1998 Saturn S-Series
Cooling System Description Cooling Fan Motor Control
The PCM controls the cooling fan motor by controlling the cooling fan=20 relay. The PCM controls the cooling fan relay by controlling an internal=20 driver that pulls the relay coil circuit to ground. When the relay coil=20 circuit is pulled to ground, the switch side of the relay closes=20 allowing current to flow to the cooling fan motor.
The PCM turns the cooling fan relay ON based on the reading from the=20 engine coolant temperature (ECT) sensor. The ECT sensor is a thermistor=20 that varies resistance according to changes in engine coolant=20 temperature. The PCM supplies a 5 volt reference through a pull-up=20 resistor to the sensor, which is connected to ground. When the sensor is=20 cold, it has high internal resistance, high signal voltage at the PCM.=20 As the sensor temperature increases, its resistance decreases, a low=20 signal voltage at the PCM. The PCM uses the signal voltage to determine=20 the engine coolant temperature.
Under normal operating conditions, the cooling fan motor operates=20 whenever the ECT is greater than 105.5=B0C (222=B0F) or the A/C relay is=20 commanded ON below 113 km/h (70 mph). The cooling fan motor will turn=20 OFF when the temperature drops below 100=B0C (212=B0F). If the engine is=20 turned OFF and the ECT is above 107=B0C (225=B0F), the cooling fan motor ca= n=20 run up to 4 minutes or run until the ECT drops below 107=B0C (225=B0F) with= =20 the ignition OFF. If a low/high ECT circuit fault resulting in DTC P0117=20 or P0118 is set, the PCM will command the cooling fan relay ON to=20 protect the engine and transaxle until the condition is corrected. Coolant Temp Gage
The PCM controls the coolant temp gage by sending a gage position=20 message to the instrument panel (IP) cluster over the Class II link. The=20 PCM receives the engine coolant temperature from the ECT sensor. The=20 gage position for the temperature is buffered, which means the=20 temperature is averaged over a period of time. This allows the gage to=20 move slowly and remain in a relatively stable position as the=20 temperature varies while driving. Coolant Temp Telltale
The coolant temp telltale is used to alert the driver that the engine or=20 transaxle may be in an overheated condition. The PCM controls the=20 coolant temp telltale by sending a message over the Class II link to the=20 I/P cluster to turn the telltale ON. The PCM will command the telltale=20 ON when the ECT sensor reading is above 118=B0C (244=B0F) or the transaxle= =20 fluid temperature (TFT) sensor reading is above 140=B0C (284=B0F). If this= =20 condition exists, the PCM will set DTC P0217 for the ECT and P0218 for=20 the TFT. If a low or high voltage circuit fault exists in either=20 circuit, the signal will be invalid and the PCM will NOT turn ON the=20 coolant temp telltale. The malfunction indicator lamp (MIL) and engine=20 cooling fan relay will be command ON, however. Coolant Level Telltale
The coolant level telltale is used to alert the driver that the coolant=20 level in the coolant recovery reservoir is low. Low coolant level is=20 detected by the low engine coolant level switch in the bottom of the=20 coolant surge tank. The switch closes when the coolant level in the=20 bottle is full. The switch is supplied ignition voltage from the UHFB=20 and this ignition voltage input is fed directly to the PCM. If the=20 engine is running and the voltage at the PCM is low, indicating no=20 coolant in the coolant surge tank, switch open, the PCM will command the=20 I/P cluster over the Class II link to turn the coolant level telltale=20 ON. If this condition exists for a certain length of time, the PCM will=20 set DTC P1620. Scan Tool Diagnostics
- The engine coolant temperature (ECT) can be read on the scan tool=20 in degrees C or F. * LOW COOLANT LEVEL can be read on the scan tool as YES or NO. * The scan tool can "Sweep" all gages to verify the coolant temp=20 gage can move from cold to hot. * The scan tool can turn ON all I/P cluster lights to verify the=20 coolant temp telltale can be turned ON and OFF.
Cooling System
Object Number: 872988 Size: MF Click here for detailed picture of above image.
The Saturn cooling system has two unique features, a coolant surge tank=20 and an inlet side thermostat. The system is filled through the pressure=20 cap and doesn't require any bleeding. Flow from the tank fills the=20 engine cylinder block, radiator, heater core, and hoses.
During engine operation with the thermostat closed, coolant is pumped=20 through the cylinder block, cylinder head, heater core inlet hose,=20 heater core, heater outlet hose, and back to the thermostat housing.=20 Coolant flows past the thermostat element and back to the water pump=20 inlet. Some coolant is routed back through the engine block to the=20 thermostat cavity. A thermostat by-pass valve controls return coolant=20 flow through the cylinder block and dampens sudden coolant pressure=20 surges by venting coolant back to the water pump suction side.
When the thermostat begins to open the by-pass valve begins to close the=20 cylinder block passage. Coolant flow is then routed from the pump=20 through the cylinder block, head, heater inlet, heater core, heater=20 outlet, and back to the cylinder block. Coolant is also routed through=20 the upper radiator hose, radiator core, lower or outlet radiator hose=20 past the thermostat to the water pump. Coolant flow from the heater=20 return and lower radiator hose wash the thermostat element, thus=20 regulating coolant flow through the lower radiator hose and to the water=20 pump.
Important
During extremely cold weather, -12=B0C (+10=B0F) or colder, the engine's=20 coolant temperature will decrease quickly when idling with the heater=20 fan on high speed, and cool air may flow from the heater outlet.
The fan control switch should be set at a slower speed position, fan=20 speed I or II, to maintain the hottest air flow.
The Saturn cooling system is filled with DEX-COOL=3D3F, a non phosphate,=20 silicate free ethylene glycol-based antifreeze recommended for aluminum=20 engine protection and increased water pump seal life. Coolant Surge Tank
Object Number: 872303 Size: MF Click here for detailed picture of above image.
The coolant surge tank is made of molded plastic. It incorporates a low=20 coolant sensor. This sensor is designed to signal a low coolant level=20 within the reservoir through a light on the dash. A magnetic float=20 assembly moves up and down with the coolant. An electrical switch is=20 held in the closed position by the magnetic float. When the coolant=20 level drops below a pre-determined point, the float assembly drops and=20 opens the switch, which triggers the low coolant light. Engine Cooling Fan
Object Number: 873183 Size: MF Click here for detailed picture of above image.
The A/C fan is 290 mm (11.6 in) long with five unequally spaced blades=20 to provide air flow through the radiator/condenser. The fan is driven by=20 an electric motor which is attached to the fan shroud.
A fan control relay is used by the PCM to control engine cooling fan=20 operation. The engine cooling fan is turned ON or OFF by the PCM=20 dependent upon engine coolant temperature, vehicle speed, or A/C ON=20 request. Under high ambient conditions, the fan may run up to four=20 minutes with the key OFF. Radiator
Object Number: 872929 Size: MF Click here for detailed picture of above image.
A cross-flow radiator is used on all models. Tanks on this type radiator=20 are located to the right and left of the core.
All service radiators have oil coolers with inlet outlet fittings for=20 transaxle fluid circulation. On vehicles equipped with a manual=20 transaxle, keep plugs on cooler fittings.