94 GT electric fan problem

KXT · Apr 13, 2010

Car = 94 GT, farely stock.

I received the car with blown headgasket and don't remember if the fan was working before I traded engines. Now at least with the new engine the fan does not work.

Here's what I know so far. Car on the fan does not come on even if engine temps are HOT. Engine temp sensors has been tested (good) and changed with another just in case (also tested good).

When engine is on, if the engine temp sensor is removed the fan comes on.

During the ECU self test KOEO the high and low speed fans will come on as they are supposed too during the test.

The fan systems consists of fan, engine temp sensor, ECU, and CCRM (relay). I cannot figure out why the ECU is not turning on the fans when it gets hot.

I know how change the wiring (ground 17/14) and turn it on with a switch but I really want to figure this problem out and not change from the factory wiring.
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toyman · Apr 13, 2010

My Ford service manual says the fan doesn't come on until 220*F (low fan) and 230* (high). The fan should come on high with the A/C running while at idle.

KXT · Apr 14, 2010

Thanks for posting the numbers but the fan never cuts on regardless of temp. Also the A/C has been removed... anything with A/C removal can cause the fan not to come on?

desertcox05 · Apr 14, 2010

To test the circuitry, when you pull codes one of the first things you'll hear is the fan kick on low for a couple of seconds then hi for a couple seconds.

KXT · Apr 14, 2010

as said in the original post the fan does come on high and low during the ECU self test. Therefore I would think the CCRM and ECU output are fine. This leads me to the temp sensor input but it seems good too.

KXT · Apr 14, 2010

desertcox05 · Apr 14, 2010

have you read the temp with a real guage. our guages are known for not being very accurate.

fyassine · Apr 14, 2010

I am sure a few more knowledgeable folks will chime in, but in my case the two wires going to the ECT were barely hanging on by a couple strands of wire.

With that said, my advice would be to check the length of the cable going to that sensor for just that. I am sure the next steps will involve breaking out a multimeter or manually wiring the fan until you can figure out the real cause of the problem.

99FiveOh · Apr 14, 2010

One thing I get tired of hearing, and no offense to anyone, is that our gauges are inaccurate. Last time I checked there wasn't ANY numbers on the gauge. Nowhere on it does it say "THIS IS WHAT YOUR TEMP IS" It is a guide to let you know if there is a problem. If you get into the red zone you have a problem! The fan should be on full blast if you go past the mid point on that gauge period. It would seem that if it did indeed come on before at a specific point in the temp. gauge's sweep, then the gauge is functioning properly and it's the fan circuit that is a fault.

This sounds exactly like a faulty ECT signal to me. You just have to figure out if it's bad or the wiring is bad. Also maybe you should pull it out and see if the hole is all gummed up. If that sensor doesn't see the high temps, the EEC will never know it's hot enough to engage the fans.

Chythar · Apr 14, 2010

I agree with Mark here. If the computer isn't reading the right temperature, it's going to put more fuel into the engine to warm it up, and it will never turn on the fan. KXT, you'll need a good code reader that can read engine sensor data (called PIDs, I believe). You'll be able to see what the computer thinks the engine temperature is.

Be aware that there are TWO temp sensors on our cars: the ECT (passenger side, screwed into the black heater tube) and the CTS (driver's side by the distributor, screwed into the lower intake manifold). The ECT feeds the computer, and the CTS feeds the gauge in the dash. The computer has no knowledge of the CTS at all. The code reader is necessary to tell you which one is the problem. You could have a wiring issue that alters the values returned by the ECT and CTS, so keep that in mind.

To give you an example, my stock temp gauge on my GT reads high. It gets up to the "M" on the gauge before the fan turns on. However, my code reader says engine temps are 220* when the fan turns on, so I know that either the gauge is off or the CTS is bad.

shoua50 · Apr 19, 2010

sounds like a bad ground for the fan or relay. they may run during the self test, but that only cycles it for a short second at low amperage.

MADMAC94 · Jun 19, 2010

I have seen this issue over and over again in research. I haven't seen anyone post their resolution, outside of installing aftermarket fan relay kit. I too have narrowed it down from sensor to ECM. Fan kicks on both high and low speeds during KOEO test proceedure. My fan will run on high, A/C on, and when it reaches 230 but not on low. The CCRM is new and all sensors are new. I jumped the ECT plug with a 2k resistor and the fan runs on high.

Then other issues are at higher temps, have noticed all gages but RPM fluctuates. I have check all my grounds and found no problems. I am going to ripp into it today and fix this one way or another.

MADMAC94 · Jun 20, 2010

Just wanted to drop back in to let ya know that I fixed some of the problem. I fired up the Fluke and found high resistance between the engine and frame rechecking my grounds with a good meter. I went through and reworked all my grounds and connections. I used electrolitic grease on all the connections. The stock water temp gauge is within normal standards ( if that is what you could call it?) and all other gauges are stable. The radiator fan is coming on sooner and keeping it cool. I still have to locate problem with low speed fan not running?????

94 GT electric fan problem

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