Prius Turns Back On After Shutdown

What @davecook89t said.

 

You may well need to disconnect the 12 volt battery (including both sides of the ground wire) and clean off corrosion before reattaching. Check both battery terminals, and where the ground wire connects to the vehicle body. Also check for corrosion on the actual washers and clamps which make the connections.

 

Thanks for the replies. I will check the battery connections today. It’s not acting like the 12 battery is bad. It been going below 0 degrees here pretty regularly and the car starts right up. I am just worried it is something really strange that is going to be hard to track down. The symptoms are so specific and you would think unrelated. It actually didn’t even occur to me they were related until I googled Prius clock not keeping time and found this thread. These issues are something I can just live with as long as they are not leading to something worse.

 

any update on this? I'm having the same exact issue. It started several months ago at which time I charged the battery (didn't have it tested though) and after it has been fine. Now it's doing it again - exactly as described here.

 

This system is complicated with several interacting relays and modules thru BEAN, CAN and LIN and proper troubleshooting without OBD2 codes would be extremely challenging even for the dealer. In situations like this you might want to start switching parts which I am pretty sure any technician would try too.

I would replace the power switch first and probably the Power Source Control ECU next with inexpensive used parts.

 

Anyone ever get a resolution to this? I keep seeing these posts during google searches you arent the only one it just started happening to me looking for resolution.

 

have you already tested the 12v and related connections?

 

I am having the same issue . Any cheap resolutions?

 

Been a bit since I've dealt with this one, but memory says if the car is not in READY mode and gets turned off by something other than the power switch (ie, the 12v battery is disconnected or dies, etc) the Power Source ECU remembers that the car is supposed to be on. When you reconnect the battery, the car turns on. It will continue to do this until it's put through a normal shutdown sequence.

 

I'm using the power button which is weird. I don't get it. Probably going to need to a diagnostic at the dealer.

 

Yes, that's mentioned in the repair manual somewhere and I've also noticed it myself.

It's like that checkbox in your desktop computer's setup where you can have it remember its last on/off state when failed power comes back.

But it has always seemed to me like a weird way for a car to work.

 

The problem appears to be a plastic tube that came out of the battery. Since I put that back in I have had not issues. Tube circled in pic, there is a hole near it on the battery and you can see the outline on the pic. It's very close to where the tube is.

 

Coincidence. The vent tube can't turn your car back on any more than it can start your lawnmower. It's there to keep battery gasses from killing you.

 

I have the same issue happening with my 2008. I bought it at auction and immediately replaced the 12V battery. Also noticed at the time that the rear hatch leaks so that water occasionally pools in the 12V battery compartment which I have learned is a common issue. I check the compartment after rain and dry it out if needed. It doesn't happen every time. About a year passed and then another 12V battery after red triangle and warning lights. Last month I left an interior light on over night and then this issue started with the car wanting to come back to life after shutting off - and occasionally not wanting to start. I found that slamming the left rear door brought the car back to life if it was dead and wouldn't start. Therefore, I am pretty sure this is a loose ground or battery connection issue. The fact I have burned through two 12V batteries seems odd. As far as reconnecting the vent pipe - you likely bumped the battery and inadvertently made a poor connection better for a little while. I will repost after checking my grounds and connections, but am curious if the occasional water/moisture - and probably ice in the battery compartment is killing batteries. Has anyone experienced this and installed a drain hole in that compartment?

 

Maybe.

There is already a drain hole in the battery well, facing forward into the wheel well. You can remove it from the outside and reinstall it once you have fixed the leaky seams.

There are lots of posts where people have experienced water in the battery compartment (and worse). Search "Leaking Hatch" using the Advance Search option (Click on the More... button) in the search window above) and limit your search to All Gen 2 forums and child forums. The fix is reasonably straightforward.

 

Whats odd about the second battery dying? You left a light on all night which is the best way to kill a battery and best way to damage it. There's a load across it till its dead then the load holds it at zero volt for quite a while. Not good that will cook the battery. So you killed the second one.

There's a drain plug in the bottom of the 12 volt battery well. And one under the spare tire.
If the car lives outside just drill a small weep hole in those rubber plugs. if car lives outside do not remove them as mice will get in there really quick.

If troubleshooting the 12 volt battery it only matters what the voltage is at the front point. Owned my Prius 14 years never once checked it at the battery cause it does not matter. Many many battery tenders on the front jump point over the years too.
The 12 volt battery has to go through 9 connections (ones a 100 amp fuse) and a long power cable till it gets to the front jump point\fuse box.
Many joints to fail.

The most posted bad connection is where the battery negative cable is bolted to the body. The cable/body connection.

This one:

 

Had the battery checked at the auto parts store and no issues with it - so no third battery this time. Found the hot connection on the battery loose and corrosion at the body ground. Emery paper on both, some lithium grease, and reconnected. No issues since. Also located the rubber plugs and drilled 3/8" holes. Thanks for the reply.

 

There is already a drain hole in the battery well, facing forward into the wheel well. You can remove it from the outside and reinstall it once you have fixed the leaky seams.

Thanks for the tip! Battery and water issue might be fixed.