Entering Maintenance Mode (aka 12V Battery Check) without Switching Headlights ON/OFF

Thanks. Car wasn't driven for two days when I checked it. I will check it again on Friday after I do a 2 hour drive. Car becomes 5 years in August, so I want to wait until then if possible.

 

If you want to be a good mommy to Pria order the battery today so you'll have a birthday present for her

 

Definitely. She gets new shoes in August too!

She is getting a dent fixed today and being detailed/bumper refinished tomorrow.

 

Checked immediately after driving for 2 hours and it was 12.3V.

 

I find a charger (or two) and a digital voltmeter very handy.

 

I know, you said earlier to do that, but I forgot to come back after a couple of hours. I don't think I had the headlights on when I checked, but had them on during the 2 hour drive. I will do it right at some point. Thanks for your help.

 

Burnselk: Simple suggestion to improve mileage. Do the speed limit and use cruise control. BUT: is she ready for that?

 

What does "Now test the battery with some load" mean? When I press the power button again without stepping on the brake, the screen changes from the Vehicle Signal Check Mode screen back to the opening screen that looks the same as what it always does when I pressed the power button the first time.

BTW, this is on a 2005 Prius with the built-in Navigation System. The voltage level on mine reads 10.0V without the headlights on (see camera snapshot of it at screenshot). That leads me to be believe it is time to replace my battery, because I am seeing the same start-up weirdness as reported in another post. I've recorded the issue with my Android phone and uploaded it to Prius 2005 Transmission lock is abnormal - YouTube and also uploaded a video showing what I have to do each time to workaround it at Prius 2005 Transmission lock is abnormal workaround - YouTube

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Turning on the headlights is plenty of load. But if yours is 10V when you first walk up to it with no load then it's near death already. Replace it immediately. Any day now the workarounds will stop working and you'll be stuck somewhere.

 

Great advice. Thanks Richard!

 

The info in this thread is very good. Simple and accurate. I would do both tests as they really check out different problems. A battery can be ok once charged but have much reduced capacity. There could also be a higher than normal current drain or the battey could lose charge quite quickly. It depends how often you use the car as to how critical capacity is as the battery is being charged all the time the car is in Ready mode.

It is probably a good idea to replace the battery after 4 years. My car is 4 years old and I think the capacity is down to 10AH.

The charge current on any battery being charged at a fixed voltage is defined by the Battery not the charger. Good batteries will take more current at 14V than old batteries which is why they charge slower. (For the same state of charge)

 

How do you get out of this mode? Does pushing and holding the display button do enough?

 

So far I think the only known why to exit this mode is to power the car off (and back on again if required). That's the way I do it.

 

That's how I do it. Press and hold the display button for more than five seconds and you'll see the start up screen. You can then let go of the display button and the radio will come back on (if it was turned on) and you're back in the normal display.

 

I just checked the reading on my 07. Right after driving I got 12.5v no load, down to 12v when headlights on.

My concern stated the other day when the car wouldn't start. I think I didn't get the hatch completely shut the night before. No cabin lights on, though. The headlights seemed a bit dim as we tried to figure out what was going on. I think turning off the headlights is what allowed the car to finally boot.


Any one care to guess with me how close to end of life my 12v battery is?

 

It's never a good idea to try and start any car with the headlights on. Start the car first, put headlights on second.

12.5/12.0 is ok, but it's a much more telling test if you do it after the car has been off for several hours or more.

I like to do the test in the morning after the car's been off overnight. I like to bring it to "acc" mode, turn off all accessories (radio fan demister etc) and then enter the service menu to get a "no load reading". This is typically 12.3 volts for my battery but ideally would be slightly higher for a newer battery.

Then I press the "on" button one more time to get to "Ig On" mode and record the second "under load" reading. Still no accessories, but the load is due to running all the ECU's etc. This is typically 11.9 to 12.1 volts for my battery, but a again a few point higher would be more typical with a newer battery.

Finish the test by pressing the brake pedal and "On" one more time to get ready mode. The DC-DC converter is now charging the battery and the voltage should be around 13.8 to 14.2 volts. This doesn't really tell us too much about the battery but ensures that the charging system is working correctly.

 

I wish I'd seen this a week ago.
Thanks for the extremely useful post.
I like the idea of secret buttons also.
Will try this later today.