I have a 2005 Yukon and have been fighting a Check Engine light for a while. I don't have to codes available at this time but I will post them if need be. The codes show as O2 sensors "Bank 1" and another for the MAS. I've replaced both pre and post CAT drivers side O2 sensors and cleaned the gunky throttle body. I cleaned the throttle body first and the codes went away for about 100 miles. I then replaced the O2 sensors, the codes went away for about 15 miles. Any insight?

 

Without all the codes, it's hard to point you in the right direction.

Also a 2005 GMC Yukon would most likely have a 5.3L engine.

8th Digit of the Vin code Is for the engine designation. If its a 5.3L, it will either be a T or Z.

 

Yes that was my bad. Typo. It is the 5.3 I'll post the codes tomorrow.