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Fan will not run unless i unplug temperature sensor

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Most likely bad fan relay or wire from it broken or bad connection.

Posted on Mar 28, 2011


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95 firebird the cooling fan wont come on unless I unplug the fan sensor then it comes and cools the car right down

The fan relay is grounded by the computer (ECM) so you need to test that pin on the ECM connector. When you unplug the ECT sensor you send it into default that is why it runs. Please keep in mind that the fan is not activated until the engine reaches 220F-225F that is well passed the middle of the temperature gage scale . Make sure you really have a problem.

Nov 11, 2016 | 1995 Pontiac Firebird

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I have a Chevrolet 2005 Suburban and the heating/cooling fan will not cut off unless I disconnect the battery or take out the fuse, any ideas?

most likely your temperature sensor for the fan is stuck on your heating fan will run when the key is off if it is getting a high temperature signal from the switch ,, put it back together and get the fan to run then unplug and plug back in sensors around the thermostat and water pump areas until it stops, then replace that sensor

Oct 20, 2014 | Chevrolet Suburban 2500 Cars & Trucks

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I have an 89 camaro the cooling fan will not work unless you unplug the temperature sensor or hotwire it. I have replaced the temp. sensor and fan relay. I have tested wires to sensor from the sensor to...


Unplug the coolant temperature sensor while the engine is running. This should cause the fans to turn on low then kick to high, IIRC.
Typically when the engine computer loses the signal from the coolant temp sensor, it just turns both fans on high so the engine will not overheat. Ultimately, the fan is controlled by the computer. When it receives a signal from the temp sensor that reads the appropriate temp, it turns the fan on. One easy option is to wire a switch to the cooling fan relay. Then you can turn it on and off when you need it. I would not recommend running the fan constantly. You will burn out the fan motor and you'll never get up to normal temp for your sensors.

Check for coolant level and bad motor.

However as far as the fans and "disconnecting them from the temp sensor"..... The fans DO NOT connect directly to the temp sensor. They connect to the PCM (computer). The PCM reads the coolant temp sensor, and determines when to turn on the fans. It also uses the coolant temperature to control several other functions, including the transition from "open loop" A/F ratio control to "closed loop" A/F ratio control. It uses the temp to set the idle speed on cold start. It uses the temp to determine the cold start fuel enrichment. If you run this way, your car will be hard to start, it will run excessively rich, wasting fuel, and possibly even damaging the engine by diluting the oil.

Please get back to us if you have further query or else please accept this "particular" solution.

Sep 18, 2011 | 1989 Chevrolet Camaro

1 Answer

My cooling fan does not turn on unless i unplug it from the temperature sensor i have replace that sensor 3 times and it still does not work

Does it come on when the AC is on?
Odd .
Fan won't come on till like 230 degrees.
Or run a small ground wire from the relay to a switch inside.

Jun 17, 2011 | 2001 Pontiac Grand Prix

1 Answer

What causes the fan to keep running on a 2000 volvo s40

The temperature sensor for the fan now does it run when the engine is cold,with the a/c off? That fan only need to reun when the engine is about to exceed operating temperature,The sensor itself may have shorted out, It is not need when engine is cold unless the a/c is commanded on

Apr 22, 2011 | 2000 Volvo S40

2 Answers

My 1995 buick century 4 door v6 3.1 is over

You need to change the "Coolant Temperature Sensor". That usually controls the fan. If the fan does not run, you will overheat.

Jul 28, 2010 | 1995 Buick Century

2 Answers

Coolant temp sensor

NO, the sensor is good.

Apr 25, 2010 | 1997 Ford Taurus

1 Answer

Fan does not run unless the a/c is on

Replace the likely bad engine temperature sensor.

Oct 11, 2009 | 1996 Ford Taurus

1 Answer

Radiator fans won't turn on unless ac is running. why does it do that, how can i fix it?

Radiator fans only need to run when the engine temperature exceeds a predetermined range for the sensor. I would think the AC bypasses the sensor via a separate circuit. The engine temperature would raise if for example the ambient temperature increases on a hot day or if you were clinmbing hills about the mountains, or if the radiator water level was low etc.

Hope this helps somewhat.

Sep 14, 2008 | Mitsubishi Lancer Cars & Trucks

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