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Hi, I'm new to this forum but my Enclave is high mileage (150K) and I am having trouble getting a few things corrected.
Ever since I bought the car from a private seller used in AZ it has consistently thrown the P0420 and P0430 Catalytic Bank 1 and 2 above thresh hold codes. The car ran fine until i started messing with it to eliminate those codes. I jumped the gun and replaced the Cats with a pair of generics from e-bay which actually shortened the time it took to set the codes. I also tried a couple different oil and gas additives to no avail. As a matter of fact, the engine protested by misfiring when adding some of these.
So, I had the oil filter and oil changed to the correct 5W 30 and we drove the car back to Wisconsin. After about 600 miles of trouble free driving the car started misfiring at 70MPH in 6th gear going up any hills on the road. I ended up driving it back the rest of the way manually, shifting to 5th, or even 4th gear whenever we encountered any hills. The car seemed to run fine around town but I took it in to my mechanic who analysed it and repaced all the plugs, 1 coil, one cat gasket and another oil and filter change and had the codes cleared.
After about 15-20 miles the codes were back. They felt the cats and 02 sensors were ok and suggested I go to a Buick dealership to see if there was a software update to loosen the 02 sensor values for my VIN and high mileage.
The Buick Service Department told me they could not tell by the VIN and I had to bring the car in and have it checked by a tech on the car itself.
I made an appointment for Friday and brought it in to have it checked for any Cat or 02 sensor related updates.
They called me and said that the 02 sensors were bad and needed to be replaced with genuine GM parts. Even though the price was outrageous, I agreed. The tech called me and told me they did find and applied 2 updates, one for the instrument cluster and one for the Fuel Pump Control Module and that they had tested it and the problem was solved. I picked up the car to find it had been test run about 65 miles till the gas was almost gone. So I quickly put in some gas and drove it home and out for supper. No problems no CEL etc.
Saturday morning we were to go to a graduation about 2 hours away. My wife started the car and it was idling when I came out. The car was idling roughly spewing toxic gas smelling white/grey smoke out of both exhaust pipes. We tried everything to get it to stop, but it would not run right and we could not drive it. I was able to retrieve 13 Power train error codes dealing with fuel mixture, pressure and stuck items from the OBDII and record them. I tried calling the Dealership, but they are close for the weekend. So I thought I would disconnect the battery for 20-30 minutes. That seems to have reset the ECM temporarily, but I don't feel save driving it and I am not sure as to how to approach the dealer. Should I ask them to put the old software back in, or could the low fuel have caused something to get stuck in the fuel control? If anyone has had a similar experience with a good outcome I would appreciate hearing about it.
Thanks
 

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Do you know if they did any work related to cleaning up the Carbon? (that usually causes lots of white smoke).... but right after the work is done.

But I would suspect carbon buildup was causing the misfires/
 

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Dropped the car off at the dealership and asked them to please set the FPCM software back to where it was. All the codes that were thrown were related to fuel rail side. NEVER had a fuel related code trip before. They kept it for 3 days and called to tell me they started it every morning and that it is noisy/rattling in the morning and that it will need a new timing chain to solve the problem!!! Is it at all possible for a 150K mile car to develop 02 sensor problems, Fuel pressure problems and timing chain problems just when I take it into a dealership? I don't believe it! The car was running fine after replacing a coil and the spark plugs. We drove it cross country. All I wanted was to see if there was a software fix for the P0420 and P0430 Cat codes. Instead they mess with the fuel system software and are now telling me it can't be reversed. IS THIS TRUE? And now they are telling me basically I need a new engine.I don't know where to turn. Is there a Buick rep in this forum that can give me some guidance??
 
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