2008 Prius won't start, is it a Short? Dead 12v? Fuse? Something Worse?

Did you measure the 12v battery? Odds are its bad. So bad that a jumpstart has a hard time bringing the voltage up enough to run.

 

THIS.
Odds are GREAT.

Second most likely cause: Loose or corroded main battery cable connections.

Or a combination of both.

 

Try charging and cleaning 12v first.

Posted via the PriusChat mobile app.

 

I suggest from experience you disconnect the 12V bat. You can do that by either removing the negative terminal from the negative battery post, or by unplugging the large white plug from the positive terminal connection (I'm not 100% sure your 2008 model has this large white plug, so if you don't see it, just remove the negative terminal instead). Disconnecting the battery will clear some codes and reset various things - like programmed radio stations - but these may have already been lost by your 12v bat getting low.

Now charge the 12v bat with any normal battery charger. It may be best to leave it charging overnight. Most battery chargers will start at 10 or 5 amps and revert to "trickle" charging at 2 amps once the battery gets close to being fully charged. Some battery chargers will indicate that this has occurred and give you a green light that the bat is good, or an indication that the bat is bad.

Disconnect the charger.

Reconnect the negative terminal (or reinstall the big white plug).

Get in the car and do what you normally do to start it. It probably won't start and many warning lights will come on, fuel will show zero, etc. Wait about 30-45 seconds. With your foot still on the brake, push and release the power button again. The car will likely start.

You probably have a bad 12v bat.

Of course instead of all the above you could just install a new 12v bat right away.

If you want to keep using the car prior to replacing the 12v bat, and you have a secure garage to park in, you can repeat the above process. Leave the "trunk" open with an old 2x4 to allow you easy access once the bat is disconnected. It's a little more complicated if you don't have a secure place to park, and you'll need to use the metal key to open the door, and crawl into the back to get to the bat/open the "trunk".

Good luck. ;-) These cars are a helluva learning experience!!

 

So I have an 08 Prius and every time I go to leave the car is dead untill I slam the door then lights come one and it even started up by itself freaked me out but every time I get in I have to slam something to get it to work

 

maybe a loose connection at the battery or neg to ground, or even inside the battery.

or something loose in the fuse box

 

I second that.

Go check (or have someone check) for loose connections back at the battery. There are three connections that are important they are clean and tight. Also, check the white connector (attached to the fat cable) attached to the black block on the positive terminal of the 12 V battery.