Won't Turn Off -- Master Warning Light on (Red Triangle)

The 12V battery would certainly be the first suspect, especially in this cold weather. If you can, connect the voltmeter to either the battery in the rear cargo area or the jump terminal in the engine fuse box. With the car in ACC mode, foot off of brake and one press of Power button, take a volt reading. Then turn on headlights and take another reading. If less than 12.0 V then you need a new battery.

 

Hi Cyberprius. The voltmeters are easy to use, just use your cheap digital one and make sure you have set on the correct range. You want to make sure that the leads are plugged into the "common" and the "volts/ohms" jacks. You DONT want to use any amp or mA ranges or jacks.

Set the digital meter to the 20V DC range and measure the voltage from the jump start terminal to any good shiny bolt on the chassis.

Hopefully it's just the 12 volt battery.

 

Yes, an overnight charge will help tell you if it is the battery or not. If after charging the car starts with no problem then you know it is the battery getting weak.

You will probably have to clear the Master Warning Light before it will start. Disconnecting the negative side of the battery will do this. You will have to restore radio presets and maybe reset the window Auto-up feature.

 

i think he was serious, not shutting hatch all the way leaves interior light on and drains battery. if it is bad, or you want to replace it prophylactically, it's a fairly easy replacement, and you can save even more with an optima.

 

Yes, you could try that.

What is the purchase price for the 12V battery from the Toyota dealer parts department counter?

 

right.

 

You can try this:

Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

We need the second number the load number.

Also if my car was seeing the 20's I would be running 0-20 weight Mobil 1. The 0 part will make it much easier for the engine to spin when it is frozen. And the synthetic would really help instead of maybe if your now running dino.

 

right again!

 

Yep, you can use either the copper tab or the silver bolt that holds it. You'll get the same reading either way.

That's pretty low for a voltmeter reading straight after a drive. As the battery is charging (typically about 14.0 volts) during the drive, then you'll normally get way overly optimist voltage readings if you measure it straight away after shutdown. Basically the longer you wait the closer it (asymptotically) approaches it's true resting voltage.

The resting voltage for a good battery would be about 12.5 volts if measured at the jump terminals with the prius in the off state. I suspect yours will be well below this when you measure it again after it's been sitting over night.

The voltage measurements taken using the alternative non voltmeter method (the MFD inspection mode method) will generally give lower readings. This is because the battery is inherently under some amount of load when performing that test. It's a small amount of load if you're in "accessory" mode, and a moderate amount of load if you're in "ig-on" mode. That's actually what makes that such a good method, putting the battery under a bit of a load gives a result which is much more telling of the battery's true health. Expect about 12.2 to 12.3 from an "ok" battery in "acc" mode and about 12.0 to 12.1 in "ig on" mode.

 

Hi-
12.34 sounds groovy but that was right after doggie trip and may have had a good surface charge on it. A false charge if you will that will quickly decay overnight because the battery is bad and cannot hold a charge for an overnight.
A common malady. The second test the load test will remove all surface charge and show you the true voltage of the battery when its need most under load.

Check it in the morning. I sincerely hope its good because it sounds awful cold up there. Too cold to take the fingers out of mittens to do any work.

And yes that bolt in question holds the little vertical metal tab. That tab is where you clamp the jumper cable too. You were right on!

So many posts of people complaining the clamp won't fit on the bolt itself. But then again side of the road in the night.....

 

I agree that the voltage reading is very low considering the car had just been driven. If you have a battery charger, you can try charging the battery for an overnight period.

The voltage measurement can be taken at any unpainted metal on the positive terminal. You will see that it makes no difference - or if it does, then the nut on the threaded stud needs to be tightened.

If you decide to replace the battery, note that it is not necessary to remove the red plastic cover over the positive battery terminal. Just lift the cover up sufficiently for access to the terminal nut.

If you purchase the new battery from your local Toyota dealer, please take sharp photos of the top and side battery labels and post, if the new battery is something other than GS Yuasa, manufactured in Japan.

 

Don't know if you have an Advance Auto parts store by you but if you buy the Yellowtop Optima online there and pick it up at the store it was like $169 and you get an additional $50 coupon if memory serves me. Thats what I did and my new yellowtop has been doing very well and holding at 12.6 for almost a year now. It was a drop in.
If you go that route call ahead and ask nicely if they would put your new battery on the charger.
Sometimes these battery's sit on the shelf for a while and get depleted. That way you won't have to futz around charging it when you get home.

Brit likes the Exide and that seems like a better battery but not sure if it as available as the yellowtop in your region.