P0420 Code On 2006 Chevrolet Malibu

malibutroublemalibutrouble Member Posts: 19
edited March 2016 in Chevrolet
Within the past year, I purchased a 2006 Malibu off of a small town used car dealer. I had taken it for a test run and inspected it myself. I'm not an expert mechanic, the only time I can fix a car is if there is a how-to video on the problem and after I fix it once, Ill be able to do it for the rest of my life. Learning little by little I guess. The car was in good shape with a few small easy tweaks. It ran perfect with no problems at all for the first 3-7 days and then I noticed the check engine light was on. I had it taken to a certified mechanic who inspected it and said the check engine light was on because the crankshaft oil seal, and oil sending unit were busted up on it, as well as a crack in the muffler, but said that there was no need to rush to fix it as it wasn't hurting the car as long as I kept oil in it. They also noticed that the P0420 code was being thrown off and told me the catalytic converter needed a more in depth inspection to find out if it needed to be replaced. But, again, as long as the car wasn't giving me any problems, there was no need to hurry into fixing anything. Later on, I had saved up some money to get the oil leaks fixed and took it back to the same mechanic who fixed the oil sending unit and noticed that the timing cover was also busted on it. I had both the oil sending unit and timing cover fixed that day. I brought it home and it ran like a dream but, the check engine light was still on. The car had ran for months with the check engine light glowing as I was saving to have the catalytic converter checked on. On my way to work one night, I noticed the car would try to stall out on me while I was slowing down or coming to a stop until I hit the accelerator. It would run just fine as long as my foot was on the gas or the car was rolling. That went on for about a week or two and the the car just wouldn't run anymore. I could start it up but, it would not make it to the end of my driveway before it gave out. I let it sit until I could get it back to the mechanic who has been working on it. I hooked a small diagnostics reader to it and it threw off the P0420 code again. I finally got it back to the mechanic, explained what was going on with it, and they called me to inform me that most of the sensors, the throttle body, intake, and exhaust manifold was covered in oil blow by as well as very little to no oil in the car, and the right front wheel bearing had some wear in it. I had it all fixed. When I went to get the car, I asked them if the P0420 code was gone, they told me all codes were gone but that they reset the throttle body and that it was not uncommon for the codes to come back when the car's systems cycled back through. Not really knowing what blow by then was, I had asked them if that problem was fixed and what the chances were that it could happen again and what I could do to prevent it for reoccurring, they assured me that that problem was fixed as well. They had the car for almost an entire day. I've been driving the car for a little over a week now since its come out of the shop, making sure to check the oil levels in it before and after I drive it everytime. As well as keeping an eye on the check engine light. This morning, I had noticed the car was a little low on oil, a quart low. I put about a quarter of a quart in it, give or take, just to get it to a comfortable level to get it home as I was out of town. I drove it home, no problems. Later, on my way home from the store, I looked down and seen the check engine light was on again. I got it home, hooked the diagnostics handheld to it and it read out P0420. Currently, the oil level is fine. Under the car, near the exhaust manifold, I noticed a rattle...Almost like a bumblebee. Exact sound. I look under it and notice that the front of the catalytic converter, nearest to the engine is putting off a good bit of heat. Like looking at the road on a hot summers day, mirage-ish but, it isn't like that on the back of the converter, nearest to the muffler.

My biggest fear is that the catalytic converter is bad on it. With a little over $1100 already in the car on maintenance and repair and having no money at all, my question is, is there a way to tell if the catalytic converter is for sure the problem without having it taken off? The mechanic told me that if the code came back to have it brought back in and they will diagnose it again to find the problem but, they are closed today and open again in the morning. It'll be a tight squeeze or no chance of seeing the car at all due to it being early in the week. Ill need the car for the remainder of the week but, I'm afraid it might shut down completely on me again. I'm doing the best I can to not drive the car until I can get it looked at. When they told me the catalytic converter needed further inspection they told me that it could possibly be replaced with a straight pipe or flex pipe which would be the cheapest option because putting a whole new exhaust manifold and catalytic converter on it would run close to $1000.

Is there a way I can test the catalytic converter without taking it off? Could it be something else? Is it true that a flex pipe or straight pipe is equivalent to a catalytic converter? How does that work? Is it better to replace it entirely or have a pipe put on it? Any videos or sites to educate me on diagnosing this problem myself?

Any and all help is very appreciated!

Best Answers


  • malibutroublemalibutrouble Member Posts: 19
    Is there a way to test anything myself?
  • malibutroublemalibutrouble Member Posts: 19
    I see it. I appreciate it very much and Im gonna get on that in the morning. I just figured Id see if I could find someone to see if they could help before I threw more money into the car. If nothing else, Id hope that breaking down and putting the vehice in the shop doesnt break my wallet!
  • malibutroublemalibutrouble Member Posts: 19
    I took the car into the shop today and they offered to do the diagnostics on it for free. He said that it was throwing off the P0420 code and went into explaining that a lot of the time, its not the catalytic converter but other problems that interfere with the sensors readings. He tested both 02 sensors and said that they were working the way they should. On the spot, he ruled out any problem with the catalytic converter but, like you, thinks its an exhaust leak causing the computer to misinterpret readings. They scheduled me in for Wednesday to have the problem inspected fully. If the 02 sensors are working on it, would there even be a slight chance the converter is bad? He said he doesn't see it hurting the car to drive it, at least until we get the problem pinpointed.
  • Mr_ShiftrightMr_Shiftright Member Posts: 64,481
    As long as you don't have a BLINKING check engine light, then there's no harm done to the catalytic. whenever the check engine light blinks, you should shut the car off.

    He should also check for a misfire, exhaust leak and vacuum leak. Good luck with it!
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