behind the battery box/tray
once you remove the battery and aformentioned you have to remove a heatshield on the back of it, be careful not to strip out those heat shield screws it is easy to do so. you will be able to recognize the ECU right away
oh, i dont know what negative side effects are, but there is a ground attatched to ECU - DO NOT FORGET to put it back one when you screw it back down inplace!!!!!