Last night my alarm (honnking horn, lights flashing) went off when my 07 Prius was sitting in the garage with the garage door closed. The only way to stop the alarm was to start the car and leave it running. At 4:00 this morning it went off again. The only thing I can find amiss is that the battery icon on the main screen registered very low (two purple bars). Does anyone know anything about this phenomnon? Thanks, Azsaxguy
Strange happenings; lights going on and off, windshield wipers self- starting, etc, are frequently symptoms of a weak 12V battery. The battery has a typical service life of 4 years. This can be shortened by service in hot and cold climates. Should the car have to be jump- started, battery life is significantly shortened. If you have your original 12V battery it may be time to get a new one. Do you have any way to measure the voltage in your battery in the morning after sitting unused overnight? If so you want to see 12.5+V. Anything around 12V would argue for a new battery, hurry-up quick.
Thanks, I'll try it out. Unfortunately, I went out and drove it just now to charge up the main battery. And, it's Sunday so places to have it checked are few today. You said that having to jump it could lower battery life. Would using to jump another car have the same effect? I've used it three times to jump my Hylander hibrid.
You should not use a Prius (or your Highlander) to jump other cars (Jumping each other is OK as the current drain is low. NEVER hook them up backwards $$$). Each time you drain the 12v battery, it gets weaker. Three times or so and its basically gone. Note that the Prius 12v battery is not a standard one (It is vented and uses Japanese connectors). Only a Toyota dealer will have an exact replacement. A more robust replacement is the Optima Yellow Top (Model 51) which is available from: 12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007, 2008, 2009 and 2010 with installation kit With an installation kit (replacement connectors and a vent tube). JeffD
Re: Prius alarm goes off for no reason I agree that it is likely that your 12V battery is low. The same is probably true for your HiHy's 12V battery as well. Since it appears that you don't drive the HiHy enough to keep the 12V battery charged, I suggest that you periodically use a battery charger or else attach a battery minder. I bought a 12V battery for my 2004 last fall, from Precision Toyota in Tucson, for $138.70 plus tax. The old battery had not failed but I replaced it as a preventive move. I replaced the 12V battery on my 2006 HiHy last December, also as a preventive move. That cost $96.25 plus tax at Precision Toyota.
Do check that the rear hatch is properly latched. If it's not fully latched the switch could become intermittent and that will trigger the alarm. You can check your 12V system voltage using the MFD. Search on this site for the instructions. Or you can use a voltmeter on the boost terminal (under the hood, drivers side, fuse box - red flip-up cover). It's also possible the ground lead from the battery to the chassis is either loose or corroded. It's in the hatch under the floor on the right side.
12V battery check instructions here: http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html
