Air mass sensor with frequency output:

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.

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)

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

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.