Automotive sensors do not all speak the same electrical language. Many older and simpler sensors use an analog voltage. A throttle-position sensor might move through a low-to-high voltage range as the throttle opens. A pressure sensor may use a similar voltage range but represent pressure instead of angle. The ECU measures that voltage and converts it into engineering units.
Speed and position sensors often use frequency. The faster a shaft or wheel rotates, the more pulses arrive each second. Some sensors use pulse width or duty cycle, where the percentage of time a signal is high carries the information. A digital sensor can also send structured messages rather than a continuously changing voltage. This is common in newer vehicles where a smart sensor contains its own electronics.
The testing consequence is important. A multimeter can show an average voltage that looks reasonable while missing a distorted pulse train. A scan tool can show a calculated value but hide an intermittent electrical glitch. An oscilloscope is ideal for waveform quality, yet beginners can still diagnose many faults by combining scan data, a multimeter, visual inspection and careful comparisons.
Before testing, determine what kind of signal is expected. Do not apply resistance mode to a powered electronic sensor, and do not assume every three-wire sensor is simply 5 V, ground and analog output. Wiring diagrams and manufacturer information take priority over generic expectations.