I have taken great pride in being able to figure out what is wrong with my cars on my own and, in the past have almost always been 100% correct on the diagnosis. While I often fix them myself, at times, I decide the fix is either over my head or just not something I want to tackle. Recently, I "self diagnosed" an issue on my 2002 Suburban that ended up being way off - and cost me some $. I share only to laugh at myself and, perhaps, prevent a similar mistake.
In about October I started hearing a grinding noise coming from the front of the motor. I suspected it was the air conditioning compressor as the noise was in that area and it is a known issue on Chevy trucks so I removed the serpentine belt and started the motor - note that there are 2 belts on the Suburban - one that is A/C only. With only the A/C belt on the noise was still there, so I was pretty certain that was the problem. Here is where I made my mistake - I put the serpentine belt back on but I cut a corner and just cut the belt on the A/C - noise went away. Conclusion - needs a new A/C compressor. I drove it through the winter this way with no issues
Fast forward to a couople of weeks ago. I take the Suburban to a shop and tell them it needs a new A/C compressor. They replace the compressor as instructed and on my way home the sounds comes back. I am like WTF? I climb under the truck while it is running - there is a freakin tensioner pulley on the bottom that I did not even know was there. If I had taken the belt off the right way I would have known that of course. The pulley is screeching. I go to Napa buy the 25.00 part and by the time I get home the belt is shredded. It took me < 30 mins to replace the pulley.
I suppose I just chalk it up to a learning experience and remember all the money I have saved over the years doing it myself.
tl:dr version - I screwed up diagnosing a problem on my car and it cost me money - don't do that