Engine Coolant Temperature (ECT) Sensor

Engine Coolant Temperature (ECT) Sensor

the ECT sensor is located front of the engine, adjacent to the thermostat housing. the sensor incorporates two Negative Temperature Coefficient (NTC) thermistors and four electrical connections. One set of connections are used by the ECM while the other set are used by the instrument pack temperature gauge.







Each thermistor used forms part of a voltage divider circuit operating with a regulated 5 V feed and an earth.

the signal supplied by the ECT sensor is critical to many fuel and ignition control strategies. Therefore, the ECM incorporates a complex ECT sensor default strategy which it implements in the event of failure. the ECM uses a software model, based on the time the engine has been running and the air intake temperature, to provide a changing default value during the engine warm-up. When the software model calculates the coolant temperature has reached 60°C, a fixed default value of 85°C is adopted for the remainder of the ignition cycle. the software model also forms part of the sensor diagnostics: if there is too great a difference between the temperatures from the sensor input and the software model, for more than 2.54 seconds, the ECM concludes there is a fault with the sensor input.

the following symptoms may be noticeable in the event of an ECT sensor failure:

- the MIL lamp illuminated
- Poor engine hot and cold start
- Instrument pack engine overheat warning lamp illuminated
- Excessively hot or cold reading on the temperature gauge.

At the time of a failure, the ECM will also store details of the engine speed, engine load and intake air temperature in its memory. This information is stored to aid diagnosis of the fault.