Gen 2 shifts on it's own from drive into neutral!

I would think a new/different shifter would be best option. You can find them really cheap, they don’t normally fail so there is an abundance of supply

 

I think you should try to find a dealer who has heard of cars that are controlled by computers, and thinks about asking the computer what it shifted to neutral for.

 

Have you been drinking?

 

Little bit of coffee, most recently.

The Prius "shifter" is a lever that moves two small magnets around next to some Hall effect magnet-sensor ICs.



The ICs create a pair of voltage signals that are inputs to the HV ECU, and tell it what "gear" you would like to be in. Roughly speaking, it's a game-controller input.

As gets pointed out daily on PriusChat, there is nothing inside the transmission that physically shifts (aside from the piece that stops it from moving in Park).

All of its other behavior, including neutral, is generated by the HV ECU, according to what "gear" it decides it is in, following your input from the game controller.

There are a number of conditions that will make the ECU change its mind about what "gear" it is in.

Any dealer who looks at a Prius that "shifts into neutral" and whose very first step is anything besides "ask the HV ECU why it did that" might be happier in another line of work.

 

Easiest way to address this is to go to a junk yard and pull a shifter out and swap it with the one in your car... Only experience I've had we these shifters going bad is the return springs not working, which could be dangerous in some situations.

 

I wonder whether such an issue would be more about the return spring or about the grease in there getting peanut-buttery with age (which would make the return-spring action sluggish even if the spring is ok).

I don't think the spring gets flexed anywhere near its elastic limit ever in the few cm the shift lever moves, and I'd be surprised if anyone has ever shifted a Prius enough times for the spring to fatigue.

I'm pretty sure if mine ever were returning sluggishly (and if I confirmed that the reason the ECU was shifting to neutral was because it really got that signal from the shifter), I would just take it apart and clean out the old grease and regrease it and see what that did. I've had it apart and there's nothing difficult about the disassembly/assembly; it's a simple mechanism.

My nearest U-pull yards are a half-hour drive or so, and I could probably clean and regrease a few shifters in the time to go pull one.

 

The Prius I was referring to was an '04 Gen2 with date of manufacture of November 2003 and it was driven in areas with salty roads and was trashed in most every way. There was zero resistance from the springs, just kind flapped around in the bottom slots due to gravity...

 

I can see where the ECU would shift from an active gear to neutral on a problem, but not without throwing a code. If there is no code then perhaps the ECU read "something" as a command to make that change, suggesting a problem at the shifter or in the wiring in between.

By any chance are there any knick-knacks, phone holders, or other nonstandard car items near the shifter? I suppose it is possible that a cross or some other chunk of metal might be magnetized enough to confuse the shifter mechanism. (As precedent, I have seen video clips where people could not start their cars, and the problem was a little metallic bling ring they had installed around the key barrel on the dash or steering column, which blocked communication to the active part of the key.)

Another possibility is that the connection from the shifter to the wiring harness is corroded or dirty. Might be worth a try unplugging it, giving both sides a blast with some electrical contact cleaner, let it dry. Examine it closely for problems, and if none are seen, then reassemble.

 

exactly—and that's also something you'd confirm by checking what is and isn't recorded in the ECU.

You can also data log the signal voltages coming in from the shifter, so you know what inputs the ECU is getting.

Keep in mind that the ECU does not act immediately on the input voltages that signal "neutral". It has to see those voltages held for about a second. That's long enough to catch on a data log, even at a low polling rate.

 

Sticky spring?

 

I assume you’ve checked the transmission fluid level?

 

The fluid in a Prius transmission has a lot less opportunity to escape than in a conventional automatic. It's more like a manual in that way: there's no dipstick, there's a fill and a drain plug, and when you drain it, you generally find the same amount of fluid you filled it with.

 

Why, exactly? I suppose if there was a major leak the car would eventually detect that the transmission is too hot or the gears are binding and might go into neutral, but not without throwing a code. Remember, while there are gears in the "transmission" no shifting of said gears occurs. Also, there is no dip stick, the only way to check is to drain it and see how much comes out.

 

Haven't seen this type of fault myself, but if it is intermittent, then no springs in the shifter are "broken" (as it would be a problem all of the time).

Old grease and dirt in the mechanism can certainly be worse when the temperature drops.

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I would expect that if there was severe fluid loss, then the first outward sign would be bearing or planetary gear noise/failure. You might notice fluid stains on the ground- or not.

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Probably not relevant, but the one time I had this problem it was at night and I didn't see that my black backpack strap got caught around the shifter when I was getting in the car.