Last Tuesday the battery in my girlfriend's 2007 RDX died. The parts store said the battery was shot so we bought a new battery. As soon as i hooked it up the cooling fan came on but I didn't think anything of it. The next morning her battery was dead. Just the drivers side cooling fan, not both. On Sunday, I got the battery charged and got a new fan control relay figuring the relay just went out. Replaced the relay, hooked up the battery and it was money. Monday the car ran fine. Tuesday we didn't drive it much but late that night I took it out and when u got back the fan stayed on. I disconnected the battery so it wouldn't kill it, and hooked it back up the next day and the fan immediately comes on without me even having the keys in the car. Anyone have any ideas?

 

If all fan fuses and relays check out, and this is a shot in the dark, but maybe look at the coolant temp sensor/harness/wiring? If the coolant is above a certain temp, fans may come on even when the car is off. If the sensor is reading incorrectly or not working, car may have fan on as a precautionary measure.

 

Try replacing the "other" fan relay.

Or when the fan runs on start pulling relays untill you find the right one. Then swap it with a known good relay from the same car. If the same fan stops working the you'll know it's a defective relay.