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2000 Taurus Cooling fan not working

04-22-2006, 10:18 PM
I have a 2000 Taurus with a 3.0 and the cooling fans will not come on. If you get stuck in traffic it will start to over heat.

I have two sensors right near the thermostat. The one closest to the firewall must be the sending unit, because if you unplug it the temp gauge won't work. The other one must be the coolant temp sensor. I take it that must also run the fan, also? I have checked the fan relay fuse. I have also tried swapping the low speed and high speed fan relays.

Anyways, it appears the fans spin freely, and I get a similiar resistance between the windings of both electric motors. The fans do not come on when I turn on the air, so I am suspecting the relays?

I remember when they had the old one wire fan sensor, that you could just take off the plug, and ground the wire out to the block and the fan would take off. You could tell if the problem was the fan sensor on those old systems. But this newer coolant sensor has two wires, so I didn't know how to test for a bad coolant sensor, or fan sensor. Does anybody know how?

Anybody got any other ideas, what I might check?

04-23-2006, 01:58 AM
Test the two wires going to the temp switch and see if one of them has power. If yes, then jump the two wires together and see if the fans come on.

Did you check your coolant level?

04-23-2006, 07:51 AM
Has to be bad temp sensor, fan motors died or a bad fan connection and I don't believe both fan motors would die at the same time verified by them spinning freely not making noise. Somewhere I remember reading a guy was told to take the sensor out and clean it good.

Please, before putting your fingers or hands on or near the fans, disconnect the power because they start up quick and you could be seriously injured, as in, cut to the bone, stich, stich, stich.

Overheating is one of the worst thngs that can happen to your engine and number one cause of blown head gaskets. I understand how we want to fix it ourself and save money, but if you go to a shop and have the problem diagnosed and it costs two hundred bucks to fix it, that's a whole heck of a lot cheaper than fixing a blown head gasket or gasket(s). Gets hot enough and pistons expand and can gall/slap the cylinder walls and serious detonation caused by overheating can cause all sorts of problems. Worst case senario you crack a head or the engine block.

04-27-2006, 01:57 PM
I actually did jump the two wires across, but the fans didn't come on. However, I did not check with my multimeter to see if it had power before I jumped them across.

I also don't think there is anything wrong with the motors.

About the temp sensor. Shouldn't turning on the air conditioner turn one or two fans on? If that is the case, the temp sensor should be bypassed when you turn the air on. Shouldn't it?

I'm in the process of looking for a wiring diagram, and then I can get my multimeter out, and find the problem. I hope.

I'm also thinking of just changing a relay, and the temp sensor. But I don't think that is going to help the fans not working on air conditioning, unless it is the relay.

I have been keeping a eye on the coolant level. Is there a way your supposed to bleed the system? I can't seem to find any bleeder screws anywhere.


04-27-2006, 06:42 PM
Here ya go. Have fun

04-27-2006, 08:42 PM
Thanks for the schematic.

Looking at that, I suspect the PCM.

It looks like, if I apply power to the fan relay, and the fan takes off, it is either the wiring from the PCM to the relay, or the PCM. But knowing what I know now, I suspect the PCM. Because the fans won't take off when you turn on the air either. So I would think by looking at this diagram, if the relays are good, it has to be the pcm, because the air conditioning doesn't make the fans work either, and the common part is the PCM. I wonder how much those cost?

So much for making it simple these days. So I guess this means the cooling, or fan sensor is tied into the PCM. It doesn't appear they show that on this diagram.

It looks like when the PCM power relay closes it energizes the coil on the fan relay, which closes the contacts, on the fan relay, which energizes the fan. So if I energize the fan relay manually and it takes off, it has to be before that, which points to the PCM. Now, if it only showed the wiring including the temp sensor, or fan sensor, and how that ties in with this.

Thanks again for the schematic. I appreciate it. You don't happen to have the cooling Temp sensor, or fan sensor section, do you?

04-28-2006, 02:42 AM
Well, before condeming the PCM, you need to make sure that the inputs to the PCM to activate the cooling fan are such that the fan should activate AND that the outputs to the fan relays from the PCM are not active at the same time. If the inputs to the PCM are not such that a cooling fan activation should be triggered, the PCM should not be condemed initially.


04-28-2006, 02:57 AM
Well, before condeming the PCM, you need to make sure that the inputs to the PCM to activate the cooling fan are such that the fan should activate AND that the outputs to the fan relays from the PCM are not active at the same time. If the inputs to the PCM are not such that a cooling fan activation should be triggered, the PCM should not be condemed initially.


What inputs are we talking about? How does one trigger the pcm via the cooling sensor wires?

If the fans do not come on when the air conditioning is turned on, or when it gets up to temp, and if the fans power up when you energize the fan relays, what other part are we talking about here?

How does one activate the input, or take the place of the Coolant sensor to test the rest of it? And, any ideas on why it would not come on when the air conditioning was turned on?

04-28-2006, 04:31 AM
Powertrain Control Module - You're delving deep into the belley of the beast there folks and seems to me there's a lot of other bases to touch before going there. Things like this sometimes complicated and best to pay a qualified technician to diagnose the problem, then if you want, get the parts and fix it yourself PRONTO. Remember, overheating is the number one cause of blown head gaskets.

04-28-2006, 05:24 AM
Is there anyone who knows how to test the inputs of the pcm? Anybody?

04-29-2006, 12:05 AM
The PCM supplies the ground signal for the cooling fan relays through BJT transistors (PCM pins 28 and 46 it appears from the diagram above). You should be able to perform your checks from the sockets for the relays. Pull the relays and measure the voltage between the relay coil with respect to known ground. Turn the key to "Run" to energize the PCM relay. This should provide battery power to one side of the relay coil at the socket. Now check for battery voltage at the input to the switched side of the relay which is provided from the 40A F109 fuse. You should also be able to verify continuity from the output of the switched side of the relays to the connector at the fan motors. On the low fan wiring, you may have to set your meter to measure resistance to compensate for the fan motor resistor.

If all of these check out, then measure the battery voltage across the relay coil terminals at the relay socket with the A/C turned on. If you do not have battery voltage across either of the relay coil terminals, then you need to verify that the signal into the PCM is appropriate. That determination will come from measuring the resistance or voltage at the A/C switch input to the PCM and the coolant temperature sensor to the PCM. I'm on business travel so I don't have the PCM pinout available to me at this point.

If the inputs to the PCM are correct, indicating the PCM should be providing a ground to the relay, and the PCM is not providing that ground, the PCM is probably the culprit. You'd of course want to verify that there is continuity between the relay socket and the PCM connector at this point.

If all signals to the relay are correct, then the problem would appear to be with the relay, the fan motors, or a high resistance in the supply wiring which limits the current available to the motors, preventing the fan motors from starting up and running.


04-29-2006, 12:58 AM
Shorod, you are the man!!

Hopefully, I won't need the pin numbers for the coolant temp sensor input to the pcm. Or the pin numbers for the pcm input from the AC.

But, just knowing that the PCM controls the ground to the relay coils, and knowing that one should have power on one side of the relay coils is plenty enough information to get started with.

Now looking at the schematic, I see what I believe to be the culprit. The PCM relay in the Battery Junction Box on top of the radiator, controls the positive power, to both the low and high speed relay coils. So if that was out, it would shut down both fans, no matter the signals from the pcm. Fuse 109 the 40 amp does the same, but I already checked that.

I will check the PCM relay as well, making sure I have power to the coil side when the key is on, and giving it a ground to make sure the contacts close, and also making sure it has power on one side of the contact. But you gave me plenty enough information to chew on, and got me headed in the right direction. And because of the time you took, I think I have it under control.

I don't suspect the low and high speed relay, but the pcm relay at this point, so I will start there.

Thanks for taking the time to write that out for me, it looks like it took some time, and it has helped me see the light at the end of the tunnel.

The money I spent on my electromechanical education will give me a little more return. Thanks to you, I now feel confident that I can actually troubleshoot this thing effectively.

I will get back to you on this, and let you know my findings.

04-29-2006, 01:02 AM
By the way, did you use to be a Ford mechanic? How did you learn all of this?

04-29-2006, 10:47 PM
By the way, did you use to be a Ford mechanic? How did you learn all of this?

Well, the PCM relay also provides power to the PCM, so if the car starts and runs, the PCM relay will not be the problem. Sorry.

In 1979 my parents started their own auto repair shop. I was in pre-school at the time and Mom would pick me up from morning pre-school, then I'd spend the rest of the day at the shop shadowing Dad. As I grew older, I began to spend more time tinkering on cars, and even was "employed" by Dad from age 14 until my junior year of college when Dad suggested I find a job more along my major (electrical engineering). So, that's what I did. Now I'm a senior systems engineer by trade and an automotive "tech" by hobby.

Good luck.


04-29-2006, 11:39 PM
Well, when I pulled out the pcm, the car wouldn't start, so I then realized what you already knew. At anyrate, I went through pin by pin, on the relay sockets. I then applied power to the coils, and the contacts closed. I checked the fuse, and finally pulled the fan connectors off, and checked for power. Sure enough there was power to the fans. So I then pulled the fans out and ohmed them out, and there was nothing. I thought I was getting a good contact on them before, but I was going low speed to high speed windings, which was giving me a reading.

Long story short, motors were bad, and both windings were open, on both motors. I even tried to fire them up out of the car, and nothing.

Anyways, if I would of started on that end first, it would of saved me some time. But with the schematic it wasn't to bad. I suppose it only took about 20 minutes of checking things out, to realize there was nothing wrong with the pcm relay, or the other relays, and there was power to the motors.

Thanks again for your help. I learned a lot today on at least one version of the Ford Cooling system.

Just curious, who else besides Ford ties there cooling fans into the PCM?

05-01-2006, 10:13 PM
Just about any modern car now days will have cooling fans controlled by the PCM (although other manufacturers may call it something other the PCM, like ECM or ECU, etc.). With computer control and the strict emissions standards today, it only makes sense to have the fans controlled by the computer. The computer needs to know what the coolant temperature is to properly adjust the air/fuel ratio. The computer needs to know when there is a demand for the A/C compressor to adjust the idle speed. The PCM is also often tied into the alternator to help it determine the proper current to provide the electrical system. With the computer having knowledge of all these loads and fan requests, it seems very reasonable to have it control the cooling fan(s) as well.


03-31-2010, 03:21 PM
Hi, I was wondering if you had a link for that schematic? Also, where did you buy your replacement fans at?

noa brando
11-16-2012, 12:50 PM
on an o1 taurus there is a small black box to the right of your battery toward the bottom. unhook the box remove the cover and replace the relay inside. i had the same exact problem and i figured it out on my own. i replaced that relay started up my car and hey,hey,hey the cooling fan came on turned on the ac and that fan came on as well. finally figured it out.

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