I have a 2004 Outlander 400 that has sat in the garage for 3 months. I charged the battery prior to starting and added fresh gas. The battery would run gauges and headlights which appeared bright but would not engage starter. I jump started the quad and it started surprisingly easily. I allowed the quad to idle for several minutes before attempting to ride. When I attempted to rev the engine it would not rev very high and ran much like it does when the rev limiter kicks in when in reverse. I looked at the display and it was scrolling between the hour meter and a 'Fail' message. I turned the quad off. With the engine off and the ignition switch in the on position there is no 'Fail' message. When the quad is started (jump started) the message appears and the engine idles smoothly but will not rev.
I know the battery needs replacing. Could this be causing the problem? I would suspect the carburetor but the quad starts and runs smoothly.

 

Replaced battery. Starts, idles and runs fine.

 

SM, I might not be an expert but I do have the same quad as yours. 1 question: Do you have the updated voltage regulator? When the 03 - 06 400s displayed "fail", it often meant the VR was about to implode & cause all kinds of havoc including frying your battery among other nasty things. An easy test: Check the voltage to your battery while it's running, warmed up and displaying the "fail" message, if it does at all. (A new battery will handle the load of a failed VR and not display "fail" -- for a short while.) Anything 15 volts and up is a bad thing -mine was pushing 20 while idling - not good. Bomb/Can-Am has a service bulletin on this. If you're still not convinced, stop & check the temp of the VR after a short ride. If it cooks your fingers, I'm willing to bet it won't last long or it's already fried. The new ones run way cooler. Also, if your battery starts whistling like a tea kettle at any point, that's also bad news. Of course, this means you'll be on the hook for the updated harness & 2 plug VR. There are also 3rd party comps that build these for cheaper but I don't know if they're any better. Just thought I'd give you a heads-up. It could save your new battery....