2012 Prius goes into neutral, won't stay in drive/reverse

'04 to '09 is generation 2 I think you have a generation 3 and you're on the generation 3 list portion of the site I do believe so unless you're in a foreign country and an '09 is actually a 2010 which can be? If your shift lever is blue you're driving a generation 3.

 

As described, an electrical intermittent, likely the shift switch. Can you clean it with an aerosol contact cleaner?

Suggestion: don’t drape anything on any of the stalks.

 

I believe that this was the problem. I read some time ago of a similar problem that someone had with their gen 2.

 

It sounds like the nuetral safety switch is going out. I believe Toyota calls it something else.
I can't remember the name. Hopefully someone who knows the correct name will
type in.
It's an electronic part and something inside starts to break not allowing the contacts to move.

 

Neutral safety switch isn't a thing, and there aren't any contacts involved in the shifter control. The lever just moves some magnets around, and there are electronic Hall effect sensors (no moving parts) sensing the magnet positions.

The car will shift into neutral for various reasons. The usual reason is when you move the shifter there (or the electronic signals say you did); the car then shifts to neutral after a short delay. There is no warning light or sound with that, of course, because it thinks it just did what you told it to.

It will also shift to neutral instead of making some other shift, say if the car is moving too fast. Say you're driving above 7 MPH and you move the lever to R (or the electronic signals say you did); then the car will go to neutral instead. For that, you hear a little beebeep, but there is no warning light; the car doesn't think there's anything wrong, except the silly driver said to do something dumb, and the car said nope (the beebeep).

The electronics in the shift lever measure two things: the up/middle/down position (called "shift") and the left/right position (called "select"). So neutral is (shift middle, select left) and D is (shift down, select left), and B is (shift down, select right).

Both those sensors are duplicated for redundancy: there are two independent "shift" sensors (VSX1 and VSX2), and two independent "select" sensors (VSX3 and VSX4). Naturally, VSX1 and VSX2 should always read the same, and VSX3 and VSX4 should always read the same. If the car ever sees VSX1 different from VSX2, or VSX3 different from VSX4, you will get warning lights and trouble codes. Those would tell you there's an actual malfunction in the shifter or wiring.

So, if there are no warning lights, you don't have an obvious malfunction, the car just thinks the shifter really moved. If it went to neutral with no beebeep, it thinks the shifter really moved to N. If it went to neutral and beebeeped, it thinks the shifter told it to do something inappropriate and it went to neutral instead.

If it thinks the shifter moved, you should first make sure that isn't really what happened (the headphones hanging on it, for example). It's less likely for that to be a problem in the electronics, because for that to happen and the car not notice it with warning lights and codes, it would be necessary for more than one independent sensor circuit to flake out in the same way at the same time.

You can see the details and troubleshooting ideas in this attachment:

https://priuschat.com/attachments/hybrid-control-system-lever-pdf.43306/

If troubleshooting is needed, Techstream, or another scan tool that can show live data, can show you what the VSX1 and VSX2 ("shift sensor main" and "shift sensor sub") and VSX3/VSX4 ("select sensor main" and "select sensor sub") inputs really are doing while you move the lever around.

 

Actually I think behind the dress or plastic the shifters are actually very similar not really much to them at the point where you're putting your hand and what's right behind your hand it's a very simple looking electronic switch it seems like not what the computer does with those input informations and all this VX1 and two businesses well there you go but that's further down the line from your hand I think I've had the shifter apart and the generation too quite a few times because I've had the dash out on a few cars on the generation 3 I've had the shifter knob off the car and I've been behind and looked at most of the shifter assembly which looks very similar nothing like your normal automatic shifter for sure obviously nothing like a manual but it's just seemingly simple switches in a plastic housing with a shaft sticking out of it for the tulip or the knob to go on whichever you have I would think it would be pretty tricky for that part to really go bad the unit I was working on somebody had spilled coffee down the dash the generation 2 and that it caused this switch to stick if I moved it over to any of the positions that would not flip back to neutral it would just stick there like glue upon closer inspection I was easily able to see and smell the coffee in the sugar cleaned all that up still driving the car today.

 

... or press the Park button...