Turned the car on this morning after it sat for 3 days.

Radiator fans started running upon startup. This has happened before when the car "burped" after replacing the radiator. In the past a top off of about 1/8 cup of coolant/water mixture would trip the sensor in the expansion tank, and they would turn off. Tried this trick this morning and the fans did NOT turn off.

The radiator and the expansion tank were replaced recently, and no noticeable leaks have been detected.

Bad switch in the expansion tank?

What do you guys think? Thanks!
Brian

 

A/C button on? When I was testing my fans a couple of weeks ago, I noticed that one of them (only one is getting signal) came on when I depressed the A/C button right after startup, even though the engine was cold.

Hmmm... maybe my fan control module is my problem...

 

+1 on the AC button, fan starts even before engine.

It may have an outdoor temp override, many cars do, but typically it is in the 40's what was the outdoor temperature?

 

".... In the past a top off of about 1/8 cup of coolant/water mixture would trip the sensor in the expansion tank, and they would turn off. ..."

I didn't know that the switch in the expansion tank had anything to do w/ the Fans, thought it was only a fluid level switch?

 

That is correct Dave. The sensor in the expansion tank is just that - a sensor for fluid level - it is not a switch in the fan control circuit. The 4 sensor/switches in the fan control circuit are: radiator coolant temp, air intake temp (those two little wires on top of the intake), torque converter ATF temp, and high pressure AC refrigerant pressure.

Start with the troubleshooting section at the end of Vol. 1 in the WSM. There are checks for each sensor. Also have you been working anywhere else in the car ? Recently a thread where a guy working on a window problem was playing at the connections to his window controller - in one post he turns his fans on.

 

AC button is off. I know about that one.

Recent service included new radiator and expansion tank, and rear brake rotors and pads. It was running ok for a few weeks since those services were completed without problems, now this.

I'll check the WSM tonight.

 

Also the bottom slider isn't in the recirc position? Not sure which year started it but later models turn on the AC when in that position, even without the AC button pushed.

 

Good point.

 

Temperature switch on the bottom of radiator, unplug it and see if its still run when key turns.

 

^ Test function of all the sensor/switches from inside the car without getting dirty. Test at fan controller under front seat /passenger side panel. See WSM Vol. 1

 

+1.

This same situation - fans on at start-up - happened to me this summer.
After a little bit of search under the hood, I notice the slider was on the recirculation position.
Easy fix for sure!

 

Just a follow up.

AC button works and is off.

It was a bad relay IV or "ignition relay X". Second one from the left on the top row of relays.

Replaced with a new one and it works great!

 

Good of you to update for the sake of the Forum's knowledge.