Since I've had this car, the fan has never worked properly. It will come on only when the A/C is on. I got under the car to see if I could find a problem with the cooling fan sensor right above the starter, and yeah, I found one. The plastic plug had broken off and was dangling, not hooked up to anything. I replaced the plug, but it still wouldn't come on no matter what the engine temperature is. So I replaced the sensor, and still nothing. This afternoon I disconnected the relay and hooked up one that I know works for sure, and it still would not come on even though the temp gauge was reading maybe a little more than 230 or 235.

I turned off the car, put the old relay back on, and closed the hood. As I was picking up some tools, I hear a noise. I open the hood, and the fan is on (came on after about 45 seconds after shutting off). Ok, I turn on the car, and it turns off. I waited again for the temp to rise a bit, but the fan wouldn't come back on. This time I turned the car off and the fan wouldn't come on.

I spent some time looking at the wiring diagram in the Chilton's manual, and I can't see why it would come on after turning off the car. Also, aside from hooking up a test light to the wire going to the sensor to check for current, what else can I do to find my problem? I don't understand this at all.

 

The thing right above and forward of the starter is the knock sensor. Depending on the year of your car the fan is run from the ECM via a sensor in the front of the intake manifold. If it is a later year it might be run from a switch screwed into the passenger side head.

 

so you have one electric fan. that probably runs off the the ecm.
the ecm for my car at least (i have factory dual fan setup) reads the temp from the temp sensor on the front of the block and once it reads like 227 the ecm turns the fan on..


the only way i would see the fan come in is that the relay is funking or their is some kinda of shorting together of the always hot wire (orange) and a ground...

 

Morley, you are correct. The knock sensor is mounted right by the starter on the block. I wasn't sure if the coolant fan sensor was threaded into the head or the block, so I just mentioned it was by the starter. I went to go take a look, and its in the passenger side head, like you said.

MDFormula350, I looked through the wiring diagrams and for my car the ECM isn't anywhere in the diagram. The sensor that is mounted in front of the block is the coolant temperature sensor. I ran winaldl on the car once before, and that sensor is working, but it is not connected to the cooling fan in anyway that I can see. If the ECM did control when the cooling fan comes on, I can see that happening, but I don't think it does. The diagram shows a switch mounted on the a/c compressor, the a/c control panel, and the coolant fan sensor in the circuitry to start the cooling fan. The weird thing is that the fan started on its own after turning off the car. It has never done that whether or not the car was running. And to make things more unusual, everything is exactly as it has always been. All I did was try a different relay, and when that didn't solve the problem, I put the old one back on.

Does any of this make sense to anyone?

 

yeah makes sense i am just use to dual fan setups.
maybe someone else can help.
i found a diagram though.

 

WTF? I was looking the wiring diagram again and it mentioned that the coolant fan switch is closed above 238 degrees, and open below 214. Isn't that borderline on being hot enough to damage something, or atleast blow a head gasket?

I haven't let it get passed that temp, so if that is correct, I have never given it a chance to see if its working or not. I think the hottest its been is 230 or 235.

 

Try grounding the wire to the fan switch with the key on. That will tell you if the circuit is good or not.

 

I'm gonna try that as soon as I get a chance. Regardless of whether or not the sensor is the problem, I think I am going to replace it with one that'll let the fan turn on at a lower temp, somehwere around 200 degrees or so. I'm not too comfortable with letting the car get up into 240 degrees. If the sensor wasn't the problem, then whenever I figure it out, atleast I don't have to worry about the engine getting so hot.