Two-wire temperature and resistive sensors

CORE TEACHING Thermistor NTC/PTC concept; pull-up resistor inside ECU; two-wire circuit; open and short behaviour; resistance vs temperature. PRACTICAL DEMONSTRATIONS AND TESTS Read live temp; measure signal voltage; unplug sensor; bridge carefully for demonstration; resistance test sensor at different temperatures. ADVANCED / SCAN TOOL LAYER Scope is less essential but can reveal intermittents; graph live data during warm-up. KEY DIAGNOSTIC QUESTIONS Does reading match reality? Is sensor open, shorted, or just biased? Does wiring change the same way as sensor? MUST-COVER CHECKPOINTS Identify sensor technology; supply/ground if applicable; expected signal type; physical stimulus; scan comparison; scope if time-varying; wiring-to-ECU proof.

Coolant temperature reads -40°C on a warm engine. Why does an open circuit often create an extreme value?

Builds on

Lesson 19: Testing a three-wire sensor

Feeds into

Lesson 21: Hall-effect cam and crank sensors

1. 18Power, ground and signal — the universal sensor pattern
2. 19Testing a three-wire sensor
3. 20Two-wire temperature and resistive sensors
4. 21Hall-effect cam and crank sensors
5. 22Inductive sensors and AC signals
6. 23Pressure sensors — MAP, rail and A/C
7. 24Temperature sensors in real diagnosis
8. 25Position sensors and plausibility
9. 26Testing actuators: motors, solenoids and valves