All brake warning light came on when the 12v battery died - yellow line to wheels on when stopped

Not only possible but very likely that the battery is the only problem.

Get it fixed FIRST.......and SOON. It may die on you the next time in a dangerous situation.
Scanning for codes with a failing 12 V battery is just a waste of time.

Charge the new one fully before installing.
Then check the charging voltage with the car running.

 

Steps to take:

1. Check the 12 volt battery's voltage, with the car off, first thing in the morning, with a digital mulimeter. Compare to this chart will give you an idea of it's status:



(For a more in-depth assessment, DIY load test yourself with something like Solar BA5, or get it to a battery retailer with electronic load tester, see what they say)

2. Attempt charging, with a smart charger in the 3~4 amp range, see how that goes. A Solar BA5 for one will give an assessment, and also say if it's even worth attempting to charge.

3. Skip step 2, especially if your multimeter voltage reading is around 12.0 or lower, go straight to battery replacement.

 

Better yet, use the built in battery test.
https://youtu.be/cFaHKKx4mME

 

When using the Vehicle Signal Check screen to gauge battery condition, if you're comparing it to a voltage chart like the one Mendel posted, don't forget that reading tends to be a significant fraction of a volt lower than what you would see with a meter at the battery terminals, and that's if you do the test in ACC. If you do it in IG-ON (as in Carolyn's video), with more of the car being powered up, it will be lower yet.

That doesn't mean the method is unreliable; once you've learned what the voltage difference is, it's pretty consistent, so if you just add it back to what you see on the signal check screen, you'll get fairly close to what you'd find by digging out the hatch stuff to measure at the battery. In ACC, anyway. In ON, there is more variation of what parts of the car are drawing power, so more variation in the reading.

-Chap

 

Yes, that is normal.

 

Is that using the car's displays, not a multi-meter? No clue what the fudge factor would be. Maybe get your hands on a multi meter?

12.2 volts with the car off, with a multi-meter, would be ominously low, fwiw. Anything under 12.5 volts would be setting off alarm bells for me.

FWIW, our car sits multiple days sometimes, and I just hook up a smart charger, leave it permanently connected, no problems.

 

The chart above says it is at 60%. In the green. OK, but not totally full.

You may actually have a brake problem.

 

low, sometimes new batteries need a charge before installing. if you don't have a charger, leave the car in ready for a few hours at a time, and check the voltage in between.
a new battery should get close to 13 volts.

once you know the battery is charged, if the lights don't go out, you can start hunting for the problem.

 

You said that the battery has been charged.......but then what you say after that makes it sound like you don't KNOW that for sure.

IF......you have not manually charged the new battery, do that. Then leave it disconnected for a half hour or so.
If that does not clear the codes you REALLY need to get it to a shop for a diagnostic (reading of codes and resetting with the tool).

Continuing to make wild guesses here might be interesting but likely that it will NOT be productive.

 

This is a quote from another user here at this forum, so this is a copy not a theft. When I replaced the master cylinder in a gen 3 I had to do this same reset to clear the codes. If they come back, you need to address the problem.

Find the can 2 bus link/ OBD2 port under the dash below your right knee.When looking up at it you will find a connector with 2 rows of 8 pins each. Connect a jumper between pin 4 (CG pin) and pin 13 ( TC pin) on the OBD2 connector. Starting at the top row reading from left to right, pin 4 would be the pin 4 pins away from the left on top row. On bottom row pin 13 would be 4 pins from the right on bottom row. Connect the two pins using a small paper clip, then put the car into ready mode. It will start blinking the ABS light on the dash and the touch screen display will not look normal. Press the brake pedal 8 times or more in 5 seconds after turning the car into ready mode. Turn off the car and remove jumper. The ABS light will not be on. This procedure only resets the light, not the underlying problem. If the original fault is not repaired the light will come on again

 

with that driving scenario, you might want to invest in a battery maintainer.

 

Good call on the smart charger tip. I think it's time to invest in one of those. Any particular brand / model you recommend and or have had a good experience with?

Also, just like the OP I have the ABS, brake system lights that popped up on the dash during my low voltage issue. I've read that the brake module that sets these lights is sensitive to the low voltage situation caused by a weak 12V battery, so...

how do you recommend clearing these lights? I tried an OBD adapter in combination with the old Torque app, but of course it couldn't clear ABS codes.

Thanks!

 

I’m using a CTEK 4.3, works well. Price has been climbing though, maybe supply and demand with a lot of sidelined vehicles due to COVID?

 

Okay cool I will check that one out, any thoughts on the second part of my inquiry?

Posted via the PriusChat mobile app.

 

Not sure.