What is a coolant spoofer you might ask? Well the Prius goes through 4 warm up stages before you can get it to turn off the engine every time like you'd like to do. Most of the stages are controlled by the coolant temperature. So, this little circuit tells the ECU that the engine is warmer than it really is to get you through the warmup process quicker. Also, if you have the heat turned on in the Prius, depending on the coolant temp, it will keep your engine running or not. So, the coolant temp spoofer basically allows for more engine off operation.
The coolant spoofer I got was from ccdisce over on Priuschat. Its a custom board he designed to do the job, and he now sells them.
Here is the kit contents.
Here is the little tiny spoofer board. Its only about as wide as a quarter.
To install it you remove the glove box to access the ECU wiring behind it. You only have to hook up three wires: power, ground, coolant temp. So, its very simple. Mine was even easier because I already had the wires hooked up to wiretaps from the arduino board.
Here we go, all "installed". It'll probably stay that way just giving company to my EV switch and ipod.
I only just installed it on Thursday night (2 days ago), but I did notice on the way to work on Friday I was able to get my engine to shut off earlier than before. I'm not sure how this will translate to mpg, but at the very least I should be able to use my heater a bit more in winter and that would be quite nice.