Air mass sensor with frequency output:

Testing and test values

Information on diagnostics

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

Introduction

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.

19029 — Mass fl ow rate sensor characteristic curve

19028 — Temperature sensor characteristic curve

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.

18958 — Signal when idle (depending on idle speed)

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.