Which signal type is commonly used to ascertain engine speed in modern vehicles?

The tachometer signal is the correct choice for determining engine speed in modern vehicles. A tachometer measures the rotational speed of the engine's crankshaft and displays this information, usually in revolutions per minute (RPM). It provides drivers with real-time data on how hard the engine is working, which is crucial for performance tuning and monitoring engine health.

In contrast, while speedometer signals and vehicle speed signals generally refer to the speed of the vehicle based on wheel rotation, they do not directly measure engine RPM. The RPM signal, while it sounds relevant, typically refers to the same data as the tachometer but in a different context or format, which might not be as commonly recognized as the term "tachometer." The term "tachometer signal" is directly linked to measuring the engine's speed, providing the most accurate description of the function being queried.