When I bought my used 2001 MDX last year the rear fans were dead. There is a good thread somewhere on this forum that helped me fix mine. The net of it is there is a control board for the fan that is located in the console area. I think it's a thermal link failure on the board that cripples the fan. A good electronics person can fix the link but I did not attempt that. You have to pull quite a bit of the covers on the console (driver side) to get to the control board. I talked my dealer into buying me the part I needed (about $125 from Honda dealer) and that solved it. Also need to clean a screen-like round filter that clogs with dust - located front of console area. It's visible when dis-assembly of console gets far enough along. Try searching for the thread if you have not fixed your MDX yet.