Fan motor

My fan wont start in my 93 taurus 3.8 l. I`ve changed the temp. sensor but it still wont work. If you unplug the sensor and run a connection from the plug to the battery the fan cuts in. as soon as you plug it back in the fan shuts off.

Welcome to the forum!

I assume you are referring to the radiator cooling fan rather than the blower motor for the cabin. On your 1993, the radiator fan is controlled by the Constant Control Relay Module (CCRM). The fan would typically be activated by turning on the A/C or the defroster. If the air temp in your area is above freezing, try turning on the A/C or defrost and see if the fan runs.

If not, I'd suggest that you perform a search on this Taurus forum for "CCRM" since the links to the schematic diagram and pinout for the 1993 Taurus CCRM have been posted before.

-Rod

Do you know if your car received the radiator fan recall repair? This was done to prevent the fan from overheating and catch on fire when it would seize. Ford would install an overload protection fuse. Possibly you have this fuse blown. Unfortunately, I never bothered to have it put on mine, so I don't know exactly where it is, but I would first assume it would be near the fan added to the fan wiring harness. I'd expect it to look like a short section of wire and fuse stuck in at an original connector. Like Rod suggested, the relay may be bad, but I'd check for continuity from it to the fan if that is where the fuse may be. I'm curious to know what you find.

Just changed the relay and checked the fuse ...same results, the fan will only start when you ground the wire running into the temp sensor. Could the problem be the ECA?

Maybe. Which of the two sensors are you taking the wire to ground? Which did you replace? I assume the two wire engine coolant temp sensor for both. It sounds like the sensor you are grounding its wire is bad or not getting grounded at the ECS. I don't believe it is grounded at the engine like the temp sender through its body to the intake manifold. Which terminal/wire are you grounding? One side should measure 5 volts at the black/white wire. I would expect to spark and not get the fan to work. The lt green/yellow has the signal back to the ECA. The dash temp sending unit has a single hot wire that is red/white. To test it, you short the single red/white wire to ground which would give you a gauge reading just as if the coolant was hot. This makes what you are doing and getting interesting. I would want to rule out that the temp units are ok which can be done with resistance testing. I would have thought you would have gotten codes for something if the ECT or ECA were not right.

Wiring harness disconnected, eng off, start with cold engine.
The temp sending unit:
74 ohms cold
9.7 ohms hot

The ECT sensor;
40,5000 ohms cold(65 degF)
3800 ohms hot(180 degF)
to
1840 ohms hot(220 deg F)
(I want bet the farm on the ect numbers I got you, but they should be close. Rod or Autozone.com may have them to confirm)

Basicaly the hotter it is the less ohms you should measure. Less ohms is like having the electric loop completed, like when you were grounding the wire, but I would be 100% sure it is not the ect sensor and the wiring invovled before it is the ECA. Again, shouldn't the eca throw codes? Unfortunately, the resources I have do not allow me inside the ECA to know if it simply is ground for that one wire or what.

It`s the coolent temp. sensor on the top drivers side that has been changed (5 times in the 2 years that I`ve had the car). The fan starts when I ground the green wire. I`ll test the temp sending unit and check the readings I get. It has been scoped 2 times and no codes have come up. Thanks for the numbers.

I don't have the wiring diagram in front of me, but is sounds like the fan, CCRM, and PCM are doing what they are supposed to do. I would guess that either there's a bad connection or wire between the coolant temp sensor and the PCM (corrosion, loose) or a bad coolant temperature sensor.

Keep in mind that, as mentioned above, there are two coolant measuring devices, one that control the guage and only the guage and one that provides feedback to the PCM. Since grounding the green wire makes the fans turn on, you are probably on the right sensor. Are you sure this is the sensor that was replaced?

Tonight I'll try to take a look at the wiring diagram to see if I can come up with more ideas.

-Rod

I`ve replaced both sensors with the same results. When I first started the car I unplugged the temp. sensor and the fan cut in like it should when unplugged but after reattaching it the fan would not come on again even after letting it get to a hot running temp. or unplugging again.

Does the fan come on when the A/C or Defrost is turned on? Are you sure the engine is getting hot enough to warrant the fan coming on? What range are you seeing on the temp guage? Do you have an IR thermometer than can give you an indication of the head thermostat housing temperature?

-Rod

Tried turning the AC on but fan still wont cut in. I let it warm up til it was well over half on the temp gauge. I`ll check into the thermometor.

It would be interesting to take a voltage reading across the two terminals of the ECT sensor, then across the LG/R wire of the ECT sensor and battery terminal ground. How do the readings compare? Similarly, measure across pin 7 at the PCM (LG/R wire) and battery ground. How does that compare to the voltage reading across the ECT sensor?

-Rod

I found a table in my Mitchell PDA module that corresponds pretty closely to the numbers tripledaddy posted earlier. Another test you could try would be to substitute a potentiometer (variable resistor) for the ECT for testing purposes. Find a 50k linear potentiometer and tie the two outer-most terminals to the two leads for the ECT. Slowly turn the potentiometer until the cooling fan kicks on. At that point, measure and record the resistance across the two terminals of the potentiometer. Reinstall and turn the potentiometer the other direction until the fans shut off. Remove, measure and record the resistance.

See how the numbers you recorded correspond to the following table:
Temp Voltage Resistance
50 F 3.51V 58,750 ohms
68 3.07 27,300
86 2.60 24,270
104 2.13 16,150
122 1.70 10,970
176 0.78 3,840
194 0.60 2,800
212 0.46 2070

-Rod

That's way over my head. I will see if I can find somebody to help with that one. Thanks for the numbers.

Tell me if this might have been the problem,the new temp.sensor that I installed was plastic, so I went and bought a brass one for twice the cost and the fan started working after the car heated up. I cant see it being that simple.

The quality of part you installed certainly could be an issue, and the fix may have been that simple. The brass should stand up to the constant heat quite a bit better than the plastic, and the quality of the materials will help indicate the quality of the part. Were the 5 other ECTs you installed also plastic?

-Rod

It could be that simple, since I assume you haven't measured the sensor to see if it was any good, since you said nothing about that either way. I think we were going on the basis that you had established it was in fact good and Rod looked in other places that could cause your problem.

Where did you buy and what brand were the plastic and brass ECTs? Were you ever able to measure the ECT values when cold and hot? I would have thought it should have revealed the same conclusion it wasn't working right, but hopeless "I want to know thats" like me want to learn from your experience rather than just assume your plastice ECT was junk or something more to it to broaden my knowledge. So, if you did measure the ECT values, I'd like to know what you found. Sometimes being separated from the car by two computers and translational differences, makes it hard to diagnose some things that from afar seem involved but up close with our hands on it ourselves can turn out to be as simple as what you have found. So much for virtual mechanics. Do you think you can work on that Rod?

So much for virtual mechanics. Do you think you can work on that Rod?

That may not be so far off. There are a few forums that have video archives. One or two really dedicated members take video of various repairs they make, such as how to replace the brakes, how to replace the cabin air filter, how to rotate the tires, etc. They then post the video clips to youtube or similar and post the links on the forum in the "Help" section of the forum. A video of "How to your use multimeter to take measurements" and "How to backprobe a connector" would be easily adapted to multiple areas.

-Rod

The brass one was "Standard" and the plastic ones were "Kem" and one other brand that I cant recall. All of the sensors that i had used up untill this one were plastic.

Hopefully this brass one will be the fix and you won't continue to fight this problem for a few years from now.

-Rod