My engine fan was doing the same thing. It kept coming on at random times, even when the car had been parked and turned off for hours. I would constantly come out to a dead battery. I took it to an electrical shop that did a fuse search and found a draw with #5. #5 controls: turn signals, hazard lights, A/T control unit, Automatic seat belt control unit and the PGM-FI ECU. The mechanics moved everything from the #5 fuse from "automatic" to "accessory." This way, the fan does not come on automatically. The downside is that you have to have the key turned in order to operate the other components like seat belts, hazards.