Air-mass sensor M67

The air-mass sensors measure the fresh air mass drawn in by the engine in both intake channels.

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

• Exhaust gas recirculation
  
• Calculating limitation volume
  
• Equalisation controller
  

Function

The DDE control units supply the mass air flow sensors with voltage and ground as follows:

• U_HR, battery voltage
  
• M_HFM1/M_HFM2, earth
  

The intake air temperature sensors return the air mass values to the DDE control units via the signals T_HFM1/T_HFM2.

The signal of the air-mass sensors is a square-wave signal with the following values:

• Amplitude = 12 V
  
• Frequency = 1.2 - 14 kHz
  

The DDE control unit 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 turbo pressure control
  
• Volume limitation
  
• Output of a substitute value dependent on engine speed