Mass Air Flow/Inlet Air Temperature Sensor (MAF/AT)

Mass Air Flow/inlet Air Temperature Sensor (MAF/IAT)





The air flow meter is located in the clean air duct immediately after the air filter box.

The air mass flow is determined by the cooling effect of intake air passing over a "hot film" element contained within the device. The higher the air flow the greater the cooling effect and the lower the electrical resistance of the "hot film" element. The ECM (engine control module) then uses this signal from the Mass Air Flow meter to calculate the air mass flowing into the engine.

The measured air mass flow is used in determining the fuel quantity to be injected in order to maintain the stoichiometric air/fuel mixture required for correct operation of the engine and exhaust catalysts. Should the device fail there is a software backup strategy that will be evoked once a fault has been diagnosed.

The following symptoms may be observed if the sensor fails:
^ During driving the engine RPM might dip, before recovering.
^ Difficulty in starting or start-stall.
^ Poor throttle response/engine performance.
^ Lambda control and idle speed control halted.
^ Emissions incorrect.
^ AFM signal offset

The IAT (intake air temperature) sensor is integrated into the MAF (mass air flow) sensor. It is a temperature dependent resistor (thermistor), i.e. the resistance of the sensor varies with temperature. This thermistor is a NTC (negative temperature coefficient) type element meaning that the sensor resistance decreases as the sensor temperature increases. The sensor forms part of a voltage divider chain with an additional resistor in the ECM (engine control module). The voltage from this sensor changes as the sensor resistance changes, thus relating the air temperature to the voltage measured by the ECM (engine control module).

The ECM (engine control module) stores a 25 Degrees Celsius default value for air temperature in the event of a sensor failure.