Electric Thermostat
| ITEM | DESCRIPTION |
|---|---|
| 1 | Engine Coolant Temperature (ECT) sensor |
| 2 | Heater element |
The electric thermostat is located on the front side of the cylinder block, below the intake manifold.
The electric thermostat independently controls the engine coolant flow in the cylinder block, improving engine warm-up times. The thermostat housing contains a wax expansion element. Inside the wax element is a heater element. When energized the heating element heats the wax element, partially controlling the thermostat function along with engine coolant temperature control. Operation is therefore performed not only by the engine coolant temperature, but as specified by the Powertrain Control Module (PCM). This method provides a finer control of the opening and closing of the electric thermostat.
Operation of the electric thermostat is controlled by the PCM upon the following inputs:
Engine load
Vehicle speed
Engine coolant temperature
Intake air temperature.
The electric thermostat has:
A startup battery feed from the Battery Junction Box (BJB) located in the left of the engine compartment beside the startup battery.
A switched power supply from the PCM relay, located in the BJB.
A hardwired connection to the PCM.
A ground connection.
When the PCM starts to regulate the system, the PCM supplies a ground path for the heater element in the electric thermostat. This causes the element to expand and increase the opening dimension of the electric thermostat.
The Engine Coolant Temperature (ECT) sensor is located in the electric thermostat housing. The sensor is sealed in the thermostat housing with an O-ring seal. The sensor is a push fit in the thermostat housing and rotated clockwise to lock in position.
The ECT sensor monitors the engine coolant temperature in the thermostat housing and uses the information to control the electric thermostat.
The ECT sensor circuit consists of a voltage divider which incorporates a Negative Temperature Coefficient (NTC) type sensor. The input to the ECT sensor is a 5 V reference voltage supplied through a resistor within the PCM. The ground from the ECT sensor is also connected to the PCM which measures the voltage across the ECT sensor. As the engine coolant temperature rises the resistance of the ECT sensor decreases and vice versa. The PCM calculates the engine coolant temperature from a map of sensor voltage against temperature.