My '08 Ford expedition has been having cooling problems. I put it aftermarket fan clutch in and for some reason it seems to only engage during the first few minutes of cold starting the engine. I don't know if I should blame the aftermarket product or if the ECU is going bad... Any thoughts? Thank you!
2008 Ford expedition
226K miles
Since the fan runs at startup, if you look how the fan wiring connector is wired, you know you're getting power on Pin 2 (YE-GN wire).
You know that the PCM can send a Pulse Width Modulated ground on Pin 6 (BU-BK wire) to control the fan speed.
That just leaves the 3 wires for the Hall effect sensor.
Inspect that wiring connector for corrosion or damage and while you have it disconnected make sure there's a Ground on Pin 5 (BK-GN wire).
Then you can check the remaining 2 wires for breaks, chafing, or shorts to Ground.
Usually with these electrically activated viscous fan clutches if there's a circuit issue the PCM will set a code so you may want to hook up a scanner and check
With wire colors! Thank you!
Excellent, thank you very much!
Here's what I found:
Fan signal speed 12 volt
(Green/yellow stripe)
Power distribution 14 volt
(Yellow/green stripe)
Fan motor control 0 volt
(White/blue stripe)
Voltage reference 12 volt
(Green/violet stripe)
Ground 0 volts/perfect continuity.
(Black/green stripe)
Well the Fan Motor Control is a Pulse Width Modulated Ground from the PCM to control the Fan so you'll either find "Open" or Ground there, never voltage (Pin 6)
.
You've determined that you have battery voltage from the PCM Power Relay (Pin 2)
.
You have Ground from Ground Point G107 (Pin 5)
.
You have 12 volt reference voltage from the PCM (VREF) ((Pin 3))
.
So now on Pin 4 (Fan Speed Signal), ((GY-YE wire)) Key ON, fan wiring connector connected and the GY-YE wire back probed at the connector, as you spin the fan slowly does the voltage go from 12 volts to 0 volts?
Your best final test is to back probe the fan connector Pin 6 (BU-BK wire) ((fan connector connected)) start the truck and run a jumper wire from Ground to that back probe. That will mimic a 100% duty cycle from the PCM and the fan should turn at its fastest speed if the fan is good
I don't think meters are that fast. Most likely it'll average out (RMS) the PWM signal and read some voltage between 0 and 12.
I think if he turns the fan slowly by hand he'll see the voltage drop out and return
I think the PWM signal just pulses an electromagnet, pulling the clutch in. Spinning the fan won't generate any voltage on the clutch control pins.
Yeah but I'm not asking him to test the PWM Ground signal from the PCM to control the fan speed
.
I want to know if the Hall effect sensor in the fan is working right
ohhhhh yah. you're right . My bad.
and it's not even an EM clutch. It's viscous. I'll shut up now. 😳
No problem, Joe. Chevy and Chrysler controls these electrically activated viscous fan clutches on the Power side using a PCB relay pulsing power to the fan clutch
.
For some reason Ford decided to use the PCM to control the fan clutch using a PCM provided PWM ground
.
The circuit is confusing to say the least
I'm not sure if you all will see this because it's been a little while. I tested the voltage of the fan speed signal and what I noticed is that every few inches I would rotate the end of the fan blades the voltage would go from near zero to near 12 and then back and forth. So my conclusion would be that the magnets of the fan motor are determining the voltage signal.
Yeah, you've determined that the Hall effect sensor in the fan is working
.
So now like I said, did you back probe the fan connector Pin 6 (BU-BK wire) ((fan connector connected)) start the truck and run a jumper wire from Ground to that back probe. That will mimic a 100% duty cycle from the PCM and the fan should turn at its fastest speed if the fan is good?
.
That's the next step to figuring this out
Grounding that wire resulted in a clicking noise from the clutch but no change in speed when warmed up
So it wouldn't matter if the engine is cold or warm
.
When you back probe and ground pin 6 (BU-BK wire) the fan should run at 100% duty cycle
.
You have a bad fan assembly
That's pretty much what I figured, thank you very much for all your help!
Hey, good troubleshooting this circuit on your part
.
You nailed it
.
Just be sure there isn't any corrosion in that wiring connector
Is the engine overheating?
If I'm moving no, if I idol for a minute or two the temps climb up.
check all sensors, fuses, relays, wiring and connectors related to fan cooling
schematics are available on charm.li
I checked fuses and relays with no success. I will start to check the wiring though...
Here's what I found
Fan signal speed 12 volt
(Green/yellow stripe)
Power distribution 14 volt
(Yellow/green stripe)
Fan motor control 0 volt
(White/blue stripe)
Voltage reference 12 volt
(Green/violet stripe)
Ground 0 volts/perfect continuity.
(Black/green stripe)