Resistance parameter: R25=5KΩ±1% B25/50=3950K±1% Operating temperature: -40 to +130℃ Withstand voltage test: 1000V AC 0.5mA 1Sec Insulation resistance: 500VDC 100MΩ Response time: ≤5s Operating voltage: 5±0.1VDC Working current: ≤0.5mA 1. Core Working Principle The internal sensitive element is an NTC Negative Temperature Coefficient Thermistor (universal type for vehicles): Low coolant temperature → High thermistor resistance High coolant temperature → Sharply reduced resistance ECU outputs a stable 5V reference voltage to the sensor, calculates coolant temperature by sampling voltage changes, and executes corresponding engine control logic. Typical resistance reference: 20℃ ≈ 2.5kΩ 90℃ (normal working temp) ≈ 300Ω 2. Main Structure Sensing core: NTC thermistor chip Heat-conductive brass metal probe (directly contact coolant) Sealing rubber ring (anti-coolant leakage) Threaded mounting body (standard threads: 1/8NPT, 14mm, 16mm, 17mm) Plastic electrical connector (2-pin / 3-pin plug) 3. Installation Position Main installation: Thermostat housing (coolant outlet of cylinder head) Alternative positions: Engine cylinder block water jacket, radiator upper pipeline Dual-sensor design (some old cars): One for ECU control, one independent sender for dashboard temperature gauge 4. Key Functions ① Engine fuel & ignition control Cold start: Low-temperature signal → ECU increases fuel injection volume, delays ignition timing to enrich mixture, avoid stalling & rough idle Warm engine: Normal temp signal → Reduce fuel supply, optimize ignition advance to cut fuel consumption & exhaust emissions ② Cooling fan automatic control When coolant exceeds threshold temperature, ECU activates radiator cooling fan to prevent engine overheating; reduce fan speed when cooling down. ③ Dashboard temperature display Transmit temperature data to the vehicle instrument water temperature gauge for driver visual monitoring. ④ Auxiliary system linkage Automatic transmission: Adjust shift logic & torque converter lock-up Car heater: Control warm air output EGR exhaust recirculation valve: Adjust opening timing according to engine temperature 5. Common Fault Symptoms Difficult cold start, severe engine jitter when cold Sharply increased fuel consumption, black exhaust smoke Water temperature gauge reading abnormal (always cold / always overheat alarm) Radiator fan keeps running continuously or never turns on ECU triggers engine fault code, enters power-limit protection mode Main Failure Causes Aging & resistance drift of internal NTC thermistor Connector oxidation, wire breakage / short circuit Seal failure, coolant infiltrates and corrodes internal components 6. Two Main Types ECU Control ECT Sensor (2-pin) Standard mainstream type, transmits precise temperature signal to engine computer, most passenger cars adopt this. Gauge Sender (Single-pin) Old mechanical instrument dedicated sensor, only drives dashboard temperature pointer without participating in engine fuel control. 7. Application Range Passenger cars, commercial vehicles, motorcycles Engineering machinery, generators, marine engines Modified racing vehicles with independent water temp gauge systems