Real old post I know, but did you ever solve the shifting problem?  My 2015 is the same.  It seemed to get better for a while, but now its gotten pretty bad again.  Not sure what would affect it or why it would change.

Looks Nice!

Just to clarify, all the other electronics seem to work when the key is on, but it will not crank?  or is it cranking but won't start?  Does the kill switch seem to work?  If it is activated it should make the efi light on the display come on. At least on my older model it does.  So if the kill switch is shorting it may show that.  Also, make sure your break switch is working. Do the brake lights come on? Can you hear the relay click when you pull the brake?
Also, check your main fuse. If power is not even getting to the solenoid now it would probably be a blown main fuse. Mine is under the seat next to the solenoid/start relay.

I have not checked an owners manual but it probably lists a recommendation.  I have always just listened to the RPMs and throttle feel in low range.  I try not to push mine past the RPM range I commonly hear in high range(my normal trail riding). 

Well, I think I finally found my problem. After hours of testing and searching for wiring issues, I still didn't want to pull the trigger and order a new ECU, so I decided to open up the current one and see if I could see any issues to verify if it's bad or compromised.  I could see there was some dirt way up in the connector suggesting water had been in there, and also I could see a spot around the outside of the shell where no sealant was visible, meaning Bosch didn't get it sealed up well.  So I warmed it up with a heat gun to soften the sealant and pried it open(gently).  See pics. I found water, corrosion, burned connector pins, etc.  So I will be replacing this ECU and will update if that is the end of my issues. Hopefully before new years. 

Had time for a little more testing. CPS tests out fine.  The resistance is 1K ohm like it should be, and it produced over 2V during cranking (I think it was 4-6V).  The Speed Sensor seems bad though.  It should alternate between 0 and 12V, but I'm only getting .2 - .4 volts off the signal pin when powered and I put a bolt head up to the tip of the sensor. When installed it does not change or alternate as I turn the back wheels(very slowly). There is power going to the connector, so I'm thinking I need a speed sensor.  But, even with the speed sensor unplugged, there is no change in any of the other symptoms. The fuel pump still runs and start button does nothing. 
I also tried to test the injector, and Im getting about 6V DC at the connector with the key on, but the injector does not spray.  I know it should be a pulse from the ECU, but I don't have a light to see if its pulsing. I also saw in the service manual that the Idle Air Valve is connected to the fuel pump relay, so I'm going to try and test that next, but not sure what I can test other than its resistance.

Thanks NMK !  I will try testing this stuff, hopefully tonight. I have no injector spray and no spark, so sounding like possibly the CPS, or its wiring. I have tested the kill swich at the end of its cable, but I didn't know the colors or positions in the connector, but found some that were making and breaking cleanly, so assuming its working, but I'll check that again too.

Still no progress on this.  I tested and swapped the aux relay and it was fine, no change. Did pull the injector, and it is not spraying when the fuel pump runs, so assuming the injector is ok.  I read in an automotive forum that if the crank position sensor is bad, and sending signal when it shouldn't, that can be telling the ECU to send fuel, but then I would think the injector would be spraying.  And that shouldn't kill the spark either I wouldn't think.  Anyway, will try to test the CPS and speed sensors tonight.  Really don't want to drop $400 on an ECU without knowing.   

I searched on here for instructions on reading the codes, but didn't find any clear instructions for machines that only have the 3 wire. Does anyone have a link to a thread that has been successful?

Did you check the AUX relay(s)? And what exactly is the fuel pressure?

No, I didn't check the Aux relays yet, will do.  Fuel pressure is 40psi exactly.

@Doug80638, thanks maybe I'll look into making my own PDA.  Unfortunately my nearest dealer is over an hour away, so would be a while before I can get down there.

I had time to do some more troubleshooting before deer hunting this weekend.  Put the new fuel pump in and no change.  Runs steady when key is on.  Builds and holds pressure. Does not leak down.
Jumped solenoid and engine cranks fine.
Start button still dead, so continuity tested that at the end of the cable and start switch and kill switch work fine. Also when kill switch enganged, the EFI trouble light comes on, so it is being acknowledged by the ECU).
Checked spark while cranking the motor, and no spark. This is while the fuel pump is running.

At a loss. Beginning to think the ECU is at fault as it controls the fuel pump and the ignition system. Not sure what other inputs might cause these issues.

Any ideas welcome!

Will it turn over when you jump the starter solenoid?

Unplugged the fuel pump last night and jumped the solenoid and yes it cranks fine. Got the pod loose and can't find any loose connectors or bad wires so far.  Have to get the tank off to get to the injector. Maybe tonight.

Will it turn over when you jump the starter solenoid?

Have not tried yet.  When I was unhooking the fuel pressure gauge, the plastic elbow fitting on the top of the fuel pump broke, so now I can't do anything without spraying fuel.  Looking for a new elbow fitting and waiting on a new fuel pump from Amazon.

Looking for some help. My 2015 CF 500 HO ran fine. The next day I went to start it, and the fuel pump just runs.  Does not prime then shut off. The start button does nothing. Will not crank.  There is no fuel leaking out so not sure why the pump doesnt stop running.  I bought a new fuel pump relay but no change, and tested the fuel pressure and it is exactly 40psi when the pump is running.  But either way I think the engine should crank over. I checked the main fuse under the seat and is good. Battery is fully charged. Any ideas?  **Edit, not getting any error lights on the display. Thanks!

Yea, Im trying to stay upbeat about it so my daughter doesn't feel bad.  Hoping I can revive it enough to last through deer season just to drag a couple deer. Then I can tear it down over winter.  It only has 600 miles on it is the sad part.  It came from Polaris where it was a comparison test machine, and then sat in their test fleet for 5 years.  I see there is a crate motor available but its $3.5K. I'm only into this one for $2K (part of a $6K package deal with a Hisun that I got $4K back from). So I still wont be out of line if I put parts or a motor in it.  We will see. Im just not very familiar with these modern machines with OHVs and EFI and EPS systems.  Never to old to learn though.

If it does that regardless of the charger on, it could very well be a faulty key switch, or something shorting the dash display wiring. I would test the switch first, then start under the display and work back from there.