Conventional fault performance of the eight sensors of the car!

The function of each sensor and the way of failure expression

Air flow sensor

Currently, hot-wire air flow sensors and hot-film air flow sensors are mainly used, which are generally installed between the air filter and the throttle.

Function: Measure the air intake of the engine and input the signal into ECU as the main control signal for fuel injection and ignition control.

Failure mode: After the air flow device fails, the car computer (ECU) cannot detect the real intake of air, resulting in an imbalance of the mixture, resulting in unstable engine idling, weak driving and black smoke, and sometimes shifting gears Flame out

Intake pressure sensor

The intake air pressure sensor is abbreviated as MAP sub-resistance intake air pressure sensor and capacitive intake air pressure sensor. It is installed on the intake manifold and is usually integrated with the intake air temperature sensor.

Function: Detect the absolute pressure of the intake manifold, then convert it into a voltage signal and send it to the ECU. The ECU controls the basic fuel injection volume according to the signal voltage.

Failure mode: The fuel injection quantity cannot be controlled normally, causing the mixture to be too thick or too lean, causing the engine to run abnormally, and the idle speed will also be unstable, often stalling, fuel consumption soaring or even unable to start when it is severe.

Throttle position sensor

The throttle position sensor is divided into a switch contact type throttle position sensor, a linear variable resistance type throttle position sensor, and a comprehensive throttle position sensor. The throttle position sensor is installed on the throttle to detect the opening of the throttle.

Function: The main function of the throttle sensor is to feed back the opening of the throttle to control the fuel injection amount during acceleration.

Failure mode: abnormal engine idling (such as excessive or low idling, unstable idling, easy stalling at idling speed) or abnormal engine acceleration (engine shaking during acceleration, slow acceleration response, etc.), sometimes causing the engine to run Phenomenon such as intermittent jitter occurs.

Camshaft position sensor

The camshaft position sensor is used to detect the angular position of the camshaft, and the engine control module (ECU) uses this signal to determine the cylinder sequence of the engine.

Function: detect the position of the camshaft, determine the top dead center of a cylinder compression stroke, and control sequential fuel injection and ignition

Failure mode: When the camshaft position sensor fails, the output power of the engine will decrease. There will be problems such as the ignition failure, the gas pedal is difficult to add up, the car will tremble, and the fault light will always be on, and the fire will be turned off when the car is hot.

Crankshaft position sensor

The crankshaft position sensor (CKP) is one of the most important sensors in the engine centralized control system, and it is an indispensable signal source for confirming the crankshaft angle position and engine speed.

Function: The engine control module (ECU) uses this signal to control the fuel injection volume, fuel injection timing, ignition timing (ignition advance angle), ignition coil charging closing angle, idling speed and the operation of the electric gasoline pump.

Failure mode: The crankshaft position sensor is broken, and the crankshaft rotation angle cannot be confirmed. The engine computer cannot receive the signal from the crankshaft position sensor. In order to protect the engine from ignition or fuel injection, the sign of the car is that there is no high voltage electricity. , No fuel injection, no driving.

Oxygen Sensor

Function: The fundamental function of the oxygen sensor is to detect the oxygen concentration in the exhaust gas, and then the ECU (engine system control computer) will use the oxygen concentration signal provided by the oxygen sensor to determine the engine's combustion status (pre-oxygen) or the working efficiency of the catalyst (Post oxygen). There are zirconia type and titanium oxide type.

Failure mode: If the oxygen sensor fails, the engine performance is poor, the lambda adjustment is fixed, the idle speed is unstable, the emission value is abnormal, the fuel consumption increases, and the spark plug is deposited. Oxygen sensor poisoning is a fault that often occurs and is difficult to prevent, especially in cars that often use leaded gasoline.

Water temperature sensor

The water temperature sensor is actually a semiconductor thermistor, the lower the temperature, the greater the resistance; conversely, the smaller the resistance, it is installed on the water jacket of the engine block or cylinder head and is in direct contact with the cooling water.

Function: Used to detect the temperature of engine cooling water. The electronic control unit corrects the fuel injection and ignition timing according to the water temperature signal, and installs a water temperature warning light on the instrument panel.

Failure mode: When the water temperature sensor fails (usually poor contact, short circuit, open circuit, but mostly poor contact), the phenomenon is ON, the engine fault light is always on, the water temperature always displays the maximum value of 120 degrees Celsius, the engine Torque limited and weak, the detected fault code is P003D. If the water temperature sensor fails, the car will experience difficulty in cold start, abnormal fuel supply, weak acceleration, and backfire during rapid acceleration.

Knock sensor

Function: The knock sensor is used to detect whether knock occurs during the combustion process of the engine, and send the knock signal to the engine control computer as an important reference signal for correcting the ignition advance angle.

Failure mode: When the knock sensor fails, the engine will deflagrate, the ignition timing will be inaccurate, high fuel consumption, power reduction, start-up difficulty, and rough engine operation.