Sensors tell the control unit what is happening on the machine, and actuators carry out its commands. When one of them misbehaves, the machine uses more fuel, loses power or acts unpredictably.
We measure the signals with a multimeter, oscilloscope and diagnostic tool, simulating operating conditions where needed, and compare the results with the manufacturer's values.
Typical findings are wrong readings, slow or jerky actuators and mismatches between systems.