The purpose of this test is to check the output from a digital MAF sensor.
Connect two of the general BNC test leads together, coloured plug to coloured plug and black plug to black plug. With a back-pinning probe connected to the coloured plugs, probe the signal wire on the MAF sensor as shown in Figure 1. Connect a black clip to the two black plugs and clip it onto the vehicle's earth. Connect the two test leads to Channel A and Channel B on the scope.
Analogue MAF Sensors: Most Mass Air Flow (MAF) sensors have analogue outputs that typically vary from 0.5 V to 4.5 V (0 V or 5 V is an error condition). The output of these sensors does not, however, change linearly with air flow, and requires scaling and corrections to be applied by the ECU. Typical outputs from non-turbo engines are shown in the "Hot-Wire Air Flow Meter" and "Moving-Vane Air Flow Meter" topics.
Digital MAF Sensors: Some modern MAF sensors contain digital electronics so that the scaling and corrections can be made within the sensor, thus improving accuracy. Whilst you can see the digital output (Channel B in the example above) changing frequency with airflow, it is not easy to interpret the signal using a conventional oscilloscope. Fortunately, PicoScope has an option to measure frequency against time in the software (R6.4.28 onwards), allowing us to look at the same signal as the ECU. The example waveform shows this feature in use on a turbocharged diesel vehicle. The vertical scale on Channel A is frequency.
The frequency option is available beginning with the PicoScope 4000 Series of automotive scopes. It is an additional item in the AC/DC drop-down menu.
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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