Rat and wiring

There are as many as a dozen different ECUs in your Prius. Which ECU does the dealer say needs replaced?

 

Couple dozen, in gen 3. I assume the dealer means one of the ones involved in the smart key system, but yeah, it would be good if they said something more specific.

 

One of my Italian motorcycles has an antenna wire that literally is wrapped around where the key which is a transponder key that slot has a fine wire wrapped around it that is literally the antenna that detects the transponder key if that wire gets damaged or anything like that than the red light will never go off on the dash of this bike and it will never start I have taken it apart and seen this antenna I also rerouted it and all of that and for the last 15 years it's had no problems and never does I have seen people spend two and $3,000 replacing the digital LED display on this Aprilia maxi scooter before with no resolve so things like this do happen You could go to a generation 3 which there are plenty of in salvage yards as of now and get all the computers you want places like LKQ could care less about that silver gray colored box with a plug on it or receptacle in it they will be happy to give it to you for $20 I can almost guarantee you I get them all the time and usually I'm not doing anything with them throwing them in a box.

 

I'd watch this video first.

Basically, use either Techstream or a high level OBD scanner to diagnose the Smart Key module.

 

A lot of these dealers won't even check for bad wires until you get a new ECU, then it still won't work and they'll say you needed it anyways, even though you didn't. You pretty much never want to deal with a dealership (if you are out of warranty) for any reason other than parts.

Past rodent issues and more evidence of rodents would make a pretty strong case for wire damage. I realize it's easier said than done, but I'd check for wire integrity before I got any new ECU. Or, find a true diagnostician to look at the car.