Prius only Starting after Jump

I suggest that you use a large flat screwdriver to pry off the red plastic cover so that you can easily see what is going on. There will be one very fat cable that is connected to a 120A fuse. Use your meter to verify that there is 12V on both sides of the fuse, and that the cable also has 12V. You should be able to find a problem somewhere there.

If not, pls take a sharp photo of the positive battery terminal after removing the red cover, and post.

You will also see a very thin wire that is connected via a 5A fuse, and that provides sense voltage to the DC/DC converter so that unit knows how much voltage is being provided to the battery when the Prius is READY. There should also be 12V on both sides of that fuse.

 

It might be better to use a needle to pierce the rubber so that if the fuse is OK, you don't loose that protection.

 

I am in same situation. When I check the battery voltage it shows 11.5 V but it wont start the car. I have to jump it always to start it.
@Baquio: What worked for you?

 

Two possibilities: 1) your 12V battery has a low charge and needs to be recharged or replaced. 2) A battery cable is loose which introduces resistance into the cabling and reduces voltage further, as you try to start the car.

 

Yeah a battery in so-so shape would be showing voltage of AT LEAST 12.4 volts; 12.6 or higher is good shape. Voltage readings can vary, and don't really check the battery's capacity: get it checked out with an Electronic Load Tester. Automotive retailers often have them and will usually test for free. Dealerships will have the tester too, but charge maybe $75~ to test.

If you want to DIY the test google Solar BA9, for one such tester. They measure Cold Cranking Amps, and typically give a verdict on the battery, whether or not it's viable, needs charging, or a dud.

 

Any updates guys? Same problem.

brand new battery

all battery wires checked.

but car just start when you connect the jump or another battery.

 

Check voltage at jump point? That’ll check if there’s a loose connection somewhere.

 

That information might have been useful for him........about 9 months ago !!

 

Some posts just need a little time to ripen. #30 will come into full flower just about 9 months after post #28, so around the last week of January 2022.

 

I’m asea.