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Old 04-09-2011, 12:46 PM   #1
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radiator fan always running

I have a 1986 Z28 305 TPI. The cooling fan is always on even at engine startup with engine cold. When I disconnect the wire bundle to the relay up at the passenger front of the engine by the radiator this disables the fan. I have also tried changing that relay but get the same result so the problem must be other than the relay. I am thinking a sensor but I do not know which temp sensor controls the cooling fan, or if it is something else. Any help appreciated.
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Old 04-09-2011, 08:19 PM   #2
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Re: radiator fan always running

The ECM controls the fan, based on the coolant temp sensor input. But there are some trouble codes that cause the fan to run all the time. Have you scanned it for codes?
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Old 04-13-2011, 11:42 AM   #3
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Re: radiator fan always running

I did recently scan it for codes, and even though the check engine light is on, the machine stated to the effect "scanning ok, no codes at this time...." So that unfortunately did not give me any leads. That of course is another problem, what would cause a poor code result like that?
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Old 04-14-2011, 05:27 PM   #4
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Re: radiator fan always running

Quote:
Originally Posted by Stealth_Z28 View Post
I did recently scan it for codes, and even though the check engine light is on, the machine stated to the effect "scanning ok, no codes at this time...." So that unfortunately did not give me any leads. That of course is another problem, what would cause a poor code result like that?
You don't need a "machine" to scan your ECM. You can flash the codes on the SES light by shorting two pins in the ALDL connector with a paper clip.

This is for a 93, but your should be similar:

http://shbox.com/1/dlc2.jpg
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Old 04-16-2011, 12:08 PM   #5
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Re: radiator fan always running

The paper clip worked, so much for the $200 machine I borrowed at Oreilly's. Anyways, I got codes 14 and 42. What problems could be causing this and what do they mean?
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Old 04-16-2011, 02:43 PM   #6
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Re: radiator fan always running

DTC 14 = Faulty coolant temp sensor.

DTC 42 = I believe the spark module in the distributor.
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Old 04-17-2011, 08:47 PM   #7
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Re: radiator fan always running

Well, the sensor that gives the gauge a reading seems to be ok as I have changed that recently and the gauge reads. There appear to be two other sensors just above the water pump slightly to the passenger side. I have actually already changed one of those sensors, the one to the right. Now I understand there could still be a wiring problem if that is the fan sensor. Do you know which of those two sensors controls what specifically?

I'll also mention that my temp. gauge used to not work only for the reason that on ignition start up, that needle would pop way to the far right of the gauge and actually get stuck up there. I fixed that by putting a small rubber "bumper" there for it to hit and bounce back. I don't know if that was normal for it to go forward like that but nonetheless that is how I fixed that problem after literally years the temp gauge "not working."
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Old 04-17-2011, 09:41 PM   #8
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Re: radiator fan always running

I don't know the details of the 305. Typically, the gauge runs off a single wire sensor, and the ECM gets data from a 2-wire sensor. According to Chiltons, the wires are yellow and black for the 2-wire sensor that connects to the ECM.
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Old 04-19-2011, 02:44 PM   #9
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Re: radiator fan always running

Just what sort of test do I do with the wires to determine if there is a fault? As I mentioned, I did also change one of these sensors so I believe at least the one sensor should be good, if it wasn't already since that did not fix the problem.
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Old 04-19-2011, 02:50 PM   #10
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Re: radiator fan always running

p.s.
I found the link below for all codes. I am going to ignore code 42 for now as that may have been caused to to the 1/2 engine not firing from the faulty fuel injector fuse.
http://www.iroczone.com/2009/10/1982...maro-firebird/
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Old 04-19-2011, 04:40 PM   #11
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Re: radiator fan always running

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Originally Posted by Stealth_Z28 View Post
Just what sort of test do I do with the wires to determine if there is a fault? As I mentioned, I did also change one of these sensors so I believe at least the one sensor should be good, if it wasn't already since that did not fix the problem.
Key on, connector off the sensor, you should have 5V. To test the sensor:

http://shbox.com/1/4th_gen_tech2.html#ect

That's for a 95, but the resistance readings will be the same.
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Old 04-20-2011, 01:34 AM   #12
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Re: radiator fan always running

I haven't had a chance to perform that wire test, but we did do an experiment, that is disconnected another sensor (4 terminal just below the TSP) which appears to plug into the plenum or intake manifold located at the front passenger side. Do you know what this sensor is called/controls? The factory numbers on it are :80406 a3405. When the plug for this was disconnected the fan did not run, but also the engine would stall if idle was attempted so the gas pedal needed acceleration to prevent engine stall. I don't know if the mere disconnection only cut off power to the fan, or if there is a more controlling aspect related to fan operation. Your year may not have this sensor so you may have no idea what I am referring to.

(Within that link you posted it states:
"Fans will also come on when the SES lamp comes on. The PCM does this when certain (most) DTCs are detected to protect the engine from a situation where it may overheat.

I am thinking I will clear the codes and see if the PCM keeps running the fan or not. I will add however, that my continuous fan problem existed before my fuel injector problem so I am doubtful that would fix the problem.)
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Old 04-20-2011, 05:30 AM   #13
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Re: radiator fan always running

By TSP do you mean throttle position sensor (TPS)? The idle air control motor has 4 wires and would be near that. That's not a "sensor".... its an actuator - a little stepper motor that moves a pintle to control the air flow, to control the idle RPM. Wires are light green/black, light green/white, light blue/black and light blue/white.
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Old 04-20-2011, 01:05 PM   #14
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Re: radiator fan always running

Yes, I meant the TPS. From what you described, that sounds like the idle air control motor that was disconnected for the experiment. Evidently, there is some relationship with that to power (or more) going to the radiator fan. I will check the fan temp sensor voltage and clear the codes later today and post the results.
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Old 04-20-2011, 11:46 PM   #15
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Re: radiator fan always running

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Originally Posted by Knucklehead27 View Post
whats up guys. i'm new to the forum but not to F-bodies. I have an issue with my 86 IROC that is along the same lines as this topic. when the car is moving its temp is fine. but when i get stuck in stop and go traffic it begins to over heat. i have noticed the cooling fan does not come on til the car reaches about 255*F. i bought a new sensor for the ECM but i'm having trouble locating it. would anyone happen to know where i could look? thanks in advance.
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