SMP Europe

Air Mass Meters (also known as: Mass Air Flow Sensor, MAF sensor, Hot Wire Air Flow Sensor, Hot Wire Sensor, Air Flow Meter) are a critical component of a vehicle’s fuel delivery system. These sensors precisely measure the air flow into the engine, and send a signal to the ECU to calculate the injected fuel quantity. In diesel engines they also help to control exhaust gas recirculation. Defective Air Mass Meters send incorrect information to the ECU, which then causes incorrect operation of other components.

Depending on the application, Air Mass Meters can consist of two main components; the tube or housing, and the sensor unit. These can be supplied as a complete unit or replacement insert. There are two main types of air mass meters: hot wire (older vehicles) and hot film (newer models). In hot wire systems, contaminants are burnt off as it heats up briefly after switching the engine off. Hot film systems do not have a burning off process. Both types of Air Mass Meter consist of a sensor element, and a small electrical resistance heater. The heater is used to warm up the sensor, which is cooled by the air flow into the engine. The unit’s internal electronics convert the change in temperature to calculate air mass, and send a signal to the ECU, which uses the information to calculate the correct amount of fuel to inject into the engine.

There are several potential causes of damage to Air Mass Meters:

  • Leakages in the intake air system can allow dirt to enter, hitting the Air Mass Meter at high speed in the air flow, causing damage to the delicate sensor element.
  • Excess oil mist from crankcase can contaminate the sensor
  • Servicing errors, such as dirty working environment, or using poor-quality air filters can also leads to dirt particle damage to sensor
  • Water damage, such as splash water, or salt water from road can damage or contaminate sensor components

Other factors that can cause an undamaged Air Mass Meter to provide incorrect signals:

  • Defective EGR Valves
  • Leakages in the air intake system
  • Blocked air filter
  • Damage to the turbocharger

Common OBD codes specific to Air Mass Meters

  • P0100 – Malfunction in the air mass or air flow meter circuit
  • P0101 – Problem with the measuring range or power unit of the air mass or air flow meter circuit
  • P0102 – Air mass or air flow meter circuit too small
  • P0103 – Air mass or air flow meter circuit too large
  • P0104 – Misfire in the air mass or air flow meter circuit

Common OBD codes for problems that can be caused by incorrect signals from Air Mass Meter

  • P0171 – Mixture control (bank 1) system too lean
  • P0172 – Mixture control (bank 1) system too rich
  • P0175 – Mixture control (bank 2) system too rich
  • P0401 – EGR System – insufficient flow rate
  • P0402 – EGR System – excessive flow rate

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


  • 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 and it should be replaced.
  • 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.
  • Warning: Do not connect or disconnect any plug-in connections with the ignition turned on as this can damage or destroy electronic components within the sensor unit.

SMP Europe Air Mass Meters

In conclusion, the air mass meter is a vital component of a vehicle’s fuel delivery system. SMP Europe has drawn upon over 50 year’s experience in the design and manufacture of Engine Management and Ignition components to be renowned as one of the leading manufacturers of aftermarket Air Mass Meters. We provide quality, dependable units, that meet OE performance standards, across one of the largest ranges available in the automotive aftermarket.

Designed and developed in the UK at our Centre of Engineering Excellence, in Nottingham, our Air Mass Meters utilise the latest technologies and materials. Prototypes must pass our stringent testing processes before entering development, exceeding OE specifications for Road, Air Flow and High Temperature. Sensors are wire bound to ensure durability, and all units are end of line tested on bespoke, in-house, built equipment to OE specification – then issues with a serialised test certificate for traceability and peace of mind.

Whilst many aftermarket alternatives contain basic electronic components, SMP Europe sensors include custom designed electronics, also developed in-house by our engineering team, giving them a proven record for high performance over a long service life. We use platinum sensor element technology, which is corrosion resistant, to prolong the life of the product, and keep it within tolerances for up to 100,000km.

  • 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

Our range of Air Mass Meters are available across all main brands, including Intermotor, Lemark and Lucas. For more information please speak to your dedicated sales representative, or get in touch with us now at