Remove the temperature sensor plug and measure the resistance of the sensor against ground with an ohmmeter.
Compare the measured value with the given one on the graph. Example: a meter at 20°C should show 2.2-2.8 kOhm; at 80°C the instrument should show 290-370 ohms.
Caution: Always measure at two or more different coolant temperatures. The sensor can also be removed for testing.
If the specified value is not reached, replace the sensor.