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1992 Pontiac Sunbird Fan is always on

Tiny
LMACK65
  • MEMBER
  • 1992 PONTIAC SUNBIRD
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 225,000 MILES
The problem I have is that the fan is always on. As soon as I start the engine it is on and never stops untill I shut the engine off. I have taken it to a mechanic and have had it looked at. He hooked it up to his computer and found that the coolant sensor was reading -39 degrees even when the engine has been running for a long time. He looked at my coolant sensor and said it was working, he also traced back the wiring and found it was all good all the way to the computer. So I replaced the computer and the problem is still there. I replaced the coolant sensor relay with a new one and still the fan stays on. I have the smell of gas as well, he told me that since the computer thinks the engine is at -39 degrees that the choke stays open and therefore uses more gas thus the smell. The thing I dont understand is why would the fan be on in the first place if the engine thinks its -39 degrees?
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Wednesday, January 9th, 2008 AT 2:41 PM

19 Replies

Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
DOES THE VEHICLE HAVE AC?
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Wednesday, January 9th, 2008 AT 2:49 PM
Tiny
LMACK65
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  • 14 POSTS
No AC
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Wednesday, January 9th, 2008 AT 2:51 PM
Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
Im going on all data to check wiring diagrams, so we can get to the bottom of this. Ill be back as soon as I can. Hang in there.
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Wednesday, January 9th, 2008 AT 3:00 PM
Tiny
LMACK65
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Thank You I appreciate anything you can do for me.
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Wednesday, January 9th, 2008 AT 3:04 PM
Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
Ok heres where it gets tricky. Im assuming your vehicle came from the factory with no ac. If your computer reads neg 39 there is a problem in cooling temp sensor circuit. You need to check voltage at the yellow wire at the cooling temp sensor. Key on engine off there should be 5 volts.
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Wednesday, January 9th, 2008 AT 3:08 PM
Tiny
LMACK65
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  • 14 POSTS
I wil try that thanks
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Wednesday, January 9th, 2008 AT 3:21 PM
Tiny
LMACK65
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  • 14 POSTS
I have used an old ohms meter and im not sure what setting I should use, but the yellow wire, there is power going to it. About 10 ohms if that means anything. Thanks
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Wednesday, January 9th, 2008 AT 5:16 PM
Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
You need to put it on dc volts. ****I forget, have you replaced the sensor already? **Use your ohm meter and check the resistance of the coolant temp sensor. I have the schematic at work. I think a low ohm reading indicates high coolant temp. If you have an open in the coolant temp sensor, your ohm meter will not read anything. Than your problem would be a bad coolant temp sensor. ** The reason the low temperature would turn the fan on is because the computer knows neg 39 degrees is an error so it goes into failsafe and turns the fan on. **Also use your ohm meter from battery neg terminal to the black wire at the plug, you should have 0 - 5 ohms resistance. If ohms is higher than 5 ohms than you have a bad ground on the black wire.
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Wednesday, January 9th, 2008 AT 5:34 PM
Tiny
LMACK65
  • MEMBER
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Ok I set my omhs meter to DCV 5 and got a reading of 3.5 on the yellow wire I also set the ohms meter to RX1, RX10 and RX1K and they all read 10 ohms on the brown wire. No I havent changed my cooling sensor as my mechanic said it was ok, but I do have another one and if you think I should replace it I will. The only question about that is will I get antifreeze coming out of that hole when I take the old one out.
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Wednesday, January 9th, 2008 AT 5:47 PM
Tiny
MASTERTECHTIM
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Id install the new one onto the harness with the old one still in vehicle. This will tell the ecm a temp of 60 degrees. See if the fan stops running with the new sensor plugged in to harness.
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Wednesday, January 9th, 2008 AT 5:51 PM
Tiny
LMACK65
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  • 14 POSTS
Ok I put the new one into the harness and started it up. The fan is still on though.
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Wednesday, January 9th, 2008 AT 5:57 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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You said the brown wire had 10 ohms it should be less than 5 ohms. Id hook a test light to 12 v and check brown wire, the test light should light. Technically if your ecm coolant temp is really neg 39 and your guy who scanned it did not make a mistake, and you said you had 3-5 volts on the yellow wire, which tells us the integrity of the wiring from the ecm to sensor is ok. Id double check the ground with the test light. If all that tests out ok. The green wire with white stripe on it from the ecm to the fan relay is shorted to ground somewhere. **You said the vehicle came from the factory without ac. Correct. But your vehicle is still wired for ac. So id check harness for a plug that might be chafed somewhere. Because the ac high pressure switch also will turn on the fan
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Wednesday, January 9th, 2008 AT 6:07 PM
Tiny
LMACK65
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Hello again, I am looking at the green wire with white stripe that goes to the fan relay and in the little box it goes in is very gunky and dirty, could that be the problem and can I replace that part if it is?
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Friday, January 11th, 2008 AT 3:46 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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Id cut the green and white wire at a spot that is easy to put back together. Then lets see if the fan turns off.
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Friday, January 11th, 2008 AT 3:50 PM
Tiny
LMACK65
  • MEMBER
  • 14 POSTS
Ok cut the green and white wire, the fan no longer runs, is that a good thing?
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Friday, January 11th, 2008 AT 4:00 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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Ok heres what we do. You said you put in a new ecm. If you can access the green white wire at the ecm. Cut the wire there, then reconnect the other end that you just cut. Turn key on, if fan comes on the green white wire is shorted to ground somewhere, if the fan still is off than there is something triggering ecm to turn on fan. Were almost there!
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Friday, January 11th, 2008 AT 4:05 PM
Tiny
LMACK65
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I have no idea which green and white wire to cut at the ecm, I have 3 separate plugins that have many wires attached to each one?
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Friday, January 11th, 2008 AT 4:44 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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Well heres what we have. We can go on tracing wires that input and output the ecm which could take a real long time for us to find on line. What you can do to save alot of time and aggravation. This repair will cost you about $20 and take you about an hour to do. Go to parts store and get a cooling fan switch for a 1994 camaro with a 5.0l engine. Usually in the help section of parts store you will find the direct plug in plug for this sensor. There are numerous spots to install this sensor in the head, manifold or the engine block where coolant is. Install the camaro coolant fan switch and plug, now run a wire from the green and white at the relay to the switch you just installed. This is your best bet to fix this car. Make sure you get the cooling fan switch not the coolant sensor for the ecm. The cooling fan switch will have only 1 terminal in it. Your cooling fan will now come on at 228 degrees and shut off at about 200. Exactly like the fan should.
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Friday, January 11th, 2008 AT 5:08 PM
Tiny
LMACK65
  • MEMBER
  • 14 POSTS
Hello, me again. I got your last message saying I should get a cooling fan switch for a 1994 camaro. The question I have is, I dont think that will solve the underlining problem of my computer saying my coolant is -39 degrees, and that my choke is always on because of that and that I have the strong smell of gas?
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Sunday, January 20th, 2008 AT 5:35 PM

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