Engine Coolant Temperature (ECT) Sensor - (From 99MY)
The ECT sensor is located at the top front of the engine, adjacent to the coolant outlet pipe. The sensor screws into a thread in the inlet manifold and incorporates a sealing ring between the faces of the sensor and manifold.
The ECT sensor multiplug has four wires; two are the signal and ground connections used by the ECM, the other two are used by the body control module (BeCM) for control of the temperature warning lamp operation on the instrument pack.
The sensor contains two thermistors with negative temperature CO-efficient; as temperature increases, the thermistor's resistance decreases. The ECM receives a corresponding analogue input voltage between 0 and 5V.
NOTE: The temperature/resistance characteristics of the two thermistors differ, and so it is important to maintain the correct pin-outs.
The ECM uses the information received from the ECT sensor to make adjustments to the engine operating conditions. The ECM ensures a richer air:fuel mixture is available at lower block temperatures for good quality starts and smooth running. The mixture is then made leaner as the engine temperature rises to maintain low emissions and good performance.
If the sensor fails, the ECM uses a substitute software routine that changes default value during warm up, based on the signal from the inlet air temperature sensor. When the software model reaches a coolant temperature of 60°C (140°F) the ECM implements a fixed default value of 85°C (185°F). The ECM coolant model also forms part of the diagnostics that is performed for detecting a temperature sensor fault, as well as open and short circuit tests.
Temperature Voltage
-50° C 5V
-20° C 4.8V
10° C 4.2V
40° C 2.8V
70° C 1.4V
100° C 0.6V
130° C 0.2V
NOTE: All voltages listed are approximate.
A coolant temperature circuit failure may result in the following symptoms:
- Poor cold and warm/hot starting and driveability.
- Instrument pack temperature warning lamp will illuminate.
- MIL will be illuminated.
The ECT sensor can fail in the following ways, or supply an incorrect signal:
- Sensor open circuit.
- Short circuit to vehicle supply.
- Short circuit to earth.
- Incorrect mechanical fitting.
- Signal fixed above 40°C (140°F) not detected.
- Signal fixed below 40°C (140°F) not detected.
Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by Testbook:
- P0116 - (Signal differs too much from temperature model for longer than 2.54s)
- P0117- (Open circuit or short circuit to battery supply)
- P0118 - (Short circuit to ground)