My neighbor asked me to get his Foreman running. I generally have no problem with this kind of stuff. The quad does a lot of sitting. I took off the carb, cleaned it, then reinstalled it. It would start but not rev up completely. So I took the carb off and cleaned it again. There was no change. I looked at the tps and there is a wire that goes from the harness to the sender with a black box in the line. On one of the connectors of the wire, it had wire showing. So I added some solder and heat shrinked the wire. I get continuity through the plugs. Another thing to mention is that it will Rev up if the choke is pulled, to me, indicating a lean condition. The spark plug is new. Today I noticed a code where it shows -- and ESP D1D2. It stays solid then blinks four times and repeats. What does this code indicate? What could be the issue? is a video showing the code.

 

Strange it rather looks like a code 14 and there isn't a code 14, so must be code 4, gear position switch fault, I would assume that is the one under the lever, may be why you get D1, D2 up as well. Never worked on a 500 ES, we wouldn't even sell 500 manual shifts for a while as they ALL started jumping out of gear within 2 years. This fault was "fixed" quietly by Honda in 2007.