The purpose of this test is to evaluate the voltage output and response time of the Air Flow Meter (AFM) during engine idle, Wide Open Throttle (WOT) and over-run conditions.
This known good waveform has the following characteristics:
Air flow meters measure the quantity of filtered air entering an engine. As such, they are used by the Engine Control Module (ECM) as the primary engine load sensor.
Hot wire air flow meters have a heated wire element located within the intake air flow. The voltage, and hence current, through the hot-wire circuit is varied to keep it at a fixed, hot, temperature. As the air flow increases, its cooling effect increases, and the greater the voltage required to keep the wire temperature constant. Therefore, the hot-wire circuit voltage indicates the air flow to the ECM. The sensor element and air flow meter body form a calibrated unit and are not interchangeable.
Due to their position within the air intake tract, air flow meters can be prone to contamination, e.g. if a vehicle is poorly serviced with ineffectual air filters, or if it has other intake, crankcase breather, or exhaust recirculation faults. In such cases, the meter’s readings can be erroneous, causing the ECM to incorrectly calculate the air-fuel mixture, possibly leading to the following symptoms:
Air flow meter circuits (including the power, ground and signal circuits) are also susceptible to common electrical circuit faults, such as:
Some manufacturers use hot film air flow meters. The testing procedure and operating characteristics are the same as the hot wire type.
Selection of component-related Diagnostic Trouble Codes (DTCs):
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