Originally Posted by KyBucks10

The one you have labeled as #2 is the sensor for the computer. The one on the block just above the oil filter is the one for the gauge. Ive changed both of mine out. The one you have labeled as #1, I have no idea what that is. Im not sure if my truck even has that?? I am interested now, and want to go look. Itll have to wait until tomorrow, though!

I will point this out, though. My truck had the check engine light on ever since I bought it. I knew what was wrong though. I had almost no exhaust, so my o2 sensor wasn't reading properly. Well one day just for the heck of it, I went and had it scanned. To my very surprise, I was throwing out 5 codes instead of the one. I did a little research and figured out that since I replace my thermostat housing and never replaced the sensor in it (your #2. My new housing came with a plug in its place) I threw out 4 more codes, all of which were fixed once I put that sensor back in.