A wiring diagram turns a vague ‘sensor problem’ into a finite circuit. Identify the connector pin numbers, wire colors, power source, splice points, shared references, grounds and the control-module pins. Note whether the sensor is supplied with 5 V, battery voltage or a module-specific feed, and whether it shares that feed with other components.
Do not assume the diagram shows physical locations. Electrical schematics emphasize connectivity, while connector views and harness-routing diagrams show where things actually are. A splice drawn next to a sensor on the page may physically be a meter away inside a wrapped harness.
For diagnosis, mark expected measurements on the diagram before touching the vehicle: supply voltage, ground path and signal type. Then test from the easiest accessible point toward the module. If a sensor has good power and ground but no plausible signal, test the signal at both sensor and ECU ends before deciding the sensor is bad.
When several sensors share a reference or ground, the diagram immediately suggests a branch-isolation strategy. This is one reason professional diagnosis starts with information rather than parts.
Figure: How to Read Sensor Wiring Diagrams