Why use an oscilloscope instead of a multimeter?
Short answer: A scope shows how voltage changes over time, so it reveals glitches, dropouts, noise and signal shape that a meter averages away.
A multimeter updates a few times per second and shows an average. Many automotive signals change thousands of times per second: crank and cam sensors, injector pulses, ignition events, network messages. A meter might show 2.5 volts on a sensor that is actually dropping out for a few milliseconds, which is enough to cause a stall or misfire.
A scope draws the signal as a waveform, voltage on the vertical axis and time on the horizontal. You can see the shape, frequency, duty cycle, and anything that does not belong. That makes it the right tool for intermittent faults, sensor signals, injector and coil testing, network checks and relative compression tests using a current probe.
Scopes have a learning curve, but you do not need to master everything at once. Start by capturing known-good patterns on healthy cars, so you have a reference when you see a bad one. Many scan tool platforms offer scope modules that share the same screen and save data together.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.