It started with loss of power, poor mileage, smoking tail pipe, lights and bells going off. I took the car to the local GMC dealer where I bought it for a diagnostic check. They gladly said they could fix it for $4,600.00 and gave me a 2 page list of the parts needed. I contacted a mechanic friend who told me which parts to order. Spent $237.00 for a brake light switch, evap canister vent valve, oil pressure switch, wheel spin speed sensor, 2 O2 upstream sensors, plugs and wires.

He put the parts on for $300.00, cleared all the codes and the car ran fine until a week ago. While going down the highway, all of a sudden everything started coming back again just like before.

Going to a parts store for diagnostics is a waste of time even though it is usually free. Their dinky scan tools will not pick up the real cause or code for what is really happening. Apparently all this is tied together somehow. You will have to take the vehicle somewhere that can give you a COMPLETE diagnostic scan.

This problem shows up as several different things with several different fixes. If you search the internet you will see that there are hundreds of complaints for this or one of the associated problems. Time after time you read about someone who managed to get it fixed only to have go out again in a short time.

I have talked to 3 SERVICE MANAGERS from 3 different dealers and was told that they nor GMC knew what causes this problem.

I WILL NEVER HAVE ANOTHER GMC PRODUCT!!! There should have been a class action suit about this.

Oh well, screwed again by another of Americas largest companies!

Update from Aug 7, 2018: OK, so I have a complete diagnostic scan again. Comes up as a misfire on cylinder 6. Change the coil pack, wire and plug. Keep getting the same thing. So I have a compression check done on cylinder 6 and get low pressure reading. Have the guy pull the valve cover to see if there is a broken valve spring and find out that the lobe is worn off the cam. So now I have to replace the cam or put in another engine. So my advice to you if you have one of these and it runs good, SELL IT NOW!!

Update from Aug 8, 2018: After much research I have discovered that my Yukon with 5.3 v8 has the "Active Fuel Management" type engine that has been nothing but problems for many owners. The 2007 Yukon is listed as the worst. AFM is where the engine changes from a V8 to V4 to conserve fuel. Apparently what this does is gums up the valves and lifters causing them to stick which causes misfires which I have. I have read several forums about possible fixes for this which include cleaners like Seafoam in the crankcase to clean the valves and lifters. This may have to be done 2 or 3 times in succession. I'm going to try it before I do a tear down.

I have had my Yukon for 6 years. It has been a great vehicle all except for the stability track control. On my way home from church driving with my 2 and 8 year old it loses power and power is reduced while driving on the highway. Pulled over, turned it off and waited. Only to have it to this to me again just a few miles down the road. This time not only did it reduce power but I had no power steering. After I wait for about 5 minutes I could restart and drive again. I made it to my neighbor before it did it again and it has been parked since.