The purpose of this test is to evaluate a hot film Air Flow Meter’s (AFM) voltage output with a turbo diesel engine during engine idle, acceleration, and over-run conditions.
This known good waveform has the following characteristics:
Air flow meters measure the quantity of filtered air entering an engine. Typically, Engine Control Modules (ECM) use these meters as the primary engine load sensor.
Hot film, or wire, air flow meters have a heated element located within the intake air flow. The voltage, and hence current, through the heated element’s 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 element’s temperature constant. Therefore, the heating 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.
The testing procedure and operating characteristics of hot wire and hot film air flow meters are the same.
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 smoke limitation value, leading to poor performance and/or incomplete combustion with excessive black smoke from the exhaust.
Selection of component related Diagnostic Trouble Codes (DTCs):
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.