Description

Coolant Temperature Sensor Description

1. Fault Codes:
Coolant Temperature Sensor - Low out of range P0117
Coolant Temperature Sensor - High out of range P0118
Coolant Temperature Sensor - Warm up time fault P0125
Coolant Temperature Sensor - Falling temperature fault P0116

2. Monitoring Procedure
Problems with the coolant temperature sensor will be detected using a number of tests. A range check will test for input values outside expected limits. A time to warm-up test will check that the sensor is responding to the rise in coolant temperature caused by the engine running. The coolant temperature in stall is used to index a map of expected warm-up times. This checks that engine has gone into closed loop fuelling within a given time, (the coolant information is the only sensor it depends upon). A falling temperature test will check for abnormal falls in temperature once a temperature rise has been detected. This test uses a tracker which follows the normal coolant temperature rise but at a lower temperature. The tracker is not allowed to decrease and is limited at a maximum. If the measure coolant temperature falls below the tracker a fault is flagged. If the range tested is not passed then the appropriate fault count will be incremented, otherwise it will be decremented. If the count reaches a given threshold then a fault is present.

3. Primary Detection Parameter
Coolant Temperature - measured in Volts, the outcome of a potential divider calculation.

4. Fault Criteria Limits
Coolant Temperature - Low out of range 0.059 V - equivalent to 145�C
Coolant Temperature - High out of range 4.922 V - equivalent to -40�C
Coolant Temperature - Warm up time limit, [closed loop fuel] typically 90 seconds at 20° C start temperature
Coolant Temperature - Falling temperature tracking limit 65°C
Coolant Temperature-Warm up temperature 18° C
Coolant Temperature-Tracker Lag 25° C

5. Monitoring Conditions
The range check will take place whenever there is power to the ECU.
The warm-up time test will start each time the condition 'Engine_Running' is true.
The falling temperature test will start each time the condition 'Engine_Running' is true.

6. Monitoring Time Length / Frequency of Checks
The frequency of the Coolant Thermistor diagnostic is 2Hz.

7. Criteria for Storing Fault Code
Two successive trips where the Coolant Thermistor diagnostic indicates a failed water temperature sensor.

8. Criteria for Illuminating MIL
Two successive trips where the Coolant Thermistor diagnostic indicates a failed water temperature sensor.

9. Criteria for Determining Out of Range Input Signals
The coolant temperature thermistor is subject to maximum and minimum voltage limits of 0.211 V and 4.912 V respectively.