(I have searched for this problem, pretty extensively, and find no threads about it. Forgive me if I missed any.) My wife's 2002 Prius' battery was completely dead today (no lights, no locks, no response when ignitition was turned, literally nada), so I did a jumpstart according to the manual. I followed the instructions meticulously, though I did not detect anything different about the Prius method than any ohter. The instant that I connected the negative terminal to the trunk latch (recommended exposed metal ground), the horn on the Prius started going...constantly...and did not stop. I figured something was wrong, but I could find no infromation anywhere (except one question on Edmund's that was not answered with anything definitive or even specific) about this error. I plan to have it towed via USAA to the Toyota dealer tomorrow, but I figured I'd ask here in case it's a known problem. Thank you very much for any help you might provide.
Not a bad idea, but I'm pretty sure it was the map light left on, since one of the buttons for the forward right map light was depressed. <sigh> And I was the last driver. One speculation I heard was that perhaps this is the alarm going off? Is that normal?
My guess is that your car has an aftermarket alarm installed. If so, then as soon as you hook up the 12V battery and hear the horn sound, do whatever is needed to deactivate the alarm (typically, by using the fob's unlock button.) If my guess is wrong, then simply disconnect the horns (both are located in front of the radiator) so that you can drive the car until you have a chance to take it in for service. You probably have to remove the black plastic cover over the radiator to gain access to the horns.
