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:
With the engine at idle, the waveform voltage varies between 1.5 and 2.0 V.
After the accelerator pedal is rapidly and fully depressed, the engine speed increases rapidly and the voltage rises to over 4 V.
After the accelerator pedal is released, the engine speed decreases as it overruns, causing the air-mass to reduce and the waveform voltage to rapidly decline.
With the engine approaching idle speed around 1200 rpm, an anti-stall function is activated, at around 3.5 s in the waveform, causing the air mass to decrease more gradually.
The waveform hash is caused by induction pulses as the engine runs.
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):
P00BC Mass or Volume Air Flow "A" Circuit Range/Performance - Air Flow Too Low
P00BD Mass or Volume Air Flow "A" Circuit Range/Performance - Air Flow Too High
P00BE Mass or Volume Air Flow "B" Circuit Range/Performance - Air Flow Too Low
P00BF Mass or Volume Air Flow "B" Circuit Range/Performance - Air Flow Too High
P0100 Mass or Volume Air Flow "A" Circuit Malfunction
P0101 Mass or Volume Air Flow "A" Circuit Range/Performance Problem
P0102 Mass or Volume Air Flow "A" Circuit Low Input
P0103 Mass or Volume Air Flow "A" Circuit High Input
P0104 Mass or Volume Air Flow "A" Circuit Intermittent
P010A Mass or Volume Air Flow "B" Circuit
P010B Mass or Volume Air Flow "B" Circuit Range/Performance
P010C Mass or Volume Air Flow "B" Circuit Low
P010D Mass or Volume Air Flow "B" Circuit High
P010E Mass or Volume Air Flow "B" Circuit Intermittent/Erratic
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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