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I have a Pontiac G6, 2.4l-4cyl.The original catalytic converter was replaced for about 3 yrs. ago. This catalytic converter only worked for about 2 yrs. I drove with the check engine light on ( Po420) until inspection required something to be done. I bought a new aftermarket converter from amazon for about $190, and replaced it myself. The check engine light would still not clear/came back if reset. I measured the temperatur in the front and rear of the converter. The temperatur is supposed to be 100-150 dgr. farenheit higher at the rear when when converter is working. I had a little lower temp at the rear than at the front. That means: converter is not working.
Does anyone have any experience with this? I am wondering if there can be something else that case the converter not to work? I have read that a leak in the intake manifold can make the converter to not work.
Does anyone else have any experience with this?
 

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I had this issue as well on our '07. If you search you might find the post (https://www.g6ownersclub.com/forum/12-problems-solutions/45922-p0420-code-year-after-year.html). Short story in 250K miles I replaced the cat 5 times. Original went 100k. They were expensive at that time so I bought a tubular style. It cracked so I bought a Dorman. First one was bad out of the box so I replaced it under warranty 2 weeks later. It lasted a while and I replaced it. Then a year ago it wouldn't pass emissions again and so I replaced it again. A week after it passed the light was back on. P0420. Both O2 sensor voltages look good. They were replaced at one point as maintenance. I put injectors in it 9 months ago. Replaced the valve cover gasket a year ago. New plugs. Tried a fouler cup on the downstream O2 early on. At one time the state mechanic looked at it and found nothing wrong so we got passed for 1 year that way. So a month ago we sold it. This was really the only problem we had with it other than both front bearings died a week apart(and the steering that wasn't recalled for '07 but finally was). Never had a starter, alternator, a/c anything, etc. Brakes went 60k or more with GM pads. Really was a nice car other than the check engine light. I have heard that GM has a less aggressive flash for these but never found any concrete info. I considered having this code turned off using HP Tuners, but the last few years the standard changed and now all readiness monitors but 1 have to set with no active codes instead of earlier it was no active codes and had to be 1 week from a code clear. In the early days we could usually drive a week without idling at all and the light would stay off. We could pass emissions and a day or so later the light was back on when we went back to normal driving. P0420 was the only code it ever set. If it had an intake leak I could never find it. I used either GM or FelPro gaskets each cat replacement. So I feel for you. Been there, done that.
 

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Discussion Starter #3
HI,
and thank you so much for answering.
This is the 3rd. catalytic converter on this car. When the po420 code came back on, I was thinking that I would do it right and ordered a after market converter.
The light didn't clear at all with this converter, so I had to trick the sensor by installing a fowler. The light is out and I passed inspection. I know that the converter isn't operating like it should because the temperature at the end is lower that at the front. I saw on you tube that it there are a leak on the intake manifold it could cause the catalytic convert not to work. Intake manifolds are very often made of a syntetic/plastic material and can easily crack according to this posting on you tube. Well at this point I am not sure what is causing the converter not to operate like is should, and I am forced to use the fowler to keep the engine light off.
 
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