Drastic reduction in MPG 2008 - at 40,000 miles

As I'm sure you will hear from others, the 12v battery is the most common source of otherwise unexplained low MPG. If you have followed the testing procedures and the battery failed, I would have it replaced regardless of what the dealer said.
Hope you regain the faith in your Prius!

 

Anita,

I'm afraid that the folks at your service department don't know their
a$$ from a hole in the ground. These are classic symptoms of a bad
12V battery:

FWIW, failling/failed 12V batteries are probably the most common
problem with the Prius.

The 12V batter has a service life of ~4 years... if all goes well.

Fully discharging the puny 12V battery even once starts a rapid
downhill slide. To compensate for the dying battery, the HSD has to
divert more and more engine power to the High Voltage Battery which
in turn is converted to 12 power for all the little things that are needed
or used when you drive; computers and control units, lights, radio,
windows, etc.

I'll bet money that your 12V battery is very weak and if you don't do
something quickly, it may leave you stranded soon. A new battery at
the dealer should cost about $200 installed. There are other options
available on the "Net, but by the symptoms you've given, you could be
in a no-start situation tomorrow, vice the 4-5 days on delivery from
these folks:

12 Volt (12v) Toyota Prius Auxilary Battery for Prius with installation kit

Something to read:

http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html

Keep your chin up girl, this is most likely a very simple problem to fix. :cheer2:

[ame="http://www.youtube.com/watch?v=ZBR2G-iI3-I"]YouTube- I Will Survive[/ame]

 

Anita, please relax & suck down some of the free tea in the waiting room. 1. Trickle charge your existing 12v battery & keep an eye on it. If it won't hold a charge then you'll have to buy a new 12v sooner rather than later.
2. If it holds a reasonable charge then you're looking at buying a 12v battery later.

You can cut through some of the BS in the shop by either telling them to swap out the battery (skip the diagnosis) or buy the battery & DIY. You may find that quoting your voltages demonstrates that you have an idea of what's going on which will reduce the BS.

 

Sounds like maybe your 12V battery is bad. :madgrin:

 

2 1/2 years is short. Maybe the car don't get driven often?

Another thing to check is the battery connections in the trunk. Sometimes the problem is corrosion or loose connections. Good luck!

 

Check the voltages before leaving the lot. Often enough, fully charged batteries are not installed. Your new battery will have a 1 year unlimited mileage warranty.

 

If nobody has mentioned it I think your 12V battery may be bad....