Pesky problem with transmission "P" lock, red triangle, or parking pawl.

The service manual has a test for the actuator and Luscious Garage has a video, showing a way to make sure if its having a problem. Its all electronic/magnetic with now contact parts in the actuator itself. It looks like there is an orbital gear ring that is greased. If it turns easily, its likely ok. Mine was acting up and turned out to be a P-CON connection issue due to corrosion in the harness or the HV battery was tripping the code. . I traced it out using the suggested protocol in the service docs. I noticed that the P-LOCK error didn't clear when I disconnected the aux battery, but certainly did when I disconnect the harness from the trans EMU and the HV EMU. In any case I think mine is fixed.

 

Here's to hoping it is just the connection.
Replacing the prawl can be a challenge.

 

You can get access to service manuals via Toyota for a daily charge. Or buy hard copy on eBay.

 

Engine Management Unit.

 

its either low battery voltage or its bad wiring to the left side of the p con fuse under the hood, you need to jump the blue wire number 4 from the left to the left side of the p con fuse, simple, you tube it, you will see
if you drive in salt then that car is going to have tons of under the hood fuse issues and will even take down the main power to the power train control module in pass glove box and prevent trans from working at all, been there, done that, salt roads and a prius under hood fuse box

 

or another possibility as covered in the workup procedure in the repair manual. John McG.'s procedure in #21 is best, just do the diagnosis and find out what's causing the trouble in your car. Following "it's always X" posts on PriusChat or youtube can work sometimes, but can also lead to mistakes you'd avoid by diagnosing the car that's in front of you.

 

Bumping this old thread in case anyone finds themselves here with the same problem. Mysterious "Park Lock" Red Triangle & my 2005 update | Toyota Prius Forums