Airflow meter - diesel Bosch common rail

The purpose of this test is to evaluate the voltage output and response time of the Air Flow Meter during engine idle, WOT and over-run conditions. 

Connection guidance

Connection for diagnostic work will of course 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,

  1. Breakout leads.
  2. Back-pinning probes.

Testing Sensors and Actuators; (to include relevant circuit/connectors).

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use a vehicle circuit diagram to identify the Air Flow Meter (AFM) output signal terminal, at the control unit if access allows.
  2. Connect to Channel A of your PicoScope.
  3. Start the engine.
  4. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  5. Select GO or press the space bar to see live data.
  6. Carry out a Wide Open Throttle (WOT) test to capture your data.
  7. With your live waveform on screen select stop or press the spacebar to stop your capture.
  8. turn off the engine.
  9. use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

The example waveform shows an engine idle voltage of around 1.75 V. On the time scale between 1.25 s and 1.5 s you can see the initial rapid rise and slight levelling of the voltage. This is due to the initial influx of air as the throttle opens. The air flow then increases to maximum and the meter output records just under 4 V.

As the throttle closes the voltage falls. At a point around 3.5 s you can see a short levelling and then a more gradual decrease in voltage. This is an anti-stall feature and usually activates at around 1200 RPM.

The hash or oscillations in the waveform are caused by the induction pulses as the engine runs.

Waveform Library

There are 70 examples to be found in the Waveform Library.

Go to the drop-down menu bar in the lower left of the Waveform Library window and search for Mass Airflow Sensor.

Further guidance

Technical Information

The Bosch common rail diesel system may be either turbocharged or normally aspirated. In both cases the airflow sensor is located next to the air filter.

The airflow meter monitors the volume of air and supplies the ECM with the relevant data. It uses a conventional method of monitoring the flow by means of controlling the temperature of a heated platinum wire. The incoming air passes over the hot wire cooling it and altering the output voltage. The voltage at the AFM output terminal is directly proportional to air flow, increasing as the airflow increases.

Generic DTC’s MAF Sensor.

P0100 - MAF Sensor Circuit Insufficient Activity

P0101 - Mass Air Flow (MAF) Sensor Performance

P0102 - Mass Air Flow (MAF) Sensor Circuit Low Frequency

P0103 - Mass Air Flow (MAF) Sensor Circuit High Frequency

P0104 - Mass Air Flow Circuit Intermittent


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.

Suitable accessories

  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


  • Premium Test Lead: BNC to 4 mm, 3 m


  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)


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Guided test: Hot Wire (Turbo Diesel)