On my 2001 Focus Zetec 2.0L, the radiator fan only worked with the air conditioning turned on (as in no low speed - engine would overheat while idling or in traffic, but was fine as long as the A/C was on). The fix was to replace the radiator fan resistor assembly located in the fan shroud between the fans.
The fan should not come on at 104 unless you have the a/c turned on. Before you go tearing the harness apart, hit the simple things. How many miles are on it? is the cooling system in good condition; coolant, thermostat, radiator flow? Is it possible the cooling system has an air pocket in it, it is very common and will cause am overheat every time.Is it actually overheating in the first place? Newer cars run at 220-245*f . Check it with a temp probe, (in the coolant) if its not that hot and its pushing out coolant its a flow problem or possibly cylinder pressure pushing the coolant out (head gasket).
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Re: ENGINE COOLANT FAN NOT CUTTING IN
Hi firstly check your fuses if ok check the cooling fan wire it direct to the battery see if it works if ok find the tempeture switch which operates the fan by connecting both wires together with ignition on see if fan works if not the relay is next after that you arse looking at wiring looms rubed through or bad grounds yates210456
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possibly change the wrong unit
gauges work from a sender unit not a sensor
it is located next to the thermostat housing normally and has only 1 wire connection
they work by having power through the gauge to the sender through variable resistance that is affected by heat to ground
test disconnect the wire from the sender
turn on the ignition key , ground out the wire and the gauge should go straight to full hot
sensors on the other hand have more wires and relay the coolant temp to the ECM so that air/fuel ratios can be adjusted , and fans switched on as required
What make , model an year vehicle ? The PCM / ECM engine computer controls that relay . The best way to diagnose this is to hook up a scan tool an see if the PCM / ECM can control ( turn on ) the relay ! I'm going to ask a silly question , what are you going by to determine the vehicle is over heating ? The Temperature gauge . Temp. gauges do go bad . Hooking up a professional grade scan tool that can read engine sensor data PID'S is the way to see what the PCM/ECM is seeing as far as engine temp. Most vehicles the cooling fans don't come on till 200 to 220 degrees ! You could buy a temp gun at harbor freight an see what the temp is at the upper rad. hose .
The fan only operates when the engine/coolant temperature exceeds the thermostatically controlled fan. At idle observe the dash engine temperature and fan. Before the gauge reads above normal the fan should operate.
The ECM doesn't read the temps. it only takes the readings from the sensors and tries to adjust within given parameters. You has a coolant sensor on the car you have a temp sensor on the car. Check the wiring, make sure you didn't plug the wrong wire to the wrong sensor. Check to make sure everything is actually plugged in and getting power. It's definitely either bad wiring or a bad temp sensor.
sound like thermostat sticking close.replace thermostat and radiator pressure cap.if already done.you could have faulty water pump.if engine overheating at long slow traffic line or setting at a stand still.the engine cooling fans should be running, check and see if cooling fans running if not,check cooling fans fuses and relays.if all is good,hot wire make sure coolings fans okay.if all is good,code scan vechicle for faulty engine coolant temperature sensor and ecm problems.you need a code scanner where you can check live data check see if coolant temperature sensor reading correctly if engine coolant temperature is 190 degrees the coolant sensor. the scanner suppose to show 190 degrees in temperature if not it reads 80 or 90 degrees the engine coolant temperature sensor is faulty need replacing.if all is good check engine oil if look like milk shake blow head gasket will cause over heating.to be on the safe side i would replace thermostat and radiator pressure cap first.to make sure engine coolant circulating through radiator and engine block.
The ECM gets it messages for heat from the engine coolant temperature sensor. The sensor is probably bad. Since the fans come on right away the ECM is in a safe mode for the engine. Meaning it turns the fans on because it can't read the coolant sensor. As far as the fans staying on for a couple of minutes this is normal when the engine is hot. The ECM does this.
Your cooling fan relays are controlled by the Engine Control Module (ECM). What you are unplugging is probably the Engine Coolant Temperature Sensor (ECT). The ECM will default to "fans on" if it loses the circuit to the ECT. (It loses it when you unplug it) This is why the fans come on when you unplug the connector. The engine might be overheating because the ECT may be malfunctioning and "lying" to the computer about what the actual engine temperature is. If this is the case, the ECM is not turning the fans on because it doesn't "think" it is hot enough to need them. Then again, you could have a faulty temperature gauge that is making you think the engine is overheating when it is not. (If it is boiling over, then it is OBVIOUSLY overheating and you can just disregard that last statement.)
Anyway, the only way to properly diagnose the cooling system on your vehicle is to access the live engine data and look to see what temperature the ECM is seing while you take an actual reading with an infrared thermometer or a pyrometer and compare the two. Yhe thermometer or prometer reading should be within about 5 degrees of what the ECM "thinks" the temperature is. If there is a larger error than this then the coolant temp sensor should be replaced. If the reading is within this range and the temperatur gauge reads hot when it is not, then the gauge should be replaced.
Since the fans come on when you unplug the sensor, you know that all the fan circuits are working and the ECM is capable of controlling them, so it almost has to be a computer INPUT problem, not an OUTPUT problem.
The car overheats because the fan system is not working. The engine coolant sensor tells the computer to turn on the fan when it gets hot and also sends temperature readings through the computer to the heat gauge. Try turning the AC on if you have it--it should immediately start the cooling fan. If nothing, check the fan fuse and relay. It's also possible that the fan motor is frozen due to bad bearings. Try replacing the coolant temperature sensor to see if that restores the gauge readings. Hope some of this helps!
Your heater blower, inside the car works to provide heat to the interior of your car, and the air is hot, right? If the cooling fan is not coming on, depending on the outside ambient temperature, you may be using your heater coil for the heater to dispell suficient heat (inside the car), combined with a low outside temperature to keep the engine at normal operating temperature negating the need for the cooling fan. OR your coolant temperature sensor is bad, and the ECU doesn't know that the engine is hot and to turn on the fan. This sensor works by changing the voltage returned to the ECU depending on the temperature of the tip, which changes the resistance to the computers inquiry. So, the computer knows the temp of the coolant. It uses this information to adjust mixture gauge etc. Most now have 2. One for the gauge, and another for the ECU. So don't go by the gauge working. Then there is the fan motor itself. This can be tested by using a testlight on the wires when the engine temperature gauge in at 3/4 to the hot side of the gauge. The other way to test is to bring a live wire to the motor. If the motor is good, the sensor is bad, if the motor is bad, well the motors bad. I hope this helps you, write back if you need additional assistance. . Please take the time to rate our free service, and my performance. Thank you for trying FixYa.com!
The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine. Fig. 1: View of the Engine Coolant Temperature (ECT) sensorFig. 2: Engine Coolant Temperature (ECT) sensor locationTESTING
See Figures 3 and 4
Remove the ECT sensor from the vehicle.
Immerse the tip of the sensor in container of water.
Connect a digital ohmmeter to the two terminals of the sensor.
Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the engine coolant sensor temperature vs. resistance illustration.
Repeat the test at two other temperature points, heating or cooling the water as necessary.
If the sensor does not meet specification, it must be replaced.
Fig. 3: Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor wiring diagramFig. 4: ECT sensor temperature vs. resistance values