Polaris Sportsman 500 electrical issues kills running engine??
 

I have a 2009 Polaris Sportsman 500 that isn't running properly. I don't run the machine very often, in fact it can sit for 2 months without ever being started. In the last 6 months, it has been sporadically just shutting down while running it under normal operations, high gear @ 10-15mph not under any load. Sometimes it will run without issue for several hours. 2 weeks ago, I did a COMPLETE SERVICE on the machine (100% all fluids & filters replaced, spark plug, fuel filter...everything). What is happening that's so perplexing is that the machine will start blinking the electronic screen in speedo then just shut off. The battery is original but holding a 13.4 - 13.8 charge no problem. It doesn't seem to act like a bad battery symptom, but before I replace that, I'd like to know if anyone has an idea of what else to check. All fuses are good and do not blow. All electric accessories work fine, (i.e. hand grip warmer, warning strobe lights, stock lights) while at idle. Also, worth noting, the machine starts strong, idles smooth and revs smooth. Any ideas as to why this is occurring?

does it show a code? as long as the connections are good and not corroded I doubt it would be the battery as you mentioned it shows good voltage. what does it show for voltage when its running at say 1/4 or less throttle to make sure its not over charging?

Battery voltage reads a steady 14.8v @ idle (1200 rpm), 2500, 3500 & 5000 rpms. Battery is old (09/20018) and will be changed. I used the owner's manual to try to see if there are any codes, but I can't seem to get it to enter the "mode". Manual says to put it in Park, turn on ignition, then cycle the key off then on 3 times in less than 5 seconds. Then screen should display "WAIT", then blink codes....etc. I tried that procedure numerous times but it doesn't ever show "WAIT". Could that be because the check engine light is not displaying during normal operation, therefore not showing any codes?

Most of my online research, including this site, shows that it is most likely the ECU, as the late OPT calls it, or the ECM as many others call it. Many individuals describe the "chaotic" flashing of the screen as one of the early symptoms of a failing ECU. Some folks describe the machine working fine 1 day and then absolutely nothing the next. Any knowledge on how to test the ECU to be sure before I guess and order a replacement ECU?

well that was going to be my guess as it seems to be hit and miss as having a bad ecu or on its way out. if your battery is holding its charge and not being over charged then it's most likely fine.but it is 10 years old so that would be your call.

Picked up a new battery today and will run machine tomorrow to see if issue disappears or continues. Thanks.

Make sure the plug going in to your engine run switch is fully plugged in. If it's bad connections or dirty it can cause issues. Mine had a bad clip and game out one say killing the engine

Update on electrical issues. Stopped in and spoke with my local Polaris dealer and described my issue and he immediately jumped in and said "battery. Replace your battery. It's a 9 yr old battery, so you'll need to replace it anyway." Well, my plan was to replace it anyway, so I installed the new battery AND found all the grounds to chassis connections and pulled them and cleaned them with a wire wheel to remove any corrosion. So far I've put about 4 hours on the machine without any signs of the electrical issues continuing.
I guess it should serve me to remember to start at the basics when troubleshooting. I was sure it was a failing ECM/ECU.

Did you ever load test the battery? The bad ECM/ECU/brain box problem was mainly with earlier models, 2004-2006, or something like that.