Mass Air Flow And Temperature Sensor

WARNING: This page is about a different car, the 2018 Land Rover Discovery Sport. However, it is still accessible from the selected car via links, so may be relevant.

The air filter housing is located in the left front corner of the engine compartment. The air outlet connection of the air filter housing incorporates a Mass Air Flow and Temperature (MAFT) sensor. The MAFT sensor is secured with two screws and measures the air entering the clean air duct to the turbocharger.

The MAFT sensor receives a 5 V power supply from the Powertrain Control Module (PCM). Three further connections provide signal feedback to the PCM for air mass, temperature and ground.

The MAFT sensor works on the hot film principle. Output is a frequency based signal which equates to the mass of air being drawn into the engine.

The PCM checks the calculated air mass against the engine speed. If the calculated air mass is not plausible, the PCM uses a default air mass value. This default air mass value is derived from the average engine speed compared to a stored characteristic map. The air mass value will be corrected using values for charge air pressure, atmospheric pressure and air temperature.

The temperature of the air flow is measured with a Negative Temperature Coefficient (NTC) thermistor in the MAFT sensor. The NTC thermistor works on the principle of decreasing resistance in the sensor as the temperature of the intake air increases. The change in voltage is proportional to the temperature change of the intake air. Using the voltage output from the MAFT sensor, the PCM can correct the fueling map for intake air temperature. The correction is an important requirement because hot air contains less oxygen than cold air for any given volume.

The PCM uses the MAFT sensor output, signals from the other sensors. The information is stored in fueling maps to determine the precise fuel required by the engine.

If the MAFT sensor fails the PCM implements the default strategy based on engine speed.

In the event of a MAFT sensor signal failure, any of the following symptoms may be observed:

Difficult starting

Engine stalls after starting

Delayed engine response

Emission control inoperative

Engine idle speed fluctuation

Reduced engine performance.

If the temperature sensor of the MAFT sensor fails the PCM uses a default intake air temperature of -5°C (23°F).

In the event of a temperature sensor failure any of the following symptoms may be observed:

Over fueling

Engine idle speed fluctuation.