5.10.1 Description
The engine coolant temperature is determined by the use of a temperature sensor, fitted in the cylinder head. The sensor is a temperature dependent resistor (thermistor), i.e. the resistance of the sensor varies with temperature. The thermistor is an Negative Temperature Co-efficient (NTC) type which means that the sensor resistance decreases as the sensor temperature increases.
The sensor forms part of a voltage divider chain with an additional (pull-up to 5V) resistor in the ECM. The voltage from this network changes as the sensor resistance changes, and hence the voltage measured by the ECM is related to the coolant temperature.
The coolant sensor information is used to adapt the fuelling and timing level of the engine with respect to engine temperature. This is to maintain performance and emissions as the engine temperature varies and is also used to ensure a good quality of engine start.
The data is also used by the instrument pack for the control of the coolant temperature gauge. This data is transmitted via CAN.
A fault condition is recognized if the ECT exceeds a minimum or maximum threshold, or the closed loop enable temperature has not been achieved within a temperature dependent time threshold.
| Component/System | Fault Codes | Monitoring Strategy Description | Malfunction Criteria | Threshold value | Secondary Parameter | Enable Conditions | Time Required | MIL Illumination |
|---|---|---|---|---|---|---|---|---|
| Engine Coolant Temperature Sensor | P0118 | Range check (minimum) | Implausible temperature | < - 38.3°C | If IAT Then wait for | < -5.25°C 10.0s after start | 2.5 s / continuous | two driving cycles |
| P0117 | Range check (maximum) | > 138°C | ||||||
| P0116 | Rationally check | Reaches closed loop enable temperature | from > 300 s at below -30°C to > 120 s at above 8.3°C | immediately / continuous | ||||
If the above table does not include details of the following enabling conditions: - IAT, ECT, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.