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No volts to cooling fan

Tiny
NONMIANNOIARE23
  • MEMBER
  • CHEVROLET CAVALIER
I have a 1991 Chevy Cavaliel with approx 117,000 miles 2.2L, automatic. I am having a problem getting the cooling fan to work. The fan will not come on at all, not even if you turn the A/C on. I have replaced the thermostat, temp sensor, Temperature Switch, and even tried a new relay if there is only one. The only way the fan comes on is if you hardwire the fan to the battery or if you unplug the Temp sensor which causes a trouble code to default the fan to come on.

If you can help me fix it I will make a donation. I am NOT getting 12 volts at the fan, I am getting 12.4 V at the fusible link and at the relay but nothing coming out of the relay to the fan, I get 12.04 V at the temp switch but for some reason I only get 5.03 V at the coolant temp sensor. I followed the two wires for the temp sensor all the way to the big connector with all the wires that go into the inside of the car by the back firewall and I am only getting 5.03V at the temp sensor wire there as well, If you give me the answer that allows me to fix this problem I will make a donation.
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Tuesday, October 23rd, 2007 AT 7:07 PM

19 Replies

Tiny
RASMATAZ
  • MECHANIC
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The computer is the one that energizes the fan relay by getting a signal from the coolant temperature sensor

Did you test the CTS resistances hot and cold test. I suggest you check it otherwise the computer is not gonna pick the correct signal from it and it'll refuse to energize the fan relay

Your 5.3 volts at the CTS is okay what about the black wire to ground do you have continuity to ground if not you have an open on it to the computer pin out no. B-12
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Tuesday, October 23rd, 2007 AT 7:41 PM
Tiny
NONMIANNOIARE23
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I am new to using the digital multimeter, how would I do the tests you suggested.
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Tuesday, October 23rd, 2007 AT 9:23 PM
Tiny
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1. Put meter on ohm scale @ 20K

Disconnect CTS connector

2. Put red lead on the voltage input to the CTS terminal

3. Black lead to black wire which is ground.

Remember the colder the CTS the higher ohms/resistances. and Vice versus.

Read the sensor before you start the vehicle, then when it gets up to normal operating temperature read it for hot readings. Compare readings w/chart

When you test if for cold and it doesn't give any reading the sensor is bad.

See below chart for your CTS


https://www.2carpros.com/forum/automotive_pictures/12900_1991_cavalier_CTS_values_1.jpg


www. .com
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Tuesday, October 23rd, 2007 AT 9:49 PM
Tiny
NONMIANNOIARE23
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I will try it but I do not think it is the sensor since it was doing this with the old sensor that was in there and it is still happening with the new sensor that I put in.
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Wednesday, October 24th, 2007 AT 4:15 PM
Tiny
RASMATAZ
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Check the wires for the CTS could be shorted or open going to the computer.

Next step to troubleshoot is from the computer to the fan relay.
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Wednesday, October 24th, 2007 AT 5:02 PM
Tiny
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If I understood you correctly, I removed the cts connector and I placed the read meter lead to the connector on the hot side and I took the black lead and touched it to the ground side of the cts connector. At first the meter read 1 then when I did above I got a reading of 4.53 when absolute cold, I tried to take a reading when the car was running and the meter stayed at 1. I shut the car off and I tried it again and got a reading of 4.05 which is no were near the numbers in the chart so I do not know if I did it right
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Wednesday, October 24th, 2007 AT 5:04 PM
Tiny
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Disconnect the connector on the CTS then read the sensor.
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Wednesday, October 24th, 2007 AT 8:28 PM
Tiny
NONMIANNOIARE23
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When the car was completely cold and not running I completed the sensor with the leads of the meter and the first reading I got was 3.9. Then when I started the car and checked it I got a reading of 2.8, then over the next 20 minutes or so it started dropping.1 until it got down to.17 then I shut the car off because the engine felt very hot but the temp gauge only read a little more than half.
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Friday, October 26th, 2007 AT 3:12 PM
Tiny
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What scale on the ohmmeter are you using? Base yourself on the chart. Looks to me its out of range.

If it bothers you, you can use another source of swicth power to operate the fan without the computer/relay.
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Friday, October 26th, 2007 AT 4:03 PM
Tiny
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I was using the one that you told me to use the 20K
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Friday, October 26th, 2007 AT 4:43 PM
Tiny
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3.9 is equal only to 3,900 ohms on the 20K scale. You should have more than when the CTS is cold. Then it will start dropping as it heats up.

What's your local temperature?
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Friday, October 26th, 2007 AT 8:01 PM
Tiny
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When I did the test it probably was about 50-60 degress today. Just to make sure I am doing things right I added some pics. What you are looking at is the digital meter at 20K, the other pic is the cts which I cut the 2 wires and stripped them so I could take a reading easier instead of trying to get the leads inside the sensor.


https://www.2carpros.com/forum/automotive_pictures/107636_40600001_1.jpg



https://www.2carpros.com/forum/automotive_pictures/107636_40600003_1.jpg



https://www.2carpros.com/forum/automotive_pictures/107636_40600005_1.jpg

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Saturday, October 27th, 2007 AT 12:24 AM
Tiny
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What is the reading? I cannot see it the window is not showing.
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Saturday, October 27th, 2007 AT 3:58 AM
Tiny
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That is how I got the readings earlier, the cold reading of 3.9 and then the dropping reading after that.
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Saturday, October 27th, 2007 AT 2:05 PM
Tiny
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You need to test for continuity between the relay and PCM.
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Saturday, October 27th, 2007 AT 4:49 PM
Tiny
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I do that the same way with the 20K setting? I have volts up to relay
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Saturday, October 27th, 2007 AT 10:41 PM
Tiny
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At the relay what color is that wire that has 12v

Also did you check the coil and switch of the relay?
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Sunday, October 28th, 2007 AT 1:50 AM
Tiny
NONMIANNOIARE23
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At the relay it is the red wire that comes from the fusible link that has the 12 volts. Coil and switch?
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Sunday, October 28th, 2007 AT 2:11 PM
Tiny
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What would be the best way to hotwire the fan? I ran a rocker switch from the inside of the car with 18 gauge wire. I ran 3 wires, one from the power supply off the fusible link that use to run the fan, one to power the hot wire for the fan, and the last one I grounded to a bolt and stud on the body but when I connected the battery the fusible link started to smoke. What did I do wrong?
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Friday, November 2nd, 2007 AT 7:10 PM

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