Doesn't Switch Back to EV Mode

EV mode in Summer is more limited due to air conditioning drain on system.

Low tire pressure is a common source of bad MPG and having your 100K mile tune up, which is an easy DIY of changing spark plugs, air filters and cleaning throttle body and mass air flow sensor, and oil change, 12v battery health, etc... Please follow up with how it all works out.

 

you may have a clogged egr circuit, your mileage is ripe for it. hopefully, not a blown head gasket yet.

when mine wouldn't shut off, i did an italian tune up, and it worked. but i suspect i will have to clean the egr if i keep it long enough

 

I came here to start this exact thread, so curious to know what you find out.
I have a 2014 with only 52K miles.
Noticing the same symptoms of car not switching over to EV when it normally would - and further seems to struggle with power in situations when it might ordinarily be getting an EV assist.
I have not so far noticed a big drop in MPG ( I usually look at tank average).
There are trips where it seems to behave "as normal," and other trips where EV never seems to engage at all.
Tires are properly inflated.
I recently went to the dealership for a software recall notice and had them scan all trouble codes and do multi-point visual inspection and road test, but they found no issues.
On the return home, after I pulled into my driveway, the car took more than 5 1/2 minutes to switch from ICE to EV after I put it in Park. This normally happens within seconds. Outside temp was only 83F. HV battery temp may have been hotter, but it didn't "seem" like it would have been at an unreasonably (or unusual) hot temp, relative to my experience with the car.

 

I just figured I would update with new info, even though there is nothing revelatory. still don't know whether anything is actually "wrong," but am interested enough to keep reading things and poking around.
decided it was time for another hv battery fan cleaning, since the last one was a few years ago. followed along again, step by step, with @NutzAboutBolts fantastic video.
really not much dirt in the fam - about same as before. some fine dust. I did use brake cleaner this time, but I don't think I would advise it, or use it again. that stuff is too harsh and even when I was careful spraying it, it pooled up in the bottom of the fan, and I had to drain it out, and it got the foam insulation lining wet, and I thought that's probably not good for it. so, next time, I'll just stick to damp Q-tips.
(it really didn't clean it better anyway).
the lint screen was the dirtiest thing, so I blew that out with some compressed air.
I also got an OBD2 scanner thing, and the dr Prius app.
did the lifetime expectancy test on the battery and saw it has 50.22% capacity left, which though considered "fair," sort of surprised me since it has only 52K miles on it. it would seem that I would need a new HV battery around 100K miles if that extrapolated linearly. not sure if it does. most other people seem to go much further on a battery.
I scanned for codes and nothing came up, and I decided to go for a drive with the scanner plugged in, and the app interface up.
I did a round trip in 2 10-minute segments, up a hill and back down, parking in-between.
I didn't understand much of what I saw - modules 5, 6 and 8 did not show any bars for "Internal resistance," until about the end of the first leg of my round trip. and at the very end of the trip, almost all bars for Internal Resistance turned off, except a few of them.
a few times, while braking, I saw the Pack Voltage indicator go red.
the fields that mostly held my interest were the Battery Temp fields. Battery Temp 2 stayed the highest consistently.
when I started the trip, the car was cold - batt temp 2 was in the low 80s F
by the end of leg A, it had risen to around mid 90s
when I came back to the car (after a 15 minute trip buying groceries - it was parked in the sun), batt temp 2 was around 111F, and quickly rose while driving to around 117F, but never went over.
it's possible that the days I noticed the lack of EV switchover the temps were just too hot. not sure.
only other notable thing was the car started very rough today, when it was cold. the whole initial ICE engine startup (until it switched back to idle EV), it was shuddering a bit.

 

surprise battery wasn’t checked if it’s still under warranty.

 

There is no sence in NOT cleaning the cooler along with everything else.
If it's blocked, you'll still have a problem.