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Boxer54, Toyota Technician
Category: Toyota
Satisfied Customers: 1755
Experience:  ASE Master tech with L1 certification, Toyota Master Diagnostic Technician
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Toyota Prius Prius wont start, I changed the 12 V battery

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Prius won't start, I changed the 12 V battery and it still won't start. It started yesterday when we jumped the 12 V battery, this morning we tried it, all the warning lights came on, flashed a lot, then went off, we put in the new battery but it wont start.
Thank you for trusting Just Answer with your Toyota question. What led up to this? Was the dead 12v battery the first indication of a problem? Have you checked the fuses at the possible terminal of the 12 volt battery?
Customer: replied 6 years ago.

Dear Mr. Boxer Dog. You look kind of like my dog.


I suspect that the car was left on - as people sometimes do with Prius cars since you can't hear it run. In any case, on Sunday I went out to start it and it was dead. We jump started the battery - directly to the battery in the back, not the little jump-start thing on the fuse box in the front. It started up ok but I did'n't drive it anywhere. I just turned it off a few minutes after we started it up.


So this morning when I went out to go to work I realized that it was not right. I could unlock the door with the remote, but the signal was weak. then the car started also with the remote, but only the dashboard lights flashed and flashed - all of them, it was kind of scary!. So I turned it off, and it hasn't started since. We tried to jump it again, didn't work. I went to Toyota and bought a new 12 v battery, didn't work. My husband looked at the fuse, it seemed to be intact, but tonight we couldn't replace it. He thought it looked ok though.


It's a 2005 Prius with 150K miles on it, I had never replaced the 12 v battery yet, so it made sense to me that it would die. But now, even with the new one, we don't get any dashboard lights, dome light, beeping when the door is open, anything. No response at all.


HOpe you can help!

Sorry for the delay, have you tried to jump start the vehicle after replacing the battery?
Customer: replied 6 years ago.
Yes, with the new battery in we tried to jump start but no response. No lights, no noise no anything,.
Do you have access to a digital voltmeter?
Customer: replied 6 years ago.
No sorry don't know what that is...I took the new battery to Kragen Auto Parts to be tested, they said it is charged.
What we need to do is check at the jump start attachment under the hood for power. To do this will require a voltmeter or a 12 volt test light. The test light can tell you if there is any power at all, but I recommend the voltmeter as it will tell you how much power there is. I recommend you get one of them to help us figure this out. Either of those 2 pieces of test equipment can be purchased at your local auto parts store very cheap. We will need this information.
Customer: replied 6 years ago.
WE just may have one! My husband is looking. Otherwise it will be tomorrow because right now its after 10:00 here where we are. Do you stay up all night trying to help people fix their cars?
Its actually just after midnight central time for me. Let me know if you can locate a voltmeter and whether there is battery voltage at the jump start attachment under the hood. I will be logging off for the night, but will be checking on this q&a session first thing in the am before I head to my real job.
Customer: replied 6 years ago.
Thank you, XXXXX XXXXX find the voltmeter, but will need the cables it attaches to. My husband will check tomorrow afternoon to see if there is battery voltage under the hood.
Thats perfectly fine. Keep me posted and I Will be happy to respond as soon as possible after you post a reply.
Customer: replied 6 years ago.

Hi there we are back. We tested the jump start attachment under the hood. with the voltmeter. There is no voltage to it - it shows "0"


By the way, we also tested the old battery and it is still 10.59. I wonder if it could be slow-charged instead of replacing it - it's already 6 years old and 150,000 miles.

The most likely cause of this is one of the fuses at the battery positive terminal is blown. There is a small 5 amp fuse and a much larger rectangular fuse(which is likely our problem.) It is a 120 amp fuse.
Boxer54 and 3 other Toyota Specialists are ready to help you
Customer: replied 6 years ago.

Is it a fues that is by the battery itself (in the baci?) or in the fuse box in the front?

Its the one directly on the positive battery terminal post in the back.
Customer: replied 6 years ago.
I think we found it but we dont' know how to get it out. It seems to be stuck in there - any ideas?
Some of those are bolted in place. Give me just a minute to do some digging.
Customer: replied 6 years ago.
Any luck? We have kept trying to get it out but it won't come out. We can see it, it is clearly blown out. It's a rectanglular box with a clear plastic top that says :120 amp. So if this isnt "the" problem it's certainly "a" problem. Just can't get the dang thing out.
Sorry. I went offline last night meant to tell you I needed to look a little deeper this morning. Doesnt show for sure in the materials I have, but I will check some other things this morning and let you know what I find.
Customer: replied 6 years ago.

Hi there, after we detached the positive battery terminal - it just unscrews - I took it to our Toyota dealer today. The fuse is bolted to the part - to unbolt it, the sides of the part lift up on plastic hinges to give access to the bolts that screw the fuse in. After I saw the guy at Toyota do it, it was all very simple. Toyota didn't have the fuse, I just picked one up for $5 at Kragen auto parts. Now the car works perfectly.


Thanks for your help, none of the reference books or the on-line chat rooms had any information at all about replacing this fuse. It was something we never would have figured out on our own, We were ready to tow the car to the Toyota dealer, all for a simple fuse!


Sorry, wasnt able to get back online until late this evening. Glad you got it going.