Diagnosing a Faulty Air Mass Meter

Air Mass Meters measure the air entering the engine and convert this into an electronic signal used by the Engine Control Unit (ECU) to determine engine load and calculate correct fueling and ignition timing. A small platinum sensor element is maintained at a constant temperature regardless of air flow. This is achieved by monitoring the resistance of the heated sensor, as more air flows, the sensor is cooled, and a feedback loop supplies more current to maintain the temperature. This current draw is then converted into a relative signal which is sent to the ECU. An additional ambient temperature sensor allows for correction of the signal due to intake air temperatures changes which have a huge impact on the output.

It is difficult to diagnose a faulty Air Mass Meter on symptoms alone, other faulty components such as Fuel Pump, Fuel Pressure Regulator and Vacuum System can all present similar symptoms, this is why it is important to troubleshoot the Air Mass Meter before replacing components.

On newer vehicle models, the car computer can produce precise diagnostic trouble codes (DTCs) that will pinpoint the cause of the problem.

Symptoms of faulty AMM:

• Decrease in engine power
• Engine vibration (poor idling)
• Hesitation or stalling under acceleration
• Lower fuel economy
• Engine surge whilst idling
• Other drivability problems
• Diagnostic fault codes

Troubleshooting:

• Locate the Air Mass Meter, usually between the air filter housing and throttle body. Usually a small block or cylindrical system mounted as part of the air duct. On certain models the AMM will be situated inside the filter housing
• The majority of AMM’s can be tested using a voltmeter, with an output between 0-5V. Upon ignition, the voltage will rise to the level for idle air flow, followed by gradual acceleration where you should see the voltage rise as the engine rev count increases. This reading will fall again with the rev count back to idle.
• When working correctly, you should see a smooth voltage change without jumps or hesitation. If the voltage remains constant, or doesn’t move with the engine revs, this indicates a fault with the AMM.
• Modern digital AMM cannot be easily tested with a voltmeter and require the use of an oscilloscope to test on vehicle. Digital sensors have become more common on modern vehicles due to their faster reaction times and improved accuracy. Rather than testing the voltage, a waveform is analysed to determine whether the sensor is working correctly.

Why Choose SMP Europe’s Platinum Sensor Element?

• Can be expected to provide 100,000km of life
• Exceeds OE testing outputs for road, air flow and high temp. degradation
• Corrosion resistant, prolonging the lifespan of the AMM
• Low cost aftermarket equivalents drift from tolerance by up to 10% by 10,000km
• Unreliable tolerances in low cost parts will increase the likelihood of recurring warning lights and fault codes

SMP Europe’s range of Air Mass Meters are available in Intermotor, Lucas, Lemark and FuelParts brands.