Cooling fan problems

Sounds like the sensor is not reading the coolant temp, or the computer is not accepting the data from the sensor.
Its possible you have air in the cooling system, or you have a problem with the computer.

Try installing a jumper across the N/O terminal at the relay socket. Temp sensor in the radiator or in the thermostat housing supplies the signal for the relay the other relay signal is supplied by A/C in on position. both fans will run continuous with A/C on. One fan runs intermittent relative to water temp. Be careful not to blow a head gasket. If you leave the jumpers in place, the fans will stop when the ignition is turned off, save the engine until you isolate the relay signal problem. then simply remove jumpers and reinstall the relays

Would turn the key on no need to start it and unplug the ect engine coolant temp sensor. If fans come on then suspect a faulty etc which may not turn on the engine light. Which engine is in the vehicle so I can help locate the ect which is usually by the thermostat housing.

The cooling fan is supposed to come on when the /ac compressor clutch cycles on, and off when it cycles off.
The idle speed kicks up to compensate for the additional a/c compressor load and the additional alternator load. usually, just the low speed comes on until it hits a much higher temperature.

the system should cycle 4 to 7 times/minute at 79 degrees F.

Here are some things to consider:(The PCM (engine computer) is NEVER defective, don't replace it). I don't think it is the ECT (engine coolant temp sensor) or the Cylinder Head Temp Sensor. Or the VSS or the MAF sensors.


The electronically controlled fan clutch is controlled by the powertrain control module (PCM) based upon requests for airflow to cool the engine, transmission and A/C condenser. If no cooling is required, the electronics permit the fan to spin at a slower speed yielding improved fuel economy.
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Inoperative or damaged:

• Electronically actuated fan clutch
• Electronically actuated fan clutch controller
• Wiring, connectors, relays or modules
• Engine Coolant Temperature (ECT) sensor (4.0L SOHC)
• Cylinder Head Temperature (CHT) sensor (4.6L [3V])
• Mass Air Flow (MAF) sensor
• Vehicle Speed Sensor (VSS)
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If the cause is not visually evident, connect the scan tool to the Data Link Connector (DLC).
Retrieve any DTC Codes (Diagnostic Test Code). Autozone will do for free.

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The cooling fan clutch actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, shearing of the fluid results in fan rotation.

The cooling fan clutch actuator valve is activated with a pulse width modulated (PWM) output signal from the powertrain control module (PCM). By opening and closing the fluid port valve, the PCM can control the cooling fan clutch speed. The cooling fan clutch speed is measured by a Hall-effect sensor and is monitored by the PCM during closed loop operation.

The PCM optimizes fan speed based on engine coolant temperature (ECT), engine oil temperature (EOT), transmission fluid temperature (TFT), intake air temperature (IAT), or air conditioning requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM monitors the fan speed through the Hall-effect sensor. If a fan speed increase is required, the PCM outputs the PWM signal to the fluid port, providing the required fan speed increase.

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I had a similar problem. Is your temperature gauge pegged to the right as very hot? Or reads always cold, even when hot. If it is a 3100 motor their is a coolant temperature gauge sending unit under the air breather intake that is right next to where you replace the thermostat.

Get a haynes repair manual at a parts dealer, Amazon, or your public library.
On the Chevrolet Lumina, Monte Carlo, & Impala FWD 1995 to 2005 it's under section 3-8 on page 3-6. It goes into great detail, and it's too complicated to explain here. If your sensor is bad, but the wires and fuses are good then the fans won't run.

Your second fan only runs when the air compressor is turning, If your ac compressor is not running then the sensor will not have the passenger fan run.
You have to see if the fan motors are good and then the wiring is good, and no fuses blown. You might blow fuses so have extra blue ones if I remember right. Recheck fuses after testing.

Chevy dealer says will not come on until temperature reaches 219 f

The computer turns on the fan. Based on sensors from the motor.
DTC P0480 - COOLING FAN CIRCUIT

Circuit Description

The cooling fan is controlled by PCM through the fan relay based on inputs from ECT sensor, IAT sensor, A/C selector switch, A/C refrigerant pressure switch and vehicle speed sensor. PCM controls cooling fan by grounding cooling fan control circuit which turns on cooling fan relay.

The fan relay will be commanded on when ECT reaches 223°F (106°C) or greater, A/C is requested or vehicle speed is less than 38 MPH. Cooling fan relay will also be commanded on regardless of vehicle speed when a DTC is set requesting cooling fan to be on, ECT is 304°F (151°C) or greater, or A/C refrigerant pressure is high. Cooling fan may also be commanded on when engine is not running, on certain conditions.

Conditions for setting DTC:

Battery voltage greater than 9.5 volts.

Cooling fan fault line detects a malfunction for 6 seconds.

1. Check cooling system. Ensure coolant level and belt tension are correct. Adjust/repair as necessary. After repairs, go to step 23). If no adjustment or repairs were required, go to next step.

2. Turn ignition on, with engine off. Using scan tool, check if cooling fan is operating with ECT at less than 209°F (98°C). If cooling fan is off, go to next step. If cooling fan is on, go to step 4).

3. Command cooling fan relay on. If cooling fan operates, go to step 23). If cooling fan does not operate, go to step 5).

4. Turn ignition off. Disconnect PCM harness connector. If cooling fan turns off, go to step 23). If cooling fan does not turn off, go to step 6).

5. Disconnect cooling fan relay harness connector. Using a test light connected to ground, probe battery feed circuits in relay harness connector. If test light illuminates on both terminals, go to step 7). If test light does not illuminate on both terminals, go to step .

6. Disconnect cooling fan relay harness connector. With test light connected to ground, probe battery feed circuit in relay harness connector. If test light illuminates, go to step 9). If test light does not illuminate, go to step 10).

7. Connect a jumper wire between cooling fan relay battery feed and cooling fan battery feed circuit. If cooling fan operates, go to step 11). If cooling fan does not operate, go to step 12).

8. Repair open in battery feed circuit. After repairs, go to step 23).

9. Repair short to voltage in cooling fan battery feed circuit. After repairs, go to step 23).

10. Connect test light battery voltage and probe cooling fan control circuit. If test light illuminates, go to step 13). If test light does not illuminate, go to step 21).

11. Connect test light to battery voltage and probe cooling fan control circuit. Using scan tool, command cooling fan on. If test light illuminates, go to step 14). If test light does not illuminate, go to step 15).

12. With jumper wire still connected, disconnect cooling fan harness connector. Using test light connected to ground, probe cooling fan battery feed circuit. If test light illuminates, go to step 16). If test light does not illuminate, go to step 17).

13. Repair short to ground in cooling fan control circuit. After repairs, go to step 23).

14. Check terminals to cooling fan relay. Repair as necessary. After repairs, go to step 23). If terminals are okay, go to step 21).

15. Check cooling fan control circuit for open or poor connection. Repair as necessary. After repairs, go to step 23). If circuit or connection is okay, go to step 22).

16. Connect test light to battery voltage and probe cooling fan ground circuit. If test light illuminates, go to step 1. If test light does not illuminate, go to step 19).

17. Repair open or poor connection in cooling fan ignition feed circuit. After repairs, go to step 23).

18. Check for poor connections at cooling fan harness connector. Repair as necessary. After repairs, go to step 23). If connections are okay, go to step 20).

19. Repair open or poor connection in cooling fan ground circuit. After repairs, go to step 23).

20. Replace cooling fan motor. After replacing cooling and motor, go step 23).

21. Replace cooling fan relay. After replacing relay, go to step 23).

22. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.

23. Turn ignition on, with engine off. Command cooling fan on. If cooling fan operates, system is okay. If cooling fan does not operate, repeat step 1).

Replace the coolant sensor,it turns the fan on when the temp gets to the 218 degree mark,and then it cuts it off.Make sure there is no air in the cooling system,if there is bleed it out.Check for a blown fuse also,and see if the fan will come on with the defrost,or ac,it should come on automatic if the ac is turned on,or defrost,if it does,replace the coolant sensor

chrysler to test find the ect....electronic cooling temperatute sensor a two wire sensor neer thermastat housing.. unplug it and with in a couple seconds fan should come on if they do replace sensor oem only.. if still not come on do they come on when ac on.... big problems with pcm....power train control module... main computer.. but cost alot of money so need to be sure......color of wires to ect are dark blue with dark green stripe second wire is violet with orange stripe....get back if not fix for more info

Yes there is a relay, but first answer this question, do you know the fans don't come on until the engine temp is above 230+ degrees F.? That is almost in the hot zone. run a scanner on the engine and watch the ECT sensor temp reading to verify proper cooling fan operation, a quick test to see if the system works is to unplug the ECT sensor, the fans will go into failure mode and turn on to avoid damage to the engine.