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.
Connection for diagnostic work will vary dependent on application.
Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.
General connection advice
PicoScope offers a range of options within the test kits.
Dependent on difficulty of access, choose from:
Testing sensors and actuators (to include relevant circuit/connectors):
This known good waveform has the following characteristics:
With the engine idling, the initial voltage is around 0.5 V.
When the accelerator pedal is rapidly and fully depressed, the voltage rises rapidly to almost 4.0 V, then falls to around 2.5 V. This initial voltage peak is due to the inrush of filtered air into the manifold when the throttle becomes fully open.
When the manifold is filled and its air pressure is equal to the ambient air pressure, the subsequent airflow is dependent on the engine speed. Therefore, as the engine speed increases to its peak, the voltage rises to around 4 V.
When the accelerator pedal is released and the throttle closes, the air intake and signal voltage drop rapidly.
As the engine overruns and its speed drops, the sensor voltage gradually reduces as the engine returns to its idle state. Some engine control modules will maintain or even increase airflow in this phase as an anti-stall feature.
The waveform hash is due to fluctuations caused by engine induction pulses.
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 poor performance, incomplete combustion events and other fuel trim or mixture related faults.
Note: 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):
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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