Engine Coolant Temperature (ECT) Sensor

Discovery

The ECT sensor is located on intake manifold, near thermostat housing. ECT sensor consists of a temperature dependent resistive metal strip. ECT sensor output voltage changes as engine coolant temperature changes. ECT works as a Negative Temperature Coefficient (NTC) sensor. As coolant temperature increases, sensor resistance decreases, as coolant temperature decreases, sensor resistance increases. See ECT SENSOR OUTPUT VOLTAGE table. ECM monitors ECT sensor resistance values and triggers enrichment circuits to extend injector on-time during cold starting and warm-up (a richer mixture at low coolant temperatures). ECM also uses ECT sensor values for Secondary Air Injection activation. See SECONDARY AIR INJECTION under AIR INJECTION SYSTEM.

Default strategy for ECT sensor is to select a substitute value based on intake air temperature. Initial ECT sensor default value selected will increase to a pre-warm up value over a time period programed for each default. An ECT sensor fault may result in a fast idle condition on initial start-up until fully warm value is reached. There may be a hot engine restart problem. The coolant temperature gauge may read excessively cold or hot. The engine cooling fan will not operate. A fault is indicated by illumination of the MIL.

ECT SENSOR OUTPUT VOLTAGE ⁽¹⁾

Coolant Temperature

Output Voltage

50°F (10°C)

4.2 Volts

86°F (30°C)

3.5 Volts

104°F (40°C)

2.8 Volts

158°F (70°C)

1.4 Volts

212°F (100°C)

0.6 Volt

266°F (130°C)

0.2 Volt

⁽¹⁾	ECT sensor values are approximate.

Freelander

The ECT sensor provides the ECM with a signal voltage that varies with coolant temperature, to enable the ECM to adapt fueling quantity and ignition timing with engine temperature changes. The ECT sensor is located between the cylinder banks, between cylinders No. 3 and 6. The ECT sensor is an encapsulated Negative Temperature Coefficient (NTC) thermistor which is in contact with engine coolant. As coolant temperature increases, resistance decreases, and as coolant temperature decreases, sensor resistance increases. To determine coolant temperature, the ECM supplies a regulated 5 volt power supply and monitors the return signal voltage. The ECM also outputs coolant temperature on CAN system, to operate coolant temperature gauge. If the ECT signal is missing, or outside an acceptable range, the ECM assumes a default temperature depicting a partially warm engine. This enables the engine to function with reduced driveability when cold and increased emissions, resulting from an over rich mixture, when the engine reaches normal operating temperature. The ECM will also switch on the cooling fans to prevent the engine and gearbox overheating.

Range Rover

The ECT sensor is located on intake manifold, near thermostat housing. ECT sensor consists of a temperature dependent resistive metal strip. ECT sensor output voltage changes as engine coolant temperature changes. ECT works as a Negative Temperature Coefficient (NTC) sensor. As coolant temperature increases, sensor resistance decreases, as coolant temperature decreases, sensor resistance increases. See ECT SENSOR OUTPUT VOLTAGE table. ECM monitors ECT sensor resistance values and triggers enrichment circuits to extend injector on-time during cold starting and warm-up (a richer mixture at low coolant temperatures). ECM also uses ECT sensor values for Secondary Air Injection activation. See SECONDARY AIR INJECTION under AIR INJECTION SYSTEM.
The ECT sensor connector has four wires. Two are signal and ground connections used by the ECM, the other two are used by the Body Control Module (BECM) for control of the coolant temperature warning lamp operation. The sensor contains two thermistors with negative temperature coefficients. As temperature increases, the thermistors resistance decreases, as coolant temperature decreases, sensor resistance increases. The ECM receives a corresponding analogue input voltage between zero and 5 volts.

If the ECT sensor fails, the ECM uses a substitute software routine that changes default value during warm-up. The ECM uses the signal from the inlet air temperature sensor when operating with the substitute software routine. When the software model reaches a coolant temperature of 140°F (60°C) the ECM employs a fixed default value of 185°F (85°C). The ECM coolant model also forms part of the diagnostics that is performed for detecting an ECT sensor fault, as well as open and short circuit tests.

An ECT circuit failure may result in: poor cold and warm/hot starting and driveability, instrument cluster temperature warning lamp will illuminate, MIL will illuminate, temperature gauge reads excessively hot or cold, cooling fan will not run, and Secondary Air Injection (SAI) pump will operate at engine start up even when engine is hot.