Question about 2003 Mercury Grand Marquis

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Coolant fan not coming - 2003 Mercury Grand Marquis

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  • Mercury Master
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Hi.

If you are referring to the climate control blower fan, the one blowing hot and cold air from the heater core inside the vehicle, then check 40 amp fuse (F1.103) and the blower relay in the battery fuse box. Then check the additionally 15 amp fuse (F2.15) for blower motor in central fuse box.
If fuses are OK, check the blower motor speed controller. The blower motor speed controller is located in correspondence of the blower/evap housing, at the center of the dash. Test if there is ground to the motor. If there is no ground to motor, or if the controller does not supply voltage to motor, replace the controller.

If we are instead talking about the radiator fan, then the problem is usually the ECT (Engine Coolant temperature sensor -someone calls it thermostat). Before replacing the ECT sensor, you can check the fan motor itself, by reading if there is voltage at the motor. If there is voltage and fan does not run, then the problem is not ECT sensor but fan motor.

In this engine the fan is directly controlled by the PCM through the signal from temperature sensor:"
The Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.
The Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT is a two-wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature."

If the motor and relays test fine, then replace the ECT sensor. In the 2003 model the ECT sensor should be located on the rear of the engine block below the intake manifold. See the pictures at the bottom of this page showing a thermostat in a 1997 model.

Posted on May 20, 2011

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Could be the temp sensor, low coolant, or the fan relay.
The temp sensor tells the computer how hot the engine is and the computer grounds the fan relay. It should come on around 230 degrees.

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You need to change the relay and the temp sensor switch. If you have done that the reason it's not coming on is probably because the coolant is not getting hot enough to cause it to come on. Let me explain. The coolant fan when the A/C is off is activated by the coolant fan switch. The switch closes when coolant temperature is over 238F completing a path to ground through the coolant fan relay windings. The relay contacts then close and voltage is applied to the coolant fan. When the coolant temperature drops to 214F, the switch opens and the coolant fan stops. In A/C equipped vehicles, the A/C control head completes a path to ground for the coolant fan relay whenever the A/C is on no matter what the temperature. Voltage is then applied to the coolant fan. Essentially, the coolant fan switch is by-passed when the A/C is on, which is why the fan works whenever you turn the A/C on. Now, if the fan does not kick in when the coolant temperature is over 238F but works when the A/C is on, the problem has to be the coolant fan switch or the connectors or wiring to the CFS.

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Engine fan won't come on


IF COOLANT FAN FUSE AND RELAY OKAY.HOT WIRE COOLANT FAN TO SEE IF FAN MOTOR OKAY.IF FAN MOTOR OKAY.THE ENGINE COOLANT TEMPERATURE SENSOR MORE LIKELY BAD.THE ENGINE COOLANT SENSOR WHEN ENGINE COOLANT GETS HOT IT CAUSES ENGINE COOLANT TEMPERATURE RESISTANCE TO DECREASE CAUSE COMPLETE CIRCUIT IN WHICH POWER FROM PCM TO ECT SENSOR WILL SENT POWER TO COOLANT FAN RELAY THEN CAUSE COOLANT FAN TO TURN ON. HAVE ECT SENSOR OR ENGINE COOLANT TEMPERATURE SENSOR CHECK USING CODE SCANNER TO MAKE SURE ITS WORKING BEFORE SPENDING EXCESS MONEY.

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My 2007 Impala LS says its overheating shut off A/C the temp gauge goes all the way up then in an instant comes back down to normal


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scan car to see witch problem code it is, any auto parts store will scan for free. check for 12 volts at coolant fans connection. if your getting voltage then the fans may be bad.

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with the a/c on, the fan should be on. crank it up, turn a/c on, now take a hammer and gently tap on the coolant fan, if it comes on, or attempt to spin, its bad.

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