Sensor Types and Signals

Analog, digital, resistive and inductive sensors — and how each fails.

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What you will learn

Classify sensors by output type
Explain reference voltage and signal return
Predict the scope trace for each family

Sensors convert a physical quantity — pressure, temperature, position, speed, gas concentration — into an electrical signal the ECU can read. The family of the sensor determines how you test it: a resistive sensor is measured with an ohmmeter, while a Hall or inductive sensor is tested with a scope or a live-data reading.

A crucial idea: most sensors do not create a voltage from nothing. The ECU supplies a regulated reference (often around 5 V) and a signal return, and the sensor modulates the signal against its ground. If the reference or the ground is wrong, every reading is wrong.

Family	Example	Output	Best test
Resistive (potentiometer)	Throttle position	Voltage divider	Sweep with ohmmeter or scope
Thermistor (NTC)	Coolant temperature	Resistance vs temperature	Resistance at known temperatures
Hall effect	Camshaft / wheel speed	Digital square wave	Scope or live data
Inductive (magnetic)	Crankshaft / ABS	AC sine wave	Scope, AC volts, resistance
Piezo	Knock / rail pressure	Charge pulse	Scope with correct attenuator
Wideband oxygen	Lambda	Current pump	Live data and scope

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Key points

Most sensors are powered by a regulated reference voltage
Pots, thermistors, Hall and inductive sensors behave differently
The signal is only as good as its reference and ground

All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.