burning smell uphill?

Probably lost the inverter coolant pump. Put the car in ready and open the Black Cap on the inverter coolant reservoir and with a flashlight look inside the fluid should look like it’s boiling reflecting good coolant flow,

Or the engine is very low on oil. Both of these require opening the hood though.

 

On cars in the past I've got smells after a hill-climb (well a mountain climb) that were likely from undercoat that sprayed onto the exhaust. Still, @edthefox5 's suggestions are more serious, should be checked first.

 

All fluids should be checked and monitored until you find the source of the problem.
Have you ever checked the coolant by removing the radiator cap instead of just the overflow tank?

 

So I was crossing a major hill (Alps in Europe) at high speed (about 80mph) and got burning smell too. Not noticeable when driving, but when we stopped right after a long fast uphill drive, the A/C pulled the smell in and it made a noticeable light fog inside. Gone away in a few moments after we rolled down the windows. I walked around the car and didn't notice anything odd when outside.

Had the car checked at authorized Toyota dealer and they found nothing wrong with the car. It might have been just some vax or other residues burning off when ICE got really hot as it normally does not have to work that hard.

Wanted to post here in case someone was searching for the same problem.

 

Pretty common story.

Hybrid battery not supplying anywhere near the current it used to from old age so all the power capability falls to the tiny little 90 horsepower motor and you have to basically floor it to get up any substantial hill. Didn't you hear the motor screaming for dear life? You never once looked at the battery meter on the mfd if you did you would have seen the battery was in purple.

So that low power low volt HIGH LOAD really stresses out the trans and the inverter and is the best possible way to destroy the transmission. That super current draw across the motor windings is a guaranteed winding blow out..

This is a very under powered car all the torque comes from the hybrid battery.

Seen many clueless posters on this site over the years with the car stuck on the side of a mountain in severe overheat. Same story. Old worn out hybrid battery car full of people or load and then they expect to be able to run up the hill effortlessly. Engine screaming all the way.
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What your smelling is the trans fluid and Inverter cooolant boiling. if you opened the hood you would have seen that. The only thing that saved you was its winter.

if I was you I would change all the fluids and oil. Pull the trans fluid I bet it smells burnt.

 

Thanks for the reply! My apologies, I should have been more specific as this is an old thread I found by googling and did not notice it was a Gen2 forum. I was driving Prius PHV (a.k.a. Prime). So the battery meter was not showing purple. In fact, the battery was nearly full at that point. Also - it definitely wasn't an "old" battery. The car is less than 18 months old.

I had the car at dealership after the event (it just happened it hit the regular service interval). The hybrid system was checked and found in perfect condition.