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Mass air flow sensor/intake air temperature sensor

Mass air flow sensor/intake air temperature sensor


The task of the mass air flow sensor is to continually measure the air mass used by the engine while it is running and to measure the temperature of the incoming air. The sensor comprises two main parts, the connection pipe and the sensor.

The pins are connected as follows;


1. Temperature of incoming air

2. Power supply

3. Sensor ground

4. Power supply

5. Air mass voltage


Measurement is conducted in the following way. Some of the air flow through the mass air flow sensor passes a measuring plate. The surface of this plate is a thin diaphragm of semi-conductor type on which a heating element and a number of temperature sensors are fitted. The heating element is a resistor, which radiates heat when current passes through it. Together with the resistor, there is a temperature sensor that enables the heat in the heating element to be regulated exactly. The temperature of the heating element is dependent on the temperature of the incoming air.

There are two more temperature sensors on the diaphragm, one upstream and one downstream from the heating element seen from the direction of the airflow. If there is no air flowing past the diaphragm, the temperature will be the same across its entire surface. The two temperature sensors upstream and downstream from the heating element will then detect the same temperature.

When air starts to flow through the mass air flow sensor, the diaphragm upstream from the heating element will cool down, which the temperature sensor on the diaphragm will detect. The temperature of the diaphragm and the temperature sensor downstream from the heating element will be the same as before the airflow started.

By measuring the difference in temperature of the airflow between the two temperature sensors (upstream and downstream), the air mass can be calculated.

The direction of flow can also be determined by taking into account which of the temperature sensors is the warmest and the coldest respectively. All the necessary calculations are carried out in the mass air flow sensor.

The signal, which is available to the engine management control module, consists of the calculated air mass and the temperature of the incoming air.

Diagnostics, mass air flow sensor


If the input is short-circuited to B+, diagnostic trouble code P0100 will be generated.

If the input is short-circuited to ground, diagnostic trouble code P0104 will be generated.


System reaction to a fault

• As soon as the control module detects a fault, the substitute value 800 mg/combustion will be used.

• The control module activates the "fuel limitation on system fault" function, see .

• The reading on the diagnostic instrument for P0100 and P0104 is 800 mg/combustion.


Diagnostics, intake air temperature sensor

If the sensor input is short-circuited to B+, diagnostic trouble code P0110 will be generated.

If the sensor input is short-circuited to ground, diagnostic trouble code P0111 will be generated.