Information on diagnostics

Air mass sensor with frequency output:

Testing and test values

How do you check digital air mass sensors? And what are the reasons why measuring air mass sensors with a multimeter may not work? 


Product: Air mass sensor

Models with 1.6 l diesel engine:
CITROEN Berlingo, C2, C3, C4, C5, Jumpy, Xsara Picasso (HDi)
FORD Fiesta, Focus, Fusion (TDCi)
PEUGEOT Expert, Partner, 1007, 206, 207, 307, 308, 407 (HDi)

Pierburg No.: 7.28342.06.0
Replacement for: 7.28342.04.0

O.E. No.*: 9650010780; 1232096; 1255117; 3M5A12B579BA; 3M5A12B579BB; Y60113215; 1920GV; 30774680

* The refence numbers given are for comparison purposes only and must not be used on invoices to the consumer.

Potential complaints:

  • Black smoke
  • Lack of power
  • Limp home function
  • Fault code P0100, P0101, P0102, P0103, P0104

These complaints can indicate a defective air mass sensor.

With this air mass sensor, the measured air mass fl ow rate is output as a frequency modulated rectangular signal. Therefore, an oscilloscope or a multimeter with frequency measuring range is required for testing.

An integrated temperature sensor records the intake air temperature. It can be measured as an electrical resistance with a standard Ohm meter or multimeter.

  1. Temperature resistance
  2. Earth
  3. (Not assigned)
  4. Supply voltage (12 V)
  5. Frequency output

Testing the supply voltage

Oscilloscope or corresponding function on an engine tester or multimeter

  • Disconnect the plug from the air mass sensor.
  • Connect multimeter or oscilloscope to pin 4 and pin 2 of the connecting cable ("Volt" measuring range).
  • Turn on the ignition.
    Setpoint value: On-board voltage (> 11 V)

Testing the temperature sensor

Multimeter or engine tester, thermometer, suitable equipment for generating heat, e.g. hot air gun.

  • Use a motor tester to test the actual intake air temperature values stored in the engine control unit.
    Setpoint value: Ambient air temperature


  • Disconnect the plug from the air mass sensor.
  • Connect the multimeter to pin 1 and earth (2) on the air mass sensor (“Resistance” measuring range).
  • Use a hot air gun and the thermometer to set various testing points.

0 °C - 5846 Ω / 25 °C - 2000 Ω / 40 °C - 1128 Ω / 60 °C -  564 Ω / 120 °C - 103 Ω

Testing the air mass flow rate

Oscilloscope or corresponding function on an engine tester

  • Air mass sensor can remain installed. Plug must remain connected.

As no method available in the workshop for determining the actual air mass passing through as a reference, the measured value with the engine stopped, i.e. air mass = 0, is used as a reference variable.

  • Turn on the ignition. Do not start the engine.
  • Measure the frequency between pin 2 and pin 5.
    Setpoint value: 5000 ±10 Hz
  • The signal voltage from the sensor must be around 12 V. In the oscilloscope image, this is the highest value of the rectangular signal.
  • Start the engine.
  • Press the gas pedal.
  • The frequency must now fall, i.e. the curve in the oscilloscope is extended further.

On some engine testers that have an integrated oscilloscope, it is possible to display a reference signal. The reference signal shows the voltage curve when idle. The two curves must be approximately congruent when idle.

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