upwards and reach the rear o2.
This happened with Nissan cats that were mounted close to the head, the ceramic got drawn upwards into the cylinders, same principal.

Fix what you know is bad before chasing any other issue.

 

[wdn]

Same thing happened on my Gen 1 Tundra there was a leak at a rusted out 02 sensor bung itself and also section of pipe with pinhole leaks. 90 bucks worth of exhaust work last January and the P0420 has never recurred. Same 02 sensor was reinstalled and was fine.

 

[rubberchicken]

I had a similar problem with my 06 Saturn Ion Redline (2.0 supercharged) - I found that the ZZP stainless exhaust parts were less expensive than factory and fully EPA compliant. I also replaced the O2 sensor using a AC Delco or Bosch (cannot recall) part from Rock Auto. There is a typical problem with those exhaust systems where the accordion coupler to the manifold fails. If its JUST the coupler, ZZP has a weld-on replacement for about $25.

 

[WobblyElvis]

Success! It appears this problem has been rectified with a simple exhaust system repair. I took the vehicle to a muffler shop Tuesday and found a leak in the exhaust where the flex pipe meets the exhaust about 12 inches aft of the 2nd O2 sensor. The leak was repaired and the fault code. The P0420 code has not returned. Funny how an exhaust leak aft of the O2 sensor can set this P0420 code but it appears to be true. Some of the above posters were right on the money. Thank you.

 

[StevieC]

Glad you got it sorted. Yeah exhaust back pressure not being correct can cause codes like these, glad that is all it was.