Air-mass sensor M57TU

The mass air flow sensor measures the mass of fresh air drawn in by the engine.

The air mass serves as a measurement variable in the DDE control module for the following functions:

• Exhaust gas recirculation
  
• Calculating limitation volume
  

Function

The DDE control module supplies the mass air flow sensor with voltage and ground as follows:

• U_HR, battery voltage
  
• M_HFM, ground
  

The air-mass sensor returns the air mass value via the signal T_HFM to the DDE control module.

The signal is a square-wave signal with an amplitude of 5 V and frequency between 1.2 - 14 Hz. This frequency corresponds to a period duration of 0.8 - 0.07 ms.

The DDE control module uses the frequency of this signal to calculate the air mass value with the unit mg/stroke.

Troubleshooting

Fault reactions:

• Exhaust gas recirculation is deactivated
  
• Deactivation of charge-air pressure control
  
• Volume limitation
  
• Output of a substitute value dependent on engine speed