Air Flow Meter/Sensor: Description and Operation

Mass Air Flow Sensor:

PURPOSE
The mass air flow sensor provides the ECM with continuous information regarding intake "air mass."

OPERATION
In operation, a "hot wire" is heated to a temperature of 180°C (356°F) above ambient temperature. This temperature is maintained regardless of outside air temperature. As air flows through the sensor, the current through the wire increases to maintain the 180°C (356°) temperature.

The Engine Control Module uses this current change as a signal of air mass entering the engine. The current is sensed by reading the voltage drop across the measuring resistor in the sensor. Changes in intake air temperature are corrected by the compensating resistor.

The hot wire is mounted in an inner sleeve for protection. Each end of the mass air flow sensor also has a protective screen attached to help prevent damage to the wire. To clean the heated wire of contamination, it is heated to 1000°C (1800°F) for approximately one second when the engine is switched off.

COMPONENTS
^ Heated Wire (Platinum)
^ Measuring Resistor
^ Compensating Resistor
^ Micro Processor