2010 55K Miles Sluggish Transmission Whine

Hi᠎,

You have a car with a continuously-variable transmission and no shifts ever. So I am sure you are noticing something, but it won't be anything to do with whining "between gears" or "shifting as soon as it should".

Is your traction battery original? It generally chips in some power for acceleration, like when you're doing those 55 to 85 maneuvers. If the battery is older and not contributing as much, the engine has to pick up the slack, and the engine will turn higher RPM to do so.

There would be nothing very unusual about that in an older Prius III if it's on the original battery.

 

Just for giggles try changing the transaxle fluid? Dealership should not charge much more than $100, it is just a drain and fill. If DIY'ing or using an imdependent mechanic, you'll need:

4 quarts/litres of Toyota ATF-WS fluid (use nothing else, and only use from freshly opened bottles)
2 replacement washers for the fill/drain bolts
ratchet wrench (very preferably long handled) with 10 mm allen key style bit
Torque wrench (torque value for both fill and drain bolts is 29 foot pounds)
Some method to get fluid in: a funnel with 3 foot hose extension (keep hose od to 5/8" or less) is simplest and most trouble free. Or a pump gizmo
Drain pan of some sort, obviously

Tips:

The car should be level during the fill process. Typically raising the whole car and levelling it (safely) for the duration of the drain/fill is simplest.

Break loose the fill bolt first, just in case they're stubborn.

Fill till the fluid starts coming back out, and the level is correct.

If filling from above, the first three quarts/litres can be poured relatively quickly. Then go slower, pouring say 100 mm at a time. Around 3.5 quarts/litres it'll start coming back out, and you're done.

 

It could have dragging brakes, worn wheel bearings or, as suggested, reduced battery power contribution. Any of which can cause the engine to rev higher. Much like going up a steep hill, the engine will rev up as the transaxle selects a hill climbing gear ratio. When the load reduces or the battery can contribute more, the Continuously Variable Transmission will then change the gear ratio again and the engine will reduce its rpm.

What's Different About the CVT Transmission? - Toyota Canada

 

In the Prius transmission, the transmission fluid doesn't do anything but lubricate, and slosh some heat away. In other types of transmission, it can be involved various ways in carrying power.

Because of that, for the symptoms here, I wouldn't expect to learn a lot from a fluid change. It wouldn't hurt anything (usual assumptions about competence, etc., go here), but just be a certain amount of time and effort going in a sideways direction from the reported symptoms.

 

Hybrids behave strangely when the 12 volt battery is weak.

With my old hybrid I turn everything off when the engine is not running.

when it gets a bit cooler, see if the engine still does what it's doing with the A/C turned down some or turned off.

 

I would follow that link but with a small grain of salt kept on hand.

It does a good job of explaining what's good about a continuously variable transmission in general terms.

But as it goes beyond that, it is concentrating on CVTs that operate mechanically. While the transmission in a Prius is also continuously variable, the way it is built is completely different (using two electric motors, a small handful of gears, and a computer), and so a lot of the specific details at that link are a bit off-topic for the tranny in a Prius.

 

AZ heat brings an extra set of variables to Prius behavior, that are unique to your area. ie: in cooler climates it's usually recommended to drive the car more than once a week. (I think only driving the car once a week in that kind of heat has actually helped the traction pack battery stay usable for 11 years). Good news next week Sept 19th thru the 26 and it's forecast to be high 70's at around 6am and the high 60's the next week around the same time.
My experiment for you (because I don't have real world experience in those kinds of temperatures) is to drive your Prius for around 20 miles early in the mornings once a week between your normal drive and see if that helps. Good news is 55.000 miles in a 2010 is really low mileage, although 11 years in AZ heat has probably not been to friendly to the cars traction pack, even though the pack has only been exposed to those temps once a week or so.

 

Both, Hybrid Assistant and DrPrius apps for android phones along with an inexpensive elm327 bluetooth adapater like a panlong have a paid option to enable the traction pack health test within the free apps options. around $20 + or -

 

Yes. the Panlong Bluetooth ODB2 ODBll Car Diagnostic Scanner Check Engine Light for Android -Compatible with Torque Pro $12.99 item model number PL-B02 is the same as a the adapter the developer of DrPrius used while making the app. - more info here Hybrid battery diagnostic and repair tool for Toyota and Lexus

Here is another for $32 at amazon that works with both Android and iOS phones
Vgate iCar Pro Bluetooth 4.0 (BLE) OBD2 Fault Code Reader OBDII Code Scanner Car Check Engine Light for iOS/Android

Neither Hyhrid Assistant nor DrPrius apps work with Honda.
Both Panlong and Vgate iCar adaptes will work with Honda and perhaps the Torque app will as well. But Honda has kept their ODB2 signals/protocol data proprietary and there is limited support for honda diagnostics at a reasonable price, to the best of my knowledge. Maybe you'll have better luck finding what you need for your honda than I've had finding help for my old honda hybrid.

 

If your regular use of the car is once or twice weekly consider getting a smart charger, hooked up steady. That typically requires secure parking with electrical outlet though.

If the hybrid battery charge indicator is sometimes showing just one bar, I don’t think that’s normal, could be failing. Typically should never have less than two bars.