[jdenenberg]

You can easily check out your battery status/charging system using the MFD in maintenance mode. No tools required.

1. Get your Prius into "Accessory Mode" - Press the power button without touching the brake pedal.
2. Put the MFD into "Maintenance Mode" - Press and hold the "Info" button on the MFD while turning the headlights on and off 4 times.
3. Press the "Menu" field on the screen.
4. Press the "Display Check" field.
5. Press the "Signal Check" field.
6. The 12v battery voltage will be one of the items listed, it should be above 12 volts. If it is lower, either the battery needs replacement or the charging system is not functioning correctly - see step 7.
7. Put a small load on the battery by pressing the power button again without touching the brake pedal. The voltage should stay above 12v. If it drops significantly, you need a new battery.
8. Now get your Prius into "Ready Mode" - step on the brake and press the power button. The battery voltage should immediately rise to 13.8 volts (Your Prius uses constant voltage charging). If it is lower, the battery will never charge; if it is much above 14 volts, your 12v battery will get cooked.
9. Shutting the car down will reset the system back to normal operation.

If you need to get a new 12v battery, you can opt for a dealer replacement or get a better battery at a lower price at: http://www.elearnaid.com/12vo1topraub.html
and install it yourself.

JeffD

[centrider]

jdenenberg said:

you can easily check out your battery status/charging system using the mfd in maintenance mode. no tools required.

1. get your prius into "accessory mode" - press the power button without touching the brake pedal.
2. put the mfd into "maintenance mode" - press and hold the "info" button on the mfd while turning the headlights on and off 4 times.
3. press the "menu" field on the screen.
4. press the "signal check" field.
5. the 12v battery voltage will be one of the items listed, it should be above 12 volts. If it is lower, either the battery needs replacement or the charging system is not functioning correctly - see step 7.
6. put a small load on the battery by pressing the power button again without touching the brake pedal. The voltage should stay above 12v. If it drops significantly, you need a new battery.
7. now get your prius into "ready mode" - step on the brake and press the power button. The battery voltage should immediately rise to 13.8 volts (your prius uses constant voltage charging). If it is lower, the battery will never charge; if it is much above 14 volts, your 12v battery will get cooked.
8. shutting the car down will reset the system back to normal operation.

if you need to get a new 12v battery, you can opt for a dealer replacement or get a better battery at a lower price at: http://www.elearnaid.com/12vo1topraub.html
and install it yourself.

Jeffd

geekers willikers! What a gem!

[Smiling Jack]

jdenenberg said:

You can easily check out your battery status/charging system using the MFD in maintenance mode. No tools required.

1. Get your Prius into "Accessory Mode" - Press the power button without touching the brake pedal.
2. Put the MFD into "Maintenance Mode" - Press and hold the "Info" button on the MFD while turning the headlights on and off 4 times.
3. Press the "Menu" field on the screen.
4. Press the "Signal Check" field.
5. The 12v battery voltage will be one of the items listed, it should be above 12 volts. If it is lower, either the battery needs replacement or the charging system is not functioning correctly - see step 7.
6. Put a small load on the battery by pressing the power button again without touching the brake pedal. The voltage should stay above 12v. If it drops significantly, you need a new battery.
7. Now get your Prius into "Ready Mode" - step on the brake and press the power button. The battery voltage should immediately rise to 13.8 volts (Your Prius uses constant voltage charging). If it is lower, the battery will never charge; if it is much above 14 volts, your 12v battery will get cooked.
8. Shutting the car down will reset the system back to normal operation.

If you need to get a new 12v battery, you can opt for a dealer replacement or get a better battery at a lower price at: http://www.elearnaid.com/12vo1topraub.html
and install it yourself.

JeffD

Anyone know whether same procedure works for Camry?

I may try.

And: Are we sure that 15 v. would be too much. A lot of aux. auto battery chargers would do 15 v.

[jdenenberg]

Smiling Jack said:

Anyone know whether same procedure works for Camry?

I may try.

And: Are we sure that 15 v. would be too much. A lot of aux. auto battery chargers would do 15 v.

1. There is a good chance that a variation of this procedure will work on a Camry Hybrid, Highlander Hybrid, or Lexus Hybrid as Toyota tends to be consistent.

One reported alternate sequence to get to the Maintenance screen is a sequence of screen touches:
"Push DISPLAY and then instead of Upperleft, Downleft,Upperleft, Downleft,Upperleft, Downleft try Upperleft, Upperright, Upperleft, Upperright, Upperleft, Upperright."

Report your results back here.

2. 15 volts WILL cook a AGM Lead Acid battery in this case as there is no protection from overcharging the battery. A good charger reduces the voltage as the battery reaches full charge, the DC-DC converter in these hybrids is not that smart. Note that even 14 volts continuous is not good, but the charging circuit is only active in "Ready" mode. For continuous battery maintenance get a "Battery Minder" or Battery Tender" as these systems use safe continuous charging methods. They will safely maintain the little 12v battery when the car is left unused for a long interval (more than 2 weeks).

JeffD

[geodosch]

Jeff,

That's great info to have! Once difference, at least on my '07 Prius, is that after pressing [Menu], I had to first go to [Display Check], and then to [Vehicle Signal Check]

[jdenenberg]

geodosch said:

Jeff,

That's great info to have! Once difference, at least on my '07 Prius, is that after pressing [Menu], I had to first go to [Display Check], and then to [Vehicle Signal Check]

Thanks for the corrrection. I edited my original post.

JeffD

[chicagowinter]

jdenenberg said:

One reported alternate sequence to get to the Maintenance screen is a sequence of screen touches:
"Push DISPLAY and then instead of Upperleft, Downleft,Upperleft, Downleft,Upperleft, Downleft try Upperleft, Upperright, Upperleft, Upperright, Upperleft, Upperright."

Report your results back here.

Jeff,

On my 2007 Prius, the Info + cycle-headlights method fails to enter maintenance mode. The display does reboot, but it returns to the normal display rather than to the maintenance menu. On the other hand, the Display + touch-sequence method does work, using the sequence UL-UR-UL-UR-UL-UR. Thanks.

(BTW, this reveals my battery voltage to be only 9.6 V, presumably explaining recent failures to start. Is three years a normal time to failure for the auxiliary battery?)

[jdenenberg]

chicagowinter said:

Jeff,

On my 2007 Prius, the Info + cycle-headlights method fails to enter maintenance mode. The display does reboot, but it returns to the normal display rather than to the maintenance menu. On the other hand, the Display + touch-sequence method does work, using the sequence UL-UR-UL-UR-UL-UR. Thanks.

So Toyota makes changes from year to year. This shouldn't surprise us.

(BTW, this reveals my battery voltage to be only 9.6 V, presumably explaining recent failures to start. Is three years a normal time to failure for the auxiliary battery?)

Our Prii use a "Constant Voltage" charging protocol. This is a simple way to ensure that the 12v battery is never overcharged, but also means that the charging is very slooooow. If you regularly drive your Prius for long drives, this system does a reasonable job of maintaining the 12v battery at full charge (My 2004 at 168k miles is still on it's original 12v battery). If you drive a short commute, the battery will tend to discharge and lead-acid batteries require storage at full charge or they will fail prematurely.

One way to maintain any 12v battery in good health (if you have access to a 120v outlet) is to use a Battery Minder in your garage. The one to get is:

http://www.batteryminders.com/batter...--p-16151.html

It is about $60.

JeffD

ps. A Battery Minder may revitalize your existing battery if it is not too far gone.

[centrider]

Thanks for laying out the means to check the battery. I have an'06 with 60,000 + miles on it. Mon. I went out and followed your instructions and found the battery was 11.8 (truthfully, the car sits in the garage for such extended times I get to fill it every other month).

When I started the engine, the charge went up to 14. Driving the car so infrequently in our, "winter" I guess doesn't drag it down as it would if I were driving it a Chicago winter.

[dddrrr]

jdenenberg said:

You can easily check out your battery status/charging system using the MFD in maintenance mode. No tools required.

1. Get your Prius into "Accessory Mode" - Press the power button without touching the brake pedal.
2. Put the MFD into "Maintenance Mode" - Press and hold the "Info" button on the MFD while turning the headlights on and off 4 times.
3. Press the "Menu" field on the screen.
4. Press the "Display Check" field.
5. Press the "Signal Check" field.
6. The 12v battery voltage will be one of the items listed, it should be above 12 volts. If it is lower, either the battery needs replacement or the charging system is not functioning correctly - see step 7.
7. Put a small load on the battery by pressing the power button again without touching the brake pedal. The voltage should stay above 12v. If it drops significantly, you need a new battery.
8. Now get your Prius into "Ready Mode" - step on the brake and press the power button. The battery voltage should immediately rise to 13.8 volts (Your Prius uses constant voltage charging). If it is lower, the battery will never charge; if it is much above 14 volts, your 12v battery will get cooked.
9. Shutting the car down will reset the system back to normal operation.

If you need to get a new 12v battery, you can opt for a dealer replacement or get a better battery at a lower price at: http://www.elearnaid.com/12vo1topraub.html
and install it yourself.

JeffD

Hello Jeff ,Once I pressed "Menu" then "Displaly Check"field then "Signal Check"field my reading was 12.1V. When I pressed the power button again it dropped to 11.8V Then I went to "Ready Mode" and it read 14.3V then droped to14.2V then to 14.1. Do I need a new battery or is the Charging system not working properly?
Thank you very much for your help