Air Flow Meter/Sensor: Testing and Inspection

Diagnosis of Air Mass Meter

The output voltage of the air mass meter is a measure of air mass flow. The diagnostic routine compares the mass flow measured by the air mass meter with a calculated mass flow, derived from engine speed and throttle valve position.

If the measured mass flow from the air mass meter is greater than a threshold value from the characteristic map, a fault is detected. In case of a throttle valve fault the characteristic map is addressed with the maximum throttle valve angle. In this case the uppermost threshold values will be taken for comparison.

If the measured air mass flow from the air mass meter is lower than a threshold value from the characteristic map multiplied with a value from the a characteristic line, the table value depends on ambient pressure, a fault is detected. In case of a throttle valve fault, the characteristic map is addressed with the minimum throttle valve angle.

In case of an ambient pressure sensor fault, the characteristic map is multiplied with the minimum ambient pressure value. In this case the lowest threshold value will be taken for comparison.

The diagnostic routine will be executed if end-of-start is reached and after a debounce time.