ENGINE COOLANT TEMPERATURE (ECT) SENSOR
Description
The Engine Coolant Temperature (ECT) sensor is mounted in the engine coolant stream (figure 5-23). The PCM uses coolant temperature as an indicator of engine operating temperature.
The sensor is a thermistor that changes value based on temperature. Low coolant temperature produces high resistance; high coolant temperature produces low resistance.
The chart below shows sensor resistance values, as well as sensor voltage signals as read by the PCM, at various temperatures.
ECT Sensor Circuit Operation
The Engine Coolant Temperature (ECT) sensor receives a 5 volt signal on PCM CKT 410 (figure 5-24). As coolant temperature rises or falls, ECT sensor resistance changes inversely. When the engine is cold, sensor resistance is high. Conversely, when the engine is hot, sensor resistance is low.
As ECT sensor resistance changes, it affects the strength of the voltage signal on CKT 410. The PCM monitors this signal and uses it to determine coolant temperature. Voltage on the circuit will range from almost 5 volts at low temperatures to less than 1 volt at high temperatures.
The ECT sensor shares a common ground with the intake air temperature sensor, crankshaft position sensor, and boost sensor on CKT 452.
Engine coolant temperature affects most systems controlled by the PCM
DTC 14 — “Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temperature Indicated)”
DTC 14 sets when coolant temperature is greater than 151°C (304°F) for longer than 2 seconds. This high temperature would cause low voltage on the circuit as read by the PCM. If a DTC 14 condition is detected, the PCM substitutes an ECT default value of 77°C (171 °F) and fast idle.
DTC 14 could also be caused by a short in CKT 410 to ground.
DTC 15 — “Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temperature Indicated)”
DTC 15 sets when coolant temperature is less than -36°C (-33°F) and the engine has been running for at least 8 minutes. This condition would cause excessive high voltage on the circuit as read by the PCM The PCM default value for this code is 18°C (64°F).