How can I determine whether ECM has been replaced?

The first thing I would check is your spark plug. Make sure you have the correct plug. Make sure the plug is not fouled ( excessively wet or burnt looking). If the plug is questionable replace it. Next make sure you have good spark. TIP- while drake plug is connected to the plug wire hold to cylinder head while cranking engine over (make sure the kill switch is set to run). Once you have determined good spark and the condition still exists, check your fuel quality. Look for water is fuel and/or if the fuel is old and varnished. If the fuel is questionable drain fuel system and replace with good fresh fuel. (91 octane or higher) If fuel quality is determined bad, remove the carburetor and disassemble. Clean jets, fuel bowl and blow out passages with compressed air. NOTE- wear safety glasses and rubber gloves.

Unless there is a factory notice/recall, the chance is equal one will fail before the other... Sounds like its time to have it professionally checked, being a "parts replacer" type of mechanic can be VERY expensive. You might get lucky and the problem is cured by the first part you replace or it could be NONE of the above..(broken wire, bad connection..etc..).. and then you spend untold $$$$ and not fix it!!

If you have changed your thermostat then i would check and see if your hoses are not pinched also see if your radiator is plugged so it does not flow properly. Is there a water pump that needs replacing. I am not sure what all is involved but a few things to look at.

Your control module is eqaulivont to a ecm in your car, its the brains for all operations.

code p 500 refers to vehicle speed sensor(VSS)--circuit malfunction===causes ---wiring--VSS---ECM check wiring
replace VSS

2011 Polaris Rzr ranger there is a fuse in line under the floor pan below the battery that gets corroded on the main wiring harness removed and relocated above the backseat try that you could buy one at Napa for under $10 try it I had the same problem with mine good luck

It sounds like you have a bad starter motor.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/dave_fb2c45146b845cea

I suspect that you will need the sender unit replaced. Check to make sure that it can be repaired under your warranty or if there has been a recall on your model.

You need to first determine whether the problem is fuel or electrical. Remove the sparkplug and pour in a small quantity of gas. Replace sparkplug and high tension lead. Crank it over. If it does start and run a bit then your problem is fuel and not electrical. If it does not fire and the sparkplug is wet, then start be replacing the sparkplug with a new one.

Write a letter addressed to the President of Polaris explaining the events leading to replacement. Keep the letter open without demands. This may result in a positive solution from partial o full reimbursement.