Weird stuff happening? MPGs dropping? Test The Battery

I would replace it at the first hint of trouble, you may wish to find a local shop so you aren't in a panic, or you may wish to be sure the Toyota dealer has one in stock, as Toyota's warranty is very good.

 

12.4 is a fine voltage. I would keep using that battery.

Do you do much short trip driving? If so just charge it with a ctek 3300.

If not keep checking the battery every few months and replace it when that floating voltage is closer to 12.0v.

 

This is AWESOME information!!! I'm on my 2nd Prius and I never knew this about the first one. Now I want to learn what else I can check out without spending a fortune.
Thank you sooooo much!

DO-IT-YOURSELF TEST PROCEDURE (thanks to jdenenberg):

 

welcome to priuschat! all the best.

 

Just recently purchased a used 2008 toyota prius with 110,000 miles and i'm noticing a mpg drop. The previous seller (which I may have come to a conclusion that he might of flipped the vehicle) had prior records of the car being serviced at a toyota dealership from the first owner since it was new. He then admitted to me that he replaced the 12v battery. After following the steps I got a mark of 12.5 unloaded, current load of 12.3, and a ready of 14.0. Does that seem fairly accurate if he did replace it?

 

So today I got the red triangle, brake warning light, and vsc light. The car was lethargic and would barely go anywhere. Eventually it all cleared up and went back to running normal. But the lights stayed on even after I reset them with my code reader. No codes came up though. So my voltages are pretty low as well, by doing this method to test the, so I took the car to O’Reillys auto parts and they said the battery tested good. They did say my starter failed the test. Do y’all think it could be causing these issues or do you think the battery is dying and that’s the issue?
Unloaded 12.1
Loaded 11.9
On 13.9

 

Yes, way too low.

 

Hi ,

This is a really long thread ... it may be that somewhere way up there, one particular method was mentioned, but just to make your post more self-contained, could you say what method you used to check your voltages?

Some of the common methods on PriusChat will consistently read over half a volt lower than others, which you can see would make all the difference between the numbers you reported being somewhat low or quite robust.

-Chap

 

The Prius does not have a 12 volt starter.

I would replace the battery, and in fact I am, as I recently saw 11.9 volts on my ScanGuageII

 

A Solar BA5 (DIY level electronic load tester), connected direct to the posts, car off, would give a better picture. I would think O'Riellys would have used a pro version, similar tester.

 

OK, so the last posting on this thread is 2 years old. Is there a DIY procedure that works on a 2020 Prius Prime?

 

I have no direct experience with the Prime, but a simple variation on the 12v battery test That I developed in the early days of the Gen2 Prius should work. I'll assume that you have access to a digital volt meter:

1. BATTERY HEALTH - After your Prime has rested overnight and while it is still in the OFF state what is your 12v battery voltage?
   • If it is over 12v, go on to step 2
   • If it is under 12v, you probably have a problem. Either the battery needs replacement, or it was not sufficiently charged before beginning this test, or the charging system does not put out sufficient voltage. Go to step 3 to test the charging circuit.
2. LOAD TEST - Put your Prime into Accessory mode (Press the power button once without stepping on the brake) and turn on the parking lights. the voltage should not drop below 12v due to the load on the battery. Push the power button twice (without stepping on the brake) to get back to OFF and the battery voltage should recover. If the voltage drops noticeably and does not recover to almost it's earlier value, consider replacing the battery.
3. CHARGING TEST - Now put your Prime into RUN mode to turn on the charging system. The 12v battery voltage should go up to about 13.5 volts and not over 14 volts if the charging circuit is functioning correctly.

Note that the charging circuit in a Prius is a slow constant voltage system and it takes a significant amount of time to recharge a depleted 12v battery. I hope that his helps.

JeffD

 

GOOD STUFF !! This is an excellent check, assuming you have a voltmeter.
What I really wanted to know, however, was how to get the 2020 Prius Prime into maintenance mode.
The procedure for previous year models didn't seem to work on my 2020 Prime.

 

How do I say this without sounding snobby? As far as I know, if the Prime has a maintenance mode shortcut, no one has talked about it yet.
Since no one has talked about it yet, I'll suggest getting into it, if it does exist would be an unofficial hack. A good one, but since it's unofficial a hack non the less.
Lets raise out glasses (with whatever you perfer to have in it) and toast to someone eventually finding a combination of button presses and other wizardry that actually runs the car in test mode.
Here are the unofficial instructions for silencing the beeping while in reverse Hybrid Car – More Fun with Less Gas » Blog Archive Backup Beeping on Prius
Cheers.

#jdenenburg Thanks for posting your thresholds and procedures. I've already used some of them and will be posting my baseline reading in rob43 's thread 12v Battery Is Discharging, Re-Charge Now ! | PriusChat

 

T

 

It's nice to be remembered for a post in 2004.

JeffD

 

Thank you for posting this battery checking procedure. I know I used it probably in 2012 or 13 when I replaced the battery in my 07 Prius it with the Optima Drop In. My wonder car has 189000+ miles and outside of recalls for water pump, steering shaft, combo meter /dash lights it has only needed maintenance. That is until this winter when the Triangle of Death popped on. Turned out to show code for EGR. I couldn't afford to take it in so I drove it without further problems until last week. Suddenly as others have stated my lights lit up with everything from VSC to ABS etc. I had to pull over and let the car sit then I could drive again. After researching on Prius Chat found this and checked my battery as you posted in easy to follow steps. After sitting all night 12.1, with load AC and lights 11.4. Time for a battery which is being done this afternoon. Putting in the AC Delco as recommended in PC.
Hoping this will take care of the problem so I can at least drive. I will ask this repair shop what other repairs they do on Prius and then tackle EGR etc.
Here's hoping it is only 12v battery!
Thank you again!

 

If this is second gen Prius (last model year 2009) then you shouldn’t have Exhaust Gas Recirculation problems. I believe second gen has rudimentary EGR but not trouble prone. It’s third gen has EGR problems.