I just purchased a 2014 Prius C1 with only 49000 miles on it... A Friend told me to vacuum the Hybrid Fan Filter out... I had to take the Fan cover off... itv was full of lent... Then I put everything back together... and I noticed I could hear the fan hitting the edge of something? So I took it all apart and put back together... Then the Fan work great... No problems... Now this morning I have a CHECK HYBRID SYSTEM stop the vehicle in a safe place... and the fan isn't moving? I'm not driving it... Any ideas?
With over 10 years of age there isn't likely to be much life lefft in that battery, especially if you found the fan full of fuzz. It is worth re-checking the fan and ductwork, but it's probably time to use a scan tool to find out exactly what the car is complaining about. The Autel AP200 and AP2500 are good lower-cost tools that are capable of talking to every system in the Prius c. Many tools will only scan the fuel injection/ignition system and ignore any problems that may exist in the hybrid works.
It's a car that was only driven 5K miles a year, more than likely short hops with a clogged cooling fan intake. I hate to say it, but the battery may be toast. Pull the codes to see what's up.... hope this helps.... FWIW; the coolant needs to be changes and the brake fluid system needs to be flushed out. At a minimum they both need to be tested.
Did you by any chance pull the "service plug", the orange plastic gizmo you remove to isolate the battery? If so, maybe not reinstalled fully??