Car Water Temperature Sensor Plug (for Radiator Cooling Fan)

The water temperature sensor is the core component of the car cooling system. Its core component is the NTC thermistor, which is installed on the engine cylinder head or water channel. This component looks simple, but it is actually very critical to engine control. It will directly affect the ECU’s adjustment of the injection amount and ignition timing.

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The resistance of the thermistor inside the sensor will change with temperature: the lower the temperature, điện trở càng lớn, and the higher the temperature, the smaller the resistance. The ECU determines the water temperature by measuring this resistance change. 8 Supplementary Note: At 30°C, the resistance is usually between 1.4-1.9kΩ.

The installation position of the water temperature sensor varies greatly for different models: Corolla is on the right side of the cylinder block, Accord is on the front of the engine, and Focus is on the rear of the cylinder block. Modern models are more installed on the side of the cylinder head near the thermostat.

Common failure phenomena of water temperature sensors: difficult cold start, unstable idle speed, abnormal water temperature gauge, vân vân. The engine needs to increase the injection amount by 30% at low temperatures, and if the sensor fails, it cannot be compensated correctly.

There are five ways to detect water temperature sensors: multimeter resistance measurement, hot water test, data flow analysis, vân vân. Trong số đó, heating test with a multimeter is the most commonly used on-site detection method.

When replacing the water temperature sensor, the coolant must be drained first, otherwise it will cause air intake in the cooling system. Sau khi cài đặt, the sealing should also be checked to prevent coolant leakage.

0015422317 A0105422317 0025425917 0005423717 3455427417 Coolant Water Temperature Sensor Switch

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The following is a comprehensive description of the automotive water temperature sensor, which is organized in combination with technical principles, functional characteristics and troubleshooting points:

TÔI. Core structure and working principle

1. Thermistor characteristics
Using negative temperature coefficient (NTC) semiconductor materials, the resistance value decreases exponentially when the temperature rises (about 2.5kΩ at 20℃, and drops to 0.3kΩ at 80℃).
The resistance change is converted into an electrical signal (1.3-3.8V linear range) through a three-wire or four-wire circuit and transmitted to the engine control unit (ECU).

2. Signal output logic
The ECU calculates the water temperature in real time after receiving the voltage signal:
Low temperature conditions (-20oC): Increase the ignition advance angle by 8-12° and increase the injection amount (+30% cold start compensation).
High temperature conditions (100oC): Delay the ignition advance angle by 4-6° to prevent explosion.

Ii. Installation location and type

Ghi chú: Modern models mostly use a four-wire integrated sensor, which is fixed at the thermostat interface on the side of the cylinder head.

Iii. Detailed explanation of functions and effects
1. Engine control
Fuel correction: increase the injection concentration at low temperature and restore the reference injection amount at high temperature.
Idle speed adjustment: increase the speed to 1200-1500rpm at low temperature (through the idle speed control valve).
2. Cooling system management
When the water temperature is ≥95℃, the cooling fan is triggered to start (coordinated with the normally closed temperature control switch).
When the temperature is abnormally high (＞105℃), the fan high-speed operation mode is activated.
3. Instruments and diagnosis
The drive water temperature gauge displays the real-time temperature (lỗi <±15℃ is normal).
Output fault code (such as P0115/P0118) for the diagnostic instrument to read.

Iv. Fault manifestation and diagnosis
Common fault types

Diagnostic method
1. Resistance test
Remove the sensor and use a multimeter to measure the resistance between the terminals:
30℃ environment: normal resistance value 1.4-1.9kΩ.
80℃ hot water immersion: resistance should drop to 0.3–0.4kΩ (if unchanged, failure).

2. Data flow analysis
The diagnostic instrument reads the ECU data flow:
Normal value: 90–105℃ (driving).
Fault prompt: Display -40℃ (open circuit) or 130℃ unchanged (short circuit).

V.. Maintenance precautions
1. Replacement operation specifications
Drain the coolant before removing the sensor to avoid air intake in the cooling system.
Use sealant during installation, and control the torque to 8–12N•m (leakage prevention).
2. Model selection and matching
Resistance range: Need to match the original car’s 275–6500Ω resistance characteristics.
Interface type: Confirm the specifications such as M18×1.5 thread or ZM14 taper thread.
Warning: Sensor failure can cause fuel consumption to increase by more than 15% or permanent damage to the engine, and needs to be replaced in time.
mermaid Copy Code
graph TD
MỘT[Water temperature sensor failure] –> B{Detection steps}
B –> C[Multimeter resistance measurement]
B –> D[Diagnostic instrument reads data stream]
C –>|Abnormal resistance| E[Replace sensor]
D –>|Signal drift| E
C –>|Normal resistance| F[Check line grounding]
D –>|Normal signal| G[Check other systems]