LW100 L4-2.2L VIN F (2002)
Temperature Vs Resistance Part 2
The ECT sensor is located in a coolant passage in the side of the cylinder head near the thermostat housing. 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 Temperature telltale illumination, coolant temperature gauge position and cooling fan operation (fan control 1 and 2 logic signals
to the cooling fan control module). The PCM also uses the ECT sensor for ignition timing, EVAP purge solenoid control, idle speed control and oil life
monitoring.
COOLING FAN(S) MOTOR CONTROL - The PCM controls both cooling fan motors at all times by independently grounding two logic circuits (fan
control 1 and fan control 2) to the cooling fan control module. When the PCM is not grounding a fan control circuit, the cooling fan control module will
detect a high voltage state (battery voltage). When the PCM is grounding a fan control circuit, the cooling fan control module will detect a low voltage
state (ground). The combination of these high/low voltage states at the cooling fan control module allows the PCM to command four different fan
speeds: Off, low, medium and high.
The PCM may ground fan control 1 and/or fan control 2 based on the reading from the ECT sensor. Under normal operating conditions, both cooling
fans operate on low speed whenever the ECT is greater than 99°C (210°F), on medium speed if the ECT is greater than 102°C (216°F) and on high
speed if the ECT is greater than 105°C (221°F). The cooling fans will turn Off when the temperature drops below 95°C (203°F). If the engine is turned
Off and the ECT is above 105°C (221°F), the cooling fans will run on low speed for 7 minutes regardless of how fast the ECT cools down. If the engine
is turned Off and the ECT is above 110°C (230°F), the cooling fans will run on low speed for 8.5 minutes regardless of how fast the ECT cools down. If
a low/high ECT sensor circuit fault (DTC P0117 or P0118) is set, the PCM will command the cooling fan control module to run the fans on high speed
to protect the engine and transaxle until the condition is corrected. The PCM also runs the cooling fans based on A/C high side pressure. Refer to the
HVAC for a cooling fan logic description on fan speed vs. A/C system pressure.
COOLANT TEMP GAUGE - The PCM controls the coolant temperature gauge by sending gauge position messages to the BCM over the Class II link
based on ECT sensor readings. The BCM averages the temperature over time allowing the gauge 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 gauge.
COOLANT TEMPERATURE TELLTALE - The Coolant Temperature telltale is used to alert the driver that the engine may be in an overheated
condition. The PCM controls the Coolant Temperature telltale by sending a message to the BCM, which sends a message to the I/P cluster over the Class
II link to turn On the telltale. 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 Temperature
telltale will NOT be illuminated. The cooling fans will be commanded On high.
