I. Identification of the installation location of the intake air temperature sensor
Intake air temperature sensors are typically mounted on the intake hose after the air filter or on the air flow sensor. On some turbocharged engines, they are integrated with the boost pressure sensor and mounted on the boost intake manifold behind the turbocharger, as shown in the figure below. Some engines also have one air flow sensor and one on the resonant cavity to improve the accuracy of fuel injection control.
1—Fastening screw; 2—Intake air temperature sensor
II. Function of the Intake Air Temperature Sensor
The function of the intake air temperature sensor is to measure the temperature of the gas entering the intake manifold. In a volumetric flow intake system, the electronic control unit (ECU) adjusts the fuel injection quantity based on the intake air temperature to obtain the optimal air-fuel ratio.
III. Working Principle of Intake Air Temperature Sensor
The structure of the intake air temperature sensor is shown in the figure below. It mainly consists of a plastic shell, a waterproof socket, a gasket, and a thermistor.
The intake air temperature sensor uses a thermistor with a negative temperature coefficient as the detection element. To accurately measure the intake air temperature, it is usually protected by a plastic housing to prevent the temperature of the installation part from affecting the working accuracy of the sensor.
IV. Typical Vehicle Series Circuit Connections
The diagram below shows the intake air temperature sensor circuit connection for the turbocharged engine in the new Cruze. The intake air temperature sensor is integrated with the turbocharger sensor and mounted on the intake manifold behind the turbocharger. The engine control unit (ECU) provides a 5V reference voltage to terminal #3 of the sensor, while terminal #1 of the sensor is grounded internally through the ECU.
V. Testing Methods
A malfunctioning intake air temperature sensor can cause an excessively rich or lean air-fuel mixture, leading to poor combustion and unstable operation. In this case, the intake air temperature sensor should be checked. The testing method is as follows:
Method 1: Individual Detection
01. Turn off the ignition switch, disconnect the intake air temperature sensor wiring harness connector, and remove the intake air temperature sensor.
02. Cool the intake air temperature sensor with refrigerant or compressed air, or heat the sensor by immersing it in water.
03. Use a multimeter in resistance mode to measure the resistance between the two terminals of the sensor. The resistance value should change with temperature in a manner consistent with the characteristic curve shown in the figure below.
Method 2: Online testing method (taking the new Cruze engine circuit mentioned above as an example)
01. Disconnect the sensor connector, turn on the ignition switch, and measure the voltage between terminal #3 on the connector and ground. It should be 5V. If there is no voltage, check the voltage between terminal #34 on the ECU connector and ground. If the voltage here is 5V, it indicates an open circuit between the ECU and the sensor; if there is no 5V voltage, the ECU is faulty.
02. Reinsert the plug, start the engine, and measure the voltage between sensor #3 terminal and ground at different temperatures. It should vary between 0.5 and 4V (slight differences may occur depending on the vehicle model, but the general pattern of variation is the same).
If the measured value does not match the specified value, it indicates that the intake air temperature sensor is faulty or damaged and should be replaced with a new one.
Typical vehicle series inspection examples
Example 1. Toyota vehicle intake air temperature sensor detection
In the Toyota Camry, the intake air temperature sensor C2 outputs an intake air temperature signal at terminal 1, and terminal 2 of C2 is grounded. A 5V voltage is supplied to the IAT sensor via the ECM's THA terminal through a resistor R. Resistor R and the IAT sensor are connected in series. When the resistance value of the IAT sensor changes, the voltage across terminal THA also changes. Based on this signal, the ECM increases the fuel injection quantity to improve the engine's performance when operating cold, as shown in the diagram below.
To check the intake air temperature sensor, measure the resistance between its terminals. At 20°C, the resistance should be 2.21–2.69 kΩ, and at 80°C, it should be 0.322 kΩ. If the resistance value is abnormal, the intake air temperature sensor should be replaced.
When the ECU detects fault code "0110/24 (Intake air temperature sensor circuit fault)," the following aspects should be checked:
◆Check the continuity of the sensor circuit wires to check for short circuits or open circuits.
◆The sensor itself can be checked by measuring the resistance of the intake air temperature sensor.
◆Whether the ECU is faulty or not.
2. Nissan vehicle intake air temperature sensor detection
In Nissan Livina vehicles, the air intake temperature sensor is integrated into a mass airflow sensor. The sensor detects the air intake temperature and converts it into an ECM signal.
This temperature sensor unit utilizes a thermostat that is sensitive to temperature changes. The resistance of this thermostat decreases as the temperature increases.
The reference values measured between ECM port 46 (intake air temperature sensor) and ground under different conditions are shown in the table below.
