Power at 12v but not at front terminals.

Well, that wire disconnects from that battery fuseable link somehow. Sounds like you need to run a new wire.

 

I have the same exact problem! Not sure what is it! Did you figure it out?

 

In the first Post you said you dont get anything across the 2 "terminals" under the hood..

There is no terminals. Just the one post under the red flip up cover in the black fuse box. Thats the positive lead from the battery. Its bolted right to that post/bolt. There;s a little right angle piece of metal bolted on the post toyota put there so you can clamp a jumper or charger jaw to that tang. That little metal plate is 12 volts positive right from the battery.

Measure from that metal tab to ground with your dc voltmeter. We usually use the bare nut right above it on the strut tower as the ground point..

 

That’s exactly what I measure that show me 1.7 V
Thank you

 

Here we go....I'm going to put some effort into this tutorial. This really very basic troubleshooting for anyone familiar with electricity.









To remove the 120 amp fuse, you'll need to remove the assembly from the battery. Unplug both cables and open the covers. You'll need an 8mm socket for the top screw and a 10mm for the bottom.

 

I really appreacite all the work! Yes I have checked all of those connections which leads me to think that there may be a short somewhere on the cable. I just don’t know where to start and end (not sure how it connects or what may be happening. I checked the metals connections that attach to the connectors and it does have 12V and is tightly placed. Whenever I jump start it, it clicks several times like 10 times like a relay and then it powers on. And then the designated jumpstarting connections have 14V and the rear battery has 12V

 

Have you tried having your leads on the (-) post and on the metal in the plug and have someone press the power button to see what voltage does? You disassembled the fuse assembly mounted on the (+) battery post to make sure the screws are tight? A loose connection can easily pass full voltage when not under load.

I've even experienced a 12v battery that was <6 months old that read perfect voltage, but dropped to 0 as soon as a door was opened and the interior lights turned on. Internal bus bar failure.

 

Yes I actually did because I thought the problem was there but everything looked good and well about the battery...it was load tested by autoparts store. It was their battery still under warranty. You think they lied to
Me? The battery is currently reading 11.8V and stable at 11.8-11.9 V

 

Like it’s been holding the past few days at 11.8V. It’s from carquest and I went to their store asking about it and they said they would charge it and tested for me and I can back the next day and told me they will test it again and said it was good. I am not sure. Would they be losing if they exchange my battery?

 

Also the car is completely powerless so I cannot test that. Nothing is on until jumpstarted. It clicks serveral times and turns on

 

Henry,

As soon as a jumper cable is connected to the jump point, it energizes the fuse box. When you hit the power button, the car starts up as it normally would and the inverter takes over to supply the 12v system. At this point, the inverter (DC DC converter) is powering the 12v system, typically at around 14 volts. Once you shut the car off, the inverter shuts off and the 12v system should again be powered from the 12v battery. If the battery/cable is unable to provide 12v to the jump point, the car has no way of powering up again. If you're confident you have power at the big white plug, but no power at the jump point, then you have an open circuit somewhere between the big white plug and the jump point. Perhaps the main cable has been damaged somewhere or is no longer making good connection at the fuse box jump point.

When the car is running, does the voltage at the battery posts also increase to 14 volts or does it stay at 12v?

 

You may have a damaged main power cable from battery to front jump point. Hard to damage it as it’s a big conductor and runs under protective cover under the car. Tear up anything under the car lately? You really have to incur big damage to get to that wire.
Seen one or 2 of those in the last 12 years on this site. And they were very obvious.

Let’s test that main power cable.

Get a long piece of speaker wire or lamp cord about 20 feet long.

In the trunk disconnect the big black wire that’s plugged into the positive battery black plastic assy. Not the thin black wire the big one,
Make each end of your speaker wire bare so you can measure it with an ohmmeter and stick one bare end into that black lead white plastic terminator clip as best you can. You may have to cut down the copper conductor a little to fit into the plug.
Make sure it’s touching good. Tape it up or have someone hold it.

In ohmmeter mode on your voltmeter measure the other end of that wire to the main front jump bolt.
You are then measuring continuity of that main power wire. Meter should show like 1 or 2 ohms.
It should show close to a dead short meaning the wire is intact and fine. If meter is blinking OOO the cable is open and damaged. Touch the ohmmeter leads together to test the meter should go from blinking to like 1.

If you don’t know what I’m talking about that’s the main problem.

 

That's really low, the kind of voltage you would see after leaving a door open overnight

 

Yes it is. The little chart that came with my Toyota battery says 11.8 is 20% charged. Basically a dead battery.
Kind of a moot point though since the Battery isn’t charging when the car is running.

 

Okay people I think I found my issue. May be a bad ground cable or connection. I checked multiple times and every time it was good at near 12V. Today I was going to get a replacement and about to disconnect the battery and remove it to take to the auto parts store and the car powered on. I have bad connections on eithe the ground or the positive. Now there is 11.9V at the front terminals and the back terminals. I don’t know how it happened so don’t ask me. I tested them multiple times and I always read the same voltage as the battery. Well now I have power at the front terminal and I did no touch the connectors at all therefore leading me to think to a bad ground cable

 

Hope this is noticed - not optimistic since the thread is old
I have the same problem too, Google lead me to this forum - essentially I have no voltage at the front jump terminal but 12V battery is good.
If I just run a single red jumper cable from the battery rear +ve only to the jump terminal in the engine bay everything is normal ( so assuming ground etc is good since only a +ve is needed )
@BobThePrius if you have any hints on how to fix/replace the wire that will be great .

 

There's a fusible link inside the 12v battery + connector housing. Is there a chance you've had the fusible link go open?

 

You may find the tests in post #26 of this thread will reveal something useful.