2009 g37 coupe - 55k miles

So my radiator fans will come on when the car is in the on position and engine not running (and cold), and they will stay on all the time, until the car is shut off. Both the fans come on, even without the a/c on. I bought the car from an auction and had to replace the radiator fan cause it was cracked. Radiator survived. There was only 2 plugs when changing the fan out, I made sure those were connected properly. I've read online to check relays and fuses, idk how to visually check a relay, but the fuses are fine. My next guess is the Temperarure Sensor? Although I know this information is all online I also noticed my MPG is acting weird, and I'm not sure if these two problems are related. If I reset my mpg wile driving it seems normal, I was getting 29 mpg on the freeway when on cruise control for 65mph. The problem is everytime I shut the car off and start it again, letting it warm up, the avg mpg will drop 4-5. It will continue doing this. I've gone from 29 down to 12 mpg? I'm not sure if it's going to go lower than 12. Is my reading incorrect? Or is my car dumping too much fuel at start up or idle? Does this have anything to do with the fans running all the time?
Any help/advise is appreciated, thanks.

 

Sounds like this might have been a flood vehicle?
Have a dealer run the VIN number and provide a history of this vehicle.
Does it have a washed/salvage title?
Originally purchased in another state from where you are located?

Telcoman

 

I live in California, the car has spent all its life in Arizona (where it was purchased from). History did not show any water/flood damage, I also can't image that being the case coming from AZ. It had light front end damage, mainly to the lower section. The front lower subframe bar was slight pushed up into the radiator and cracked the radiator fan. There was no damage past that front subframe bar. Hood was fine, both fenders were fine, front bumper still has all mounting points but it's very scratched/dented up. Driver airbag deployed. That's the extent to the damage, if the airbag had not deployed I do not believe they would have salvaged this car.
The car was listed for sale at a dealership less than 1000 miles ago. That being said I don't believe this fan problem existed before the accident.

 

Flash floods close roads, strand drivers in Arizona
Published August 03, 2016 Associated Press


http://www.foxnews.com/us/2016/08/03...n-arizona.html

There is a reason an insurance company declares a vehicle salvage.
Accident, floods, or both. Not worth repairing.

Telcoman

 

Thanks for the info, but there are no signs that my car has been in a flood. And there's no other problems with the car besides the fan staying on all the time and mpg recording.

 

You can't really check a relay by looking at it, unless it's obviously messed up. Best method is to supply power, hear it click, and then test the other contacts for continuity. Not sure on the 09, but on my 06 coupe the IPDM is behind the battery and there are two relays in there that control the fan.

If they are turning on then, I would most likely say your relays are fine. I would start with your coolant sensor like you mentioned. Read the FSM and see if there is a resistance spec to see if it's bad or not. Pull up a wiring diagram and see what else is in that circuit that could make them be turning on.

If you temperature sensor is bad it will affect your MPG. The car will think it has to remain in open loop mode and never get into closed loop.

I'd put a scanner on there and see if it's going in closed loop, temperature, etc...

It could be a bad ECU, IPDM, or something like that as well.

 

Also, is your AC compressor running all the time even when it's supposed to be turned off? AC on will trigger the fans to blow even when it's below temp. Could be a faulty AC switch, running the compressor DEFINITELY affects fuel economy.