Note. An ohmmeter is required to check the correctness.
Examination
1. On the F8Q 620 engine, the sensor has two functions. The NTC resistor notifies the heater control unit of the coolant temperature, and the switch cuts off power to the EGR solenoid valve. On turbocharged F8Q and F9Q engines, the sensor has only one function - it informs the injection ECU about the temperature of the coolant. In both cases, the sensor must first be removed as described below, and then it can be checked.
2. On the F8Q 620 engine, connect an ohmmeter to pins 1 and 4 of the sensor connector. At room temperature, the resistance should be infinite, i.e. thermal switch contacts are open.
3. Then tie a twine to the sensor and lower it into a container of water (it should not touch the walls or bottom of the container). Immerse the thermometer in water and start heating it. Check that the thermal switch contacts remain open up to 20°C and close at 30°C. With closed contacts, the ohmmeter should show zero resistance.
4. On all motors, connect an ohmmeter to terminals 2 and 3 of the (there are only two terminals on the F9Q motor). Heat the water and check that the resistance of the thermistor (coolant temperature sensor) is in accordance with the data given in Specifications.
5. If the results obtained are not satisfactory, the switch is defective and must be replaced.
Attention! Remove the temperature sensor only from a cold engine.
Removing
1. The sensor is attached to the thermostat housing, on the left side of the cylinder head. It has a black connector on the F8Q engine, or a white one on the F8Q engine with a turbocharger.
2. Drain the liquid from the cooling system as described in Chapter Maintenance. Alternatively, prepare a new sensor or a suitable plug to quickly plug the hole and prevent fluid from escaping.
3. Disconnect the connector, then unscrew the sensor. Remove the sealing ring.
Installation
1. Install in reverse order, use a new O-ring.
2. Finally, fill and bleed the cooling system as described in Chapter Maintenance.