2002 Saturn SL cooling fan

Here is some information from the service manual for your machine that may help you figure out what's going on:

Engine Coolant Temperature (ECT) Sensor

The ECT sensor is located in a coolant passage in the side of the cylinder head near the upper radiator hose. The ECT sensor is a two wire thermistor type sensor that varies resistance according to changes in engine coolant temperature. The PCM supplies a five volt reference through a resistor to the sensor, which is connected to ground. When the sensor is cold it has high resistance, high signal voltage at PCM. As the sensor temperature increases, its resistance decreases, lower signal voltage at PCM. The PCM uses the signal voltage to determine engine coolant temperature.

The ECT sensor is used by the PCM for fuel control, calculation of temperature of air/fuel mixture at the intake valve in conjunction with the IAT sensor temperature, Coolant Temp telltale illumination, coolant temperature gage position and cooling fan relay operation. The PCM also uses the ECT sensor for ignition timing, exhaust gas recirculation (EGR) operation, evaporative emission (EVAP) purge solenoid control, idle speed control and oil life monitoring.

COOLING FAN MOTOR CONTROL The PCM controls the cooling fan motor by grounding the cooling fan relay. When the relay coil circuit is grounded, the switch side of the relay closes allowing current to flow to the cooling fan motor.

The PCM operates the cooling fan relay based on the reading from the ECT sensor. Under normal operating conditions, the cooling fan operates whenever the ECT is greater than 105.5°C (226°F) or the A/C relay is commanded ON below 113 km/h (70 mph). The cooling fan will turn OFF when the temperature drops below 100°C (212°F). If the engine is turned OFF and the ECT is above

107°C (225°F), the cooling fan can run up to 4 minutes or until the ECT drops below 107°C (225°F). If a low/high ECT circuit fault (DTC P0117 or P0118) is set, the PCM will command the cooling fan relay ON to protect the engine and transaxle until the condition is corrected.

Degrees(°F) Sensor Resistance(ohms)

-40 77k-109k

-20 39k-53k 0 21k-27k 20 11k-15k 40 6.6k-8.4k 60 3.9k-4.5k 80 2.4k-2.7k

100 1.5k-1.7k 120 0.98k-1.1k 140 650-730 160 430-480 180 302-334 200 215-235 220 159-172 248 104-113 284 63-68

COOLANT TEMP GAUGE The PCM controls the coolant temperature gage by sending gage position messages to the BCM over the class 2 link based on ECT sensor readings. The body control module (BCM) averages the temperature over time allowing the gage to move slowly and remain in a relatively stable position as temperature varies. The BCM then sends the averaged information to the I/P cluster over the link to position the gage.

COOLANT TEMP TELLTALE The Coolant Temp telltale is used to alert the driver that the engine may be in an overheated condition. The PCM controls the Coolant Temp telltale by sending a message to the I/P cluster over the class 2 link. The PCM will send the message when the ECT sensor reading is above 118°C (244°F). If this condition exists, the PCM will set DTC P0217. If a high temp/low voltage fault exists in the ECT sensor circuit, the signal is considered invalid and the Coolant Temp telltale will not be illuminated. The malfunction indicator lamp (MIL) and cooling fan relay will be commanded ON, however.

Thank you very much for that information. I replaced the ECT sensor and changed and flushed the coolant on Sunday and so far the fan is functioning properly. Can I ask what the source was for the information you posted? I only have the Hanes manual and it has been less than complete and confusing at times?

The information came from the Techline CDs produced by eSI, one of GM's entities. There are six CDs in the set and they have the exact same information on them as you would find in the official Helms paper service manuals. Got them on eBay. They cover 1998 to 2005 GM vehicles. Great bargain.