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? 

Vehicles: CITROEN, FORD, PEUGEOT

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

Equipment:
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

Equipment:
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

Alternatively:

  • 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.

Examples:
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

Equipment:
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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