Unfortunately there is no quick answer to this. There are many reasons the REP light will come on and some are computer related and some are electrical. The codes are important as you see in the prior post, it can be a myriad of things. If you have a multimeter, you should check the voltages first make sure the 5 volt is operating from your fan clutch to the throttle body and pedal. You should at least know if something is not getting power before you have to go to higher costs of diagnostic labor.
My Envoy had no throttle response or control and started without any warning. Came out one morning to go to work and boom, it was on and running like it was on 3 cylinders. I changed the throttle body, pedal, and PCM and that did not fix the problem. I pulled harnesses and checked wires. I checked fuses and power from the fuse box to the PCM. I could not find anything that made it work. When none of those worked, I almost replaced the throttle body pigtail but could not put that kind of money into it and still not know if it was going to work. I ended up taking mine to a dealer and nearly $800 later, I had a bad (original) PCM and the throttle body pigtail needed to be replaced. I have 5500 miles on it since then and no problems. If you have someone with dealer level equipment, they may point you in the right direction if you are not electrically inclined.
There are some pretty good people here that can help walk you through some of that testing if you need the assistance. It can get rather expensive if you start throwing parts and still have to have a portion of the wiring harness replaced anyway.
Good Luck.