Help, My Car Came On By Itself!

sadly strange things occur when your 12v is bad. Check that and get it charged or replaced

 

It sound like a sticky electrical contactor. Electrical contactors after my cycles get worn and pitted and don't make good contact or they don't release when they are suppose to. The ones I am talking about are in the HV battery. I'm no expert on Prius but have electrical background.

Contactors at 2 minute mark.

 

@TwoPriusInTenn Is there any difference when you don't insert the fob? I can't tell you the last time I put mine into the slot. Come to think of it, I don't know what purpose the slot serves. Does it resync the key or something?

 

only on non sks model, or if the switch is turned off or something is wrong. (low battery, fob programming)

i'm amazed you made it to 300k!

 

I’m at 490k and I’ve never had it start on its own though with the display out I’ve had it not turn off and fool me. I had to start being really sure it was off, pressing the power button for three seconds and then sometime that only stopped the engine so I had to press the power button three times quickly to turn it all off.
One thing I know is that it will not lock if it is not off! So that is my triple check.


iPhone ?

 

If this is a non-SKS basic Prius, the slot should not let the key go if the ignition is still on, unless it is forced, worn out, or he has the bad combo meter problem and when it is dark, it releases the key!

Did you check with ignition on? Even a new battery can be/go bad. What is the voltage of the battery when the inverter is not trying to charge it? (after sitting overnight without getting a charge from the inverter.)

 

Have you had to jump start the new 4 month old battery?

I doubt the car is coming on by it’s own I bet what’s happening is the car has been on the whole time you just never realized it because the combo meter is dead.
Before you walk away from what you think is the car off floor the gas pedal which Makes the ice come on. That way u can confirm the car us actually off.

We don’t really care what the charging voltage is on the 12 volt battery we care what the sitting and load voltage is.

Get a dvm. With CAR OFF Measure battery voltage at front jump points. Write that down.
Then with CAR OFF turn on the headlights in high beam for 5 minutes and measure battery again.
Report back here.

My car with 2 year old yellow top measures 12.6 volts sitting and does not drop one volt in the 5 minute headlight high beam test.

 

congrats, well done!

 

And many thanks for reporting the solution, it may help the next person!

 

And that’s why all charging and all 12 volt battery diagnostics should be done from the front jump points.

A simple headlight load test would have found that in about 15 seconds.

 

Another case of the 12 V. battery causing weird things in a Prius. Glad you figured it out.

 

So, 12v batteries that are dying or have loose positive terminals cause weird symptoms, got it.

BTW, it was the 12v after all, I was suspecting the female key hanger.