Thermostat Monitoring Sensor: Input/Output
The ECM provides the thermostat monitoring sensor with a 5 volt reference via pin 21 of connector C0635 of the ECM, and an earth via pin 5 of connector C0635 of the ECM.
There are three types of thermostat monitoring sensor diagnostic checks:
- Sensor signal is above maximum threshold. For the ECM to register this as a fault, and illuminate the MIL, the temperature registered by the thermostat monitoring sensor must be above 140°C (284°F) for more than 1 second.
- Sensor signal is below minimum threshold. For the ECM to register this as a fault, and illuminate the MIL, the temperature registered by the thermostat monitoring sensor must be below -33°C (-27°F) for more than 1 second, while the inlet air temperature reading is greater than -32°C (-25°F).
- Signal difference between ECT sensor and thermostat monitoring sensor is below maximum threshold. For the ECM to register this as a fault, and illuminate the MIL, the following conditions must exist:
- No maximum or minimum threshold signal faults exist.
- No faults are recorded against the thermostat monitoring sensor or vehicle speed signal.
- Engine not in idle speed control.
- Fuel cut-off not active.
- Engine speed is greater than 400 RPM.
- Road speed is greater than 0 mph.
- Integrated mass air flow from engine start to fuel cut-off is greater than set value (between 3 kg and 10 kg dependent upon engine coolant temperature at engine start).
- Engine coolant temperature at engine start is between 9°C and 39°C (48°F and 102°F).
- High range is selected.
- Delay time before thermostat monitoring is enabled is between set limits (between 50 and 500 seconds dependent upon engine coolant temperature at engine start).
- Engine coolant temperature is greater than 90°C (194°F).
- The difference between the ECT sensor reading and the thermostat monitoring sensor reading is less than 39°C (102°F).
Should a malfunction occur, the following fault codes may be evident and can be retrieved by TestBook/T4. See Fig 1.