Sensors and actuators in the induction system – faults and their effect


1. Mass air flow meter

General points

The mass air flow meter has the task of determining the air mass supplied to the engine. It comprises a tube-shaped housing with flow rectifier, sensor protection and sensor module screwed to the outside. It is mounted between the air filter housing and the throttle blade.

Effects of failure

A failed mass air flow meter can become noticeable as follows:

  •  The engine stops or the engine management control unitstarts to work in emergency running mode
  •  Loss of power
  •  Engine warning light comes on

Reasons for failure of the mass air flow meter can be

  •  Contact fault at the electrical connections
  •  Damaged measuring elements
  •  Mechanical damage (vibration, accident)
  •  Detachment of measuring elements(leaving the measuring framework)


  •  Read out faults stored in the engine management control unit
  •  Visual inspection of the plug-type connection, the cabling,the housing and sensor element
  •  Check the supply voltages and output signals using amultimeter or oscilloscope

2. Throttle blade

General points

Throttle blades are installed between the induction bridge and load sensor. Throttle blades control the air flow sucked in by the engine. The mixing ratio of fuel and air is changed by the throttle blade’s opening angle.

A distinction is made between the following throttle blade parts
1. Mechanical throttle blades

Actuated through the accelerator pedal via rods or Bowden cable

2. Electromotive throttle blades

Triggered through Bowden cable and control unit

3. Electronic throttle blades

Regulated and controlled through the control unit

Effects of failure

  • Loss of power
  • Misfiring during acceleration
  • Vehicle goes into emergency running mode Fluctuating idling speed
  • Engine warning light comes on

Causes of failure are

  • Soiling through oil carbon deposits
  • Mechanical blockage through foreign particles Defective actuator motor
  • Defective potentiometer


  •  Read out fault store
  •  Check the supply voltages and signals using amultimeter and oscilloscope
  •  Visual inspection of the cabling and mechanical assemblies

3. Induction pipe pressure sensor

General points

The induction pipe pressure sensor has the task of measuring the negative pressure in the induction pipe, downstream from the throttle blade. Induction pipe pressure sensors can be connected directly to the induction pipe by a hose or be installed directly in the induction pipe.

Effects of failure

A fault in the induction pipe pressure sensor can become noticeable as follows:

  • Great loss of power
  • Misfiring during acceleration
  • Fluctuating idling speed
  • Engine warning light comes on

Typical causes of failure are

  •  Damaged measuring elements
  •  Internal short-circuits
  •  No supply voltage, earth connection
  •  Soiled vacuum connection, torn or damaged vacuum pipe


  •  Check sensor for damage
  •  Read out fault store
  • Check vacuum connection, connection plug and cabling



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