2007 Lucerne 3.8 - Catalytic converter failure at 27000 miles ????

century61

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So, My mother (84yrs old) decided she wanted a new car. She offered me her old one. This thing is like mint condition. However, There are some paint scrapes where she was not able to negotiate the garage. I'll have to buff them out. The interior is absolute like new. Its got all the bells and whistles for that year. Runs nice. However.... The other day my GF was driving it and it came up with the dreaded P0420 error.

I got my scanner on it and it shows catalytic converter efficiency low - Bank 1 Sensor 2 - Which is of course the downstream OS2 sensor. The wave form on S2 matches pretty much that of S1. So, I am facing a possible cat replacement.

My question is - How can this go bad so quick???

There are no other error codes. I checked the STFT and LTFT and they are looking good. LTFT is about 0 and STFT is about 3. Man, Thats great. I dont have a problem buying a new cat its just I didnt expect this thing to puke with such low miles. I have not had a chance to get under the car yet and look at the exhaust. Probably do that today. There is no smoke out the tail pipe like an intake leak or anything like that. Oil is nice and clean. Coolant is fine.

Weird.
 

okcrum

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2008 Lucerne CXL
Does the P0420 reappear right away, after being cleared? You could try cleaning or replacing the back O₂ sensor. It's pretty much there to check the cat, so it shouldn't affect the fuel trims. At 27k miles I'd suspect the sensor or its circuit before the cat.
 

2007LucerneCXL

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Checking the O2 sensors wiring and connection may be the first thing. Not sure if the vehicle is exposed to animals or environment, has had a recent undercarriage wash, any repairs that would be near a sensor or just hasn't been driven. A spirited drive on the highway to get the system blown out and up to operating temperature may be in order, toss in a bottle of Cataclean as a additional option.

While anything is possible a failure of the convertor on this low mileage vehicle is somewhat unlikely.
 

century61

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Thank you for the replies. The weather here is suppose to be pretty nice in the 50s so I will be under the car today to check the O2 sensor. I was hoping that would be it instead of a cat. Heaven knows what my Mother has done with the car. Evidently her eye site is going because she has caught the side of the garage a few times - lol. "MOM! Be careful!".

@okcrum - I cleared the code late last night. I will take it for a test drive today and see if it comes back right away. Would an exhaust leak before the sensor cause this too?

Dang, This is such a sweet car. I will try and post some pics or a video. Its like it came right from the factory today. Amazing.
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2007LucerneCXL

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Hopefully it's a simple fix. The reason I mentioned getting it out on the road is finding the super low mileage vehicles in the 70's and the exhaust was shot because the system never got heated up enough to remove the moisture and carbon build up.
 

LARRY70GS

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98 Riviera, 70 GS455 Stg1
What usually destroys a catalytic converter is rich running, or misfires that subject the cat to un burned fuel. That overheats it and does damage. The cat could also be rotted out from the aforementioned water in the exhaust/little old lady short trip driving. If the fuel trims look good and the misfire logs show zero, chances are the cat is fine. If visual inspection shows no damage, and the engine runs good, you can either try replacing the O2 sensors, or you can add a spacer to the one in the rear.


Read the answered questions and reviews.
 

century61

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Well Folks, I gave it my best. That O2 sensor has certainly become 'one with the car'. My air hammer managed to round it off a bit and not budge it. I was going to go out and get a MAP torch and heat the life out of it but ran out of time. Therefore, I put the sheild back on decided to take it for a test drive and monitor the O2 sensors. I drove it about 25/30 miles and it did not throw a code. So, I do believe as others have said that the cat is fine. Perhaps the car just needed a good run to blow some stink out of it? I will keep monitoring it and if it throws another code I will probably have to have a shop replace it.

On jack stands I do not have enough room under the car to really work on it. I cannot get any leverage. At least its working and I have time to figure out another plan to remove it if need be.

sure is a nice car. Weather was great yesterday and I drove around with the top open :) .
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2007LucerneCXL

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I have found if these vehicles sit for extended times and/or are not driven to get up to the full operational temperature they can toss phantom CEL. Had a few over the years where I check the code, know it's not real and clear it never to be seen again.

So take it out and "drive it like it's stolen" a few more times which should hopefully clear out the entire system. As I mentioned Cataclean unfortunately it may require more driving than what the vehicle may get just something to mindful of if adding anything to fuel.
 

century61

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I have found if these vehicles sit for extended times and/or are not driven to get up to the full operational temperature they can toss phantom CEL. Had a few over the years where I check the code, know it's not real and clear it never to be seen again.

So take it out and "drive it like it's stolen" a few more times which should hopefully clear out the entire system. As I mentioned Cataclean unfortunately it may require more driving than what the vehicle may get just something to mindful of if adding anything to fuel.
Thank you.
I told my GF that (as I kinda suspected that too) and she thinks Im just lazy. Sometimes you just never win :)

Im going to take it out again and "drive it like it's stolen" (lol!) and see how it goes :)

If it does come back, I guess I refuse to take it to a shop. I will pick up some MAP gas and get very serious with this beast :)
 

2007LucerneCXL

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The CEL's usually show up right after I get my notice of the upcoming emissions test. I think the vehicle is just keeping me on my toes or ONstar operations was bored that day and having a little fun lol.
 

2007LucerneCXL

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While older low mileage vehicles are a great find, elderly Buick owners usually over maintain their vehicle some times because of unscrupulous shops, other than oil most other fluids are "factory fresh" as they haven't hit the mileage to be changed.

Most manufacturers will list recommended changes with mileage or years but even on the forum it's a topic by a entire range of age groups that is debated.
 

Buickguy123

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Yep. My Mom :) Sat in the garage for most of its life.

This car is the poster child of "Little old lady only drove it on Sundays and to the grocery store".
A dealer in GA had one a few months?ago with just 28000 miles. Red tan leather interior. Like new LOL. Enjoy!
 

century61

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Well, I have been away for a while. Sorry I have not replied. This gets good though.

I ran a scanner on the 2007 Lucerne and watched the O2 sensors after clearing the error P0420 the next day. I ran the car around town and the error never came back. Graphs show the O2 sensors working fine. I figure that because my Mother never really warmed this thing up over the years there is carbon build up that affected either the sensors or the cat. So, I am going to get some 'Cat Cleaner' and run it thru a tank of gas. I figure this will probably clean things up. Now, Lets tie this in to my car which is the 2008 Buick Lucerne. This is where it gets good.

I have been complaining about hard shifts with the transmission and I kept wanting to take it in to the transmission shop and get this sorted out. I just never had the time. So, Over a few years I just drove it slow - never pushed it very hard. Well, Yesterday I decided to take it in. The owner of the shop is a client of mine. He checked it out and called me and said there is nothing wrong with the transmission. I had a broken motor mount. WTF? So, I had him fix that. I picked it up today and it ran fantastic. Im thinking, "Gee, I got out pretty cheap on something finally!". Well, Just before I got home my check engine light came on: P0420.

Im hoping that I just have carbon build up like my Mother's car since I was so gingerly with it. I will run some cat cleaner thru that and see if it clears. Otherwise, I might be putting in a new cat. I have 151,000 on it.

So, Im being harassed by a P0420 error - both cars! Go figure? Well, life goes on....
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century61

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2008 Buick Lucerne 3.8 liter
I ordered up a few bottles of cat clean. They arrive today and tomorrow (3 bottles). I will update this after running the cars a while.

If I have to I will probably replace the cat on the 2008 model. Ill use my "Buick Stimulus Check" (from gov) and replace it myself. It will be an interesting project to do. A few weeks back, I bought one of those inductor heaters - I bet that will come in handy if I have to pull the cat. Kinda excited to use it :) .

I want to thank everyone for replying here. I guess I should be thankful that my transmission is fine and it was just the engine mount. I am beating myself up for not catching that and getting too focused on it being a transmission problem. After this, I would probably tell everyone that seems to have a hard shift from the transmission that they better check their engine/trans. mounts before anything else. Although it was not that expensive to have the shop do it - I just feel I should have caught that. Makes me feel stupid.
 
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