My auxiliary cooling fan runs constantly when the engine is on and often runs after shut down but usually shuts off eventually. Recently, the fan doesn't shut off at all and I have to unplug it. Any ideas on why that would happen? Maybe a bad sensor? If so, does the temperature sensor at the bottom of the radiator drive this fan?
Thank you.

 

The fan is controlled by the ECU, which processes data from either the Coolant Temp Sensor, or the HVAC control module. I would suspect the relay is sticking/stuck. You can start by pulling the relay and swapping it with a similar relay. Here's the layout in the engine compartment fuse box. #3 or #8 look like good candidates to use if you have them.

 

I'll give that a try. Thank you!

 

That seems to have worked. Now I need to find a local source to replace the relay. Thank you so much!

 

@NVDiscovery they are pretty common relays

 

BTW, in changing all of my relays R6 runs my SAI and O2 sensors. I initially left it out thinking that I didn't need to replace it (glow plugs) but through a code. I cleared the code and then re-installed a relay and all is well. Still not sure if R7 runs anything but it was there in stock form. Ideas? Also, my relays are all 4 pin. The yellow relays are marked Ford and the black relays are marked BMW and have a wider front slotted pin.

 

[QUOTE=ahab;809106]The fan is controlled by the ECU, which processes data from either the Coolant Temp Sensor, or the HVAC control module. I would suspect the relay is sticking/stuck. You can start by pulling the relay and swapping it with a similar relay. Here's the layout in the engine compartment fuse box. #3 or #8 look like good candidates to use if you have them.

[/hi. I am not mechanically minded. When I swap say #3 out, swap it with what? Where does it go?QUOTE]

 

Relay R4 is the cooling fan, if it's stuck then the fans will continue to run. Relay R3 is for the headlamp washers and relay R5 is for the self-leveling system. They are all the same type of relay. If your fans are staying on because of a bad relay, but your headlamp washers or self-leveling suspension work correctly then you can remove one of those other yellow relays and swap it into the number 4 slot to see if the fans work correctly. If nothing changes then you problem is not the cooling fan relay. You cannot use R1 or R2 because those are needed to start and run the truck so don't try those. The truck will run fine if you use the others but you won't have headlamp washers or self leveling while you test. This should not be a problem.

 

I replaced all of my replays since they appeared to be the original units. Also, I changed out the radiator, t-stat and temperature sensor. Issue seems to be resolved. Thanks for everyone's input!

 

Hello, I'm having the same issue. I need to unplug the fan as well. Can you tell me how and where to unplug the fan?
Thank you.