2010 Yellow Triangle with exclamation point - Starter switch?

Any lights on the dash?

What exactly did happen, if anything, when you stepped on the brake and pushed the switch?

 

Starter switch? Do they mean the start-stop button. $700? Not likely. Used ones sell for almost nothing on eBay.

I don't believe that's likely the problem. It switches 5 volt ECU very low amperage currents. It might be the relay, but that's not likely, either.

I'd check the 12 volt battery first.

 

+1.
^ That.
Autozone has an aftermarket replacement for $50.
Look for a Duralast Ignition Switch LS1531 which you can get and install in the same day.
There are about a half-ton of used OEM switches out in the wild for about $40 if you don't mind waiting for the mail.

Yeah.
The Duralast is an el-cheapo replacement, but if it fixes the car it will last until you can get a new or used OEM switch.....and if it doesn't fix the car then AutoZone or wherever you buy the part might allow returns......and let's face it.
It's a glorified doorbell switch for goodness sakes.

The dealer is gambling with YOUR money and they're making some pretty stupid bets....but, hey.
It's YOUR money.
FWIW, the MSRP for the switch is about $250 in flyover country so they're either wildly over-charging you for the part (which probably will not be the problem) OR they expect you to believe that it costs about $500 in labor to install the part.

Either way?
I'd tell them that the Earth will be orbiting a cold, dead, star before I gave them another dollar.

I noticed that you're not listing your location, which is actually pretty smart, but it's it's some place where there are a lot of Priuses, then I'd shop around for an independent mechanic. If your 2010 G3 is your only means of transportation, and your life situation does not happily tolerate unreliable transportation then I'm guessing that you're also a little price sensitive about repair costs.
If they charge you $750 for THIS what happens the next time that the "change owner" light comes on?
Or the time after THAT?

Normally?
An almost 12-year-old Toyota with less than 100,000 miles is a pretty safe car to own.
HOWEVER (comma!) you really need to think about this car as a star athlete that's on the back half of it's career, so you're really going to want to either BE or HIRE better mechanics.

Mice.
They LOVE chewing on Prius wires.
ANY electrical problem is a good opportunity to look at your cabin air filter.
It' costs you nothing to look there, you can bang out some of the dirt or even replace the filter, and rule out nesting mieces.

Good Luck!

 

Not really. A few years back, I disassembled one. All Gen 3 switches are the same, with the ones starting in 2012 having blue colored centers, instead of black. These have internal circuit boards with multiple pin connectors. I have maybe five used blue ones laying around; some with connectors and pigtails cut off of the wiring harness.

 

The Duralast one from Autozone is most likely made by the OE manufacturer, No after-marketer would spend the amount of research and manufacturer to make a duplicate for that price.

 

The yellow triangle with the exclamation point means that there are diagnostic codes waiting to be read that will explain why the power management control ECU has made the decision not to start the car.

At this point, I'm not seeing any reason to be talking about the power button, whether OEM or aftermarket. The car knew you pressed the button; that was why the lights came on and then the master warning light.

The main thing I see a reason to do at this point is to post the diagnostic codes so we have more information on why the car is electing not to start.

 

The relay, Toyota Part # 90080-87024 is universally used in many Toyota models.
https://parts.mcgeorgetoyota.com/oem-parts/toyota-relay-assembly-9008087024?c=bT0xJmw9NCZuPVJlY29tbWVuZGVkIFByb2R1Y3RzJms9MQ%3D%3D

Check its location in the link to the fuse box diagram;
https://fusecheck.com/toyota/toyota-prius-xw30-2009-2015-fuse-diagram

I have a few of these and other Toyota relays, too.

 

GET THE BATTERY AND IT'S MAIN CONNECTIONS TESTED.

ANY time a shop wants to start replacing parts on a guess, you need to get a written agreement that if the guess flails, the cost will be on THEM and not YOU.

 

In their own Repair Manual, in the workup section for B2784, replacing the power switch is the next-to-last thing to try, after checking the wiring between the certification ECU and the power switch (ECU pin 12 to switch pin 9, and ECU pin 13 to switch pin 10).

That aligns with my own intuition that, of all the places for a short or open to develop somehow in that circuit, the antenna and transceiver built into the power button might be less likely than something more exposed. (The only thing they put after trying a different power switch would be swapping the certification ECU itself.)

I am not sure that the B2784 issue would block you from starting the car, unless your fob battery was dead and you needed to use the hold-fob-to-power-button method. For that, it would definitely be a problem.

The U0110, however, is a failure to communicate between the power management control ECU and the MG ECU inside the inverter. The U0115, I think, is a failure to communicate with the engine's ECU. I could see either one of those codes putting a serious crimp in the ability to use the car.

The old download of the repair manual that I am looking in does not have much troubleshooting information on those two codes. (There are references to sections not included in the download, which might simply have been missed.) There is probably more complete and better information in the up-to-date Repair Manual online (more info).

 

sounds like corrosion, are you in a humid environment?

 

The start-stop button almost never goes bad. There is almost no market for Gen 3 buttons, and there is a surplus in Toyota's possession. They do not fit Gen 4's. That's why Autozone can retail them for $50,

 

it can build up over time. the ecu connections corrode and cause voltage issues leading to trouble codes