What goes after the sideways triangle is like a voltmeter; it has a high input resistance, so it doesn't "load" the junction between the pull-up resistor and the sensor. The way to "diagnose" if the pull-up is missing, or if the ECU is not powered, or if you have an open sensor, is to temporarily disconnect the sensor from the ECU pin, and the using your DMM, measure the voltage between the ECU pin where you disconnected the sensor, and ground.
Here are the possibilities:
1. You see a steady DC voltage, like 5V or 3.3V. That means the ECU is powered, and the pull-up inside the ECU box is ok.
2. You see 0V, or a floating input to your DMM. That means the ECU is not powered, or the pull-up inside the ECU box is defective or open...
Now reconnect the sensor.
3. You see the ECU pin voltage drop to less than 1., above. That means the sensor is likely ok.
4. You see no change in the ECU pin voltage from 1., above. That means that the sensor is open. Disconnect the sensor again, and measure the Sensor resistance with your DMM set to OHMs mode; measure between the sensor wire and ground. A good sensor should read between a few tens of Ω to a few hundred Ω.