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Switches & Sensors

Air Mass Sensor Troubleshooting

Troubleshooting

Clogged or defective air mass sensors will send faulty signals, or no signals at all. The symptoms are almost directly apparent as the vehicle may emit black smoke, suffer from a lack of power, or switch into the limp home function. Incorrect input signals from a defective air mass sensor can also cause the engine control unit to actuate other components incorrectly. For this reason, error messages such as "mixture control too lean/too rich" or "EGR flow rate too high/too low" may also indicate a defective air mass sensor.

One factor is however of great importance when troubleshooting:

Although air mass sensors are monitored by the on-board diagnostics system ("OBD"), they may not necessarily be the actual cause of the failure or fault.

 

 

 

Left: Air mass sensor in good condition with sensor element intact

 

 

 

 

 

 

Left: Air mass sensor in bad/defective condition with sensor element no longer intact

 

 

 

If the air mass sensor fails, the cause is often elsewhere in the system. Almost all air mass sensors submitted to Pierburg for warranty claims are full of oil or dirt or look "sandblasted". These symptoms indicate the possible true causes:

  • In the event of leaks in the intake air system, dirt particles can enter with the intake air which then hit the air mass sensor at high speed and destroy the sensitive sensor element.
  • Excessive oil mist from the crankcase ventilation can result in oil reaching the sensor.
  • Splash water, (for example, during heavy rain) can reach the clean air side via the air filter and damage or foul the sensor. Salt water, (for example, from road salt and sleet) intensifies this effect.
  • Oil particles from oil-wetted sports air filters can damage or soil the sensor.
  • Faults during servicing, for example, lack of cleanliness when replacing the air filter and the use of incorrect or inferior quality air filters, may be the cause of the intake of dirt and subsequent damage to the air mass sensor.
  • Other causes, such as defective exhaust gas recirculation or tank ventilation valves, leaks in the intake air system, clogged air filters or damage to the turbocharger, for instance caused by an incorrectly calibrated wastegate valve, can be potential reasons for an intact air mass sensor sending a faulty signal.

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