Question about 1993 Pontiac Grand Am

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My 93 pontiac grand am cooling fan won't turn on when the temperature reaches 220 degrees but if you unplug the coolant sensor the fan runs all the time, I've checked the relay and it is working fine what else could cause the problem and is the a/c compressor hooked up to the same circuit because now the a/c compressor doesn't turn on?

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If the fans run when the sensor is unplugged there is nothing wrong with the relays. The computer automatically runs the fans when it recorded no info from the sensor to avoid overheating. The temp sensor is faulty. The ac compressor is not on the same circuit, it is not running because the sensor is unplugged and the computer is not able to determine coolant temp and disables the ac to avoid overheating.

Posted on Mar 11, 2011


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Hi there:
The engine coolant temperature sensor is a variable resistor with a range of -40 degrees F-265 degrees F (-5 degrees C-129 degrees C).

The engine coolant temperature sensor provides an input voltage to the PCM. As the coolant temperature varies, the sensor resistance changes resulting in a different input voltage to the PCM.

When the engine is cold, the PCM will demand slightly richer air/fuel mixtures and higher idle speeds until normal operating temperatures are reached.

The engine coolant temperature sensor is also utilized for control of the cooling fan.


Fig. 1: Engine coolant temperature sensor location - 3.3L and 3.8L engines

Check this test procedure:

  1. Turn the ignition switch to the OFF position.
  2. Detach the coolant temperature sensor electrical connector.
  3. Using a DVOM set to the ohms scale, connect one lead to terminal A and the other lead to terminal B of the coolant temperature sensor connector.
  1. With the engine at normal operating temperature, approximaterly 200 degrees F (93 degrees C), the ohmmeter should read approximately 700-1000 ohms.
  2. With the engine at room temperature, approximately 70 degrees F (21 degrees C), the ohmmeter should read approximately 7000-13,000 ohms.
  3. If not within specifications, replace the engine coolant temperature sensor.
  4. Test the resistance of the wiring harness between PCM terminal 26 and the sensor wiring harness connector. Also check for continuity between PCM connector terminal 43 and the sensor wiring harness connector. If the resistance measures greater than 1 ohm, repair the wiring harness as necessary.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

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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.

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