Good day Scotty. My parents have a 2015 Prius and for some reason at low speeds, the steering wheel feels heavy to turn and it has been doing this for over a year. Problem is that now it feels heavy compared to when it was new 7.5 years ago. It was much easier to steer back then than it is now. What is wrong here?
I'd pray it's just a weak 12V battery, otherwise the it can get very complex and expensive.
Sadly Toyotas of this era had very weak EPS ECUs, but you should diagnose it before replacement.
When I had an EPS failure (not on a Toyota) it turned out to be $2 plastic couplers, but it does require a skilled mechanic that knows what he's doing and what to look for.
Service manual for a Toyota EPS: https://hybrids.ru/wp-content/uploads/2021/04/PS-Power-Steering.pdf
(might not be identical to what you have, but should give you an idea as to what the diagnostic process should look like)
