my Hybird system did not start!

Check your 12V battery voltage. This sounds typical of a discharged 12V battery problem.

 

You're going to need a new 12v battery, so if you're not comfortable with replacing it yourself - might as well take steps to get that done. Its under the rear deck in the back passenger side corner.

Easy test: if the power windows won't roll down quickly, it's a dead battery. A jump will get you going, but READ the manual 1st on how to jump a prius.

 

A low 12V battery will cause all kinds of weird things to happen. Even though the car started it takes some time to charge the battery back up to acceptable levels (in the 12.5+ V range after sitting for a couple of hours).

Either take the car on a hour or longer trip or put a battery charger on the battery to fully charge the battery. If you continue to have problems with the monitor you may need to replace the battery.

If you are uncertain that you know how to correctly connect the charger to the battery you will need to take it someone that knows how. If you reverse polarity to the battery you can cause damage to some expensive electronics.

 

no, go to a toyota dealer.

 

The battery is not quite your typical lead-acid battery. A "conventional" lead-acid battery has little caps on top that can sometimes be removed; the idea that one puts in distilled water from time to time as the water gets used up during normal battery action. Such batteries give off hydrogen gas, which is one reason people are warned about not taking lit cigarettes or other burning objects near a charging battery.

Semi-new federal regulations state that if the battery is inside the body where people live, the battery (1) had better not give off much in the way of gases and (2) if the car gets turned over somehow that it not leak acid over people and other things. Hence, the Prius uses a glass-mat lead-acid battery. It's very thoroughly sealed, has a different interior (the glass mat), and is naturally, more expensive.

I might also add that the 12V battery in a Prius does not crank the engine; for that, the traction battery (the big one beneath the rear seat) is present. Instead, the 12V Prius battery basically boots the computers and such that make the Prius run.

However, testing such a battery is done the old fashioned way: One hooks up a battery tester to the terminals and, after looking up the settings for the battery tester for the particular kind of battery on has, the battery tester puts a load on the battery to see (a) how much current the battery will put out and (b) at what voltage. If the voltage and/or current are too low, the battery may need replacement.

I also note that a typical failure mode for any lead-acid battery is for a cell to short. Each cell in a lead-acid battery (there are typically six in series for ye standard car battery) has 2.1 V at nominal charge; six of them in series gives you 6 x 2.1 = 12.6 V. Charged all the way up one can get to 13.2 V; somewhat discharged, down to 11V and change. However, if one discharges a battery too far one can actually damage the battery. Say you have these six cells all in series and let the battery discharge. Given small random amounts of remaining charge, at some point five of the six cells will have a positive voltage and the weakest cell will have zero volts. A little more discharging will reverse the voltage on the weakest cell; after that, that cell may not take a charge any more. Then, instead of having a 12.6 V battery, one had a 10.5V battery. Further, the charging system expects to see a 12.6V battery, and will overcharge the remaining cells trying to get up to 12.6, further damaging the battery.

Low voltage on the battery will give the various computers inside the car the fits and result in strange, intermittent operation. For what it's worth, there have been reports on Prius Chat that dealerships have a bad time troubleshooting the issue. My guess is that they are so used to hooking up their computer automation that they can't even think of using a standard battery tester. Trying to get reasonable computer results out of computers that don't have enough voltage to run reliably is just as bad as it sounds.

You can get a replacement battery at a Toyota dealer; Optima makes a battery that works (checked Advanced Auto, they have it); Autozone sells a Duralast that claims to fit.

Replacing the battery is as straightforward as replacing any car battery. First, make sure it's bad by running the car around for 20 miles, then either sticking a voltmeter on it (with the cables disconnected) to verify that the voltage is up to snuff (if it's below 11V, it's a goner) and/or taking it to a place like Autozone, which will test it for free. If it's bad, buy a new one, get the old one out, put the new one in, put the usual goop/felt battery washers on to retard corrosion, and put the cables back on. If you've never done it before and don't have the tools and/or inclination, any auto repair facility can do it. Although most mechanics won't have this type on hand, which is why Toyota, which will have one on hand, may be a better bet.

Good luck!

KBeck

 

Great explanation. I learned quite a bit. Thanks.

 

if his car gets to Ready it no longer matters how much the 12V battery is charged (until next startup of course) ALL 12V systems are powered by the DC/DC converter fed by HV battery

 

You are making the assumption that the battery is charging properly. The battery can have shorted cells and be pulling the DC/DC converter voltage down.

 

Agreeing with you here, but with a slightly different take: The DC/DC converter may actually be putting out the charging voltage, and the battery may actually be (over)charging to that voltage, but, once the car is out of Ready and the DC/DC converter isn't running, the battery would then drop to Something Lower Than Expected.

Like Clinton, it depends upon the definition of "short".

KBeck