Mass Air Flow Sensor And Temperature Sensor
The air filter housing is located in the front left corner of the engine compartment. The air outlet connection of the air filter housing incorporates a MAFT sensor. The MAFT sensor is secured with 2 screws and measures the air entering the clean air duct to the turbocharger.
The MAFT sensor has a 4-pin connector. The 4-pin connector provides the following connections:
- A 5V power supply from the PCM .
- An air mass signal to the PCM .
- An air temperature signal to the PCM .
- A ground connection.
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 gets 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) sensor in the MAFT sensor. The NTC sensor 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 and the information 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.
- Idle speed control inoperative.
- 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
- Idle speed control inoperative.