Air flow meter (hot wire - turbo diesel)

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

This known good example waveform has the following characteristics:

With the engine at idle, the sensor voltage at around 1.75 V.

On the time scale between 1.25 s and 1.5 s you can see a rapid rise and slight levelling of the voltage. This is due to the initial influx of air as the throttle opens. The airflow then increases to maximum and the sensor 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.

Waveform Library

Go to the drop-down menu bar in the lower left of the Waveform Library window and search fo, Mass air flow sensor (MAF) hot wire .

Further guidance

Common rail diesel systems may be either turbocharged or normally aspirated. In both cases the airflow meter is located next to and after the air filter.

Intake airflow is monitored and data sent to the ECM.

The hot wire meter monitors the flow by 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 meter output terminal is directly proportional to air flow, increasing and decreasing with air flow.

Diagnostic trouble codes

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

GT009-4

Disclaimer
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

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • Large Dolphin/Gator Clips

    £10.00

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

    £47.00

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

    £179.00

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Guided test: Air flow meter (hot wire - turbo diesel)