The air flow sensor converts the sucked air into an electrical signal and sends it to the electronic control unit (ECU) as one of the basic signals to determine the fuel injection. According to different measuring principles, it can be divided into four types: rotating vane air flow sensor (Toyota PREVIA station wagon), Carmen vortex air flow sensor (Toyota Lexus LS400 car), dedicated air flow sensor (VG30E engine for Nissan Maxima and Volvo B230F engine for domestic Tianjin Sanfeng bus TJ6481AQ4) and hot film air flow sensor. The first two are volume flow type, and the last two are mass flow type. At present, there are mainly two kinds of air flow sensors: dedicated line air flow sensor and hot film air flow sensor.

1. The failure of the computer power cord will make the performance of the automobile engine worse and the economy lower, so the computer power cord should be checked first before the replacement of the automobile computer. (The power cord should include the ground wire to be considered as a complete power cord).

 2. If the voltage signal of the oxygen sensor is higher than the standard value, it may be that the sensor is polluted, and in many cases it will make the air-fuel ratio rich.

3. If the voltage signal of the oxygen sensor is lower than the standard value, it may be that the sensor is out of order, which will lead to the lean air-fuel ratio of the engine.

4, when checking the oxygen sensor must use digital multimeter, or oscilloscope.

 5. If the heater of oxygen sensor is faulty, it may prolong the open-loop working time of the engine and increase the fuel consumption.

6. The engine coolant temperature sensor can check its performance with a digital meter or an analog meter.

7. In the ect circuit of some computers, an internal resistor will be controlled at a certain temperature of the engine to change the voltage on the sensor. If the voltage at this time is abnormal during the measurement, it does not mean that the sensor is faulty.

8. Testing engine coolant temperature sensor and air temperature sensor can use exactly the same operation procedure, but the only thing to note is that their temperature change curves are different, so there will be no same voltage signal at the same temperature.

9. When the throttle valve is open and the voltage signal of the throttle position sensor is checked, the stability of the sensor can be checked by vibration with appropriate force. This method is very effective for some circuit virtual connection faults.

10. Many four-wire throttle position sensors include an idle position switch, which is used to provide the engine control unit with the working state information of the engine when the throttle is in the idle position.