The purpose of this test is to evaluate the voltage output and response time of the AFM during engine idle, 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 example has the following characteristics:
The inital idle voltage rises rapidly to almost 4.0 V, then falls to around 2.5 V. This initial peak and drop is due to the rapid influx of air at the instant the throttle opens.
The voltage then climbs to around 4 V with the throttle fully open you can then see the voltage drop as the throttle closes. This is followed by a gradual reduction as the engine returns to idle.
There are a number of control units that will maintain or even increase air flow in this phase as an anti-stall protocol.
The hash on the waveform is due to fluctuations caused by engine induction pulses.
The function of the Mass Air Flow (MAF) meter is to provide the Engine Control Module (ECM) with data relating to intake air flow and mass.
The Hot Wire Air Flow Meter has a number of advantages over the earlier Vane type meters in that it has very little restriction to air flow. The mass air flow is measured by the cooling effect of the incoming air on an electrically heated wire suspended in the air flow. The Hot Wire sensor will also respond to air density, increased density will increase this cooling effect. Vane type meters cannot do this and require a separate pressure sensor to determine mass.
The Hot wire meter is able to react very quickly to temperature changes in the wire by increasing current to heat up or reducing current to cool down. The system attempts to maintain a constant wire temperature of around 120°C. These current changes are therefore directly proportional to air mass flow.
The current flow changes are converted by the meter into a calibrated voltage signal which is sent to the ECM, which in turn changes fuel delivery to maintain efficiency.
The heated wire will suffer from a build-up of oxides on the surface. This is negated by the fact that the ECM will clean the wire after each engine run by increasing current for a short time to get the temperature up to around 1000°C.
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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