Mechanics

FAN IS ALWAYS ON

1992 Pontiac Sunbird

Other Category problem
1992 Pontiac Sunbird 6 cyl Two Wheel Drive Automatic 225000 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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Lmack65
January 9, 2008.




DOES THE VEHICLE HAVE AC?

Tiny
Mastertechtim
Jan 9, 2008.
No AC

Tiny
Lmack65
Jan 9, 2008.
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.

Tiny
Mastertechtim
Jan 9, 2008.
Thank You I appreciate anything you can do for me.

Tiny
Lmack65
Jan 9, 2008.
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.

Tiny
Mastertechtim
Jan 9, 2008.
I wil try that thanks

Tiny
Lmack65
Jan 9, 2008.
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

Tiny
Lmack65
Jan 9, 2008.
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.

Tiny
Mastertechtim
Jan 9, 2008.
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.

Tiny
Lmack65
Jan 9, 2008.
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.
AD

Tiny
Mastertechtim
Jan 9, 2008.

AD