Mass Air Flow Sensor DDE 4.1

The air mass drawn in by the engine is measured by two mass air flow sensors in the intake tract of the DDE 4.1. The mass air flow sensors are identical components.

The air mass serves as a measurement variable for following functions:

• Exhaust gas recirculation
  
• Calculating limitation volume
  

Function

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

• U_HR, battery voltage
  
• U_HFM1, U_HFM2 supply voltage 5 V
  
• M_HFM1, M_HFM2 ground
  

Depending on the mass of fresh air drawn in, the mass air flow sensors return measurement voltages to the DDE control unit in the form of A_HFM1, A_HFM2 signals. The measurement voltages are converted into air mass with the unit of measure being mg/stroke/cylinder.

Troubleshooting

If a defect is detected in a mass air flow sensor or in a supply line, fault code 0101 "mass air flow sensor 1" or 3605 "mass air flow sensor 1 or 2" is stored and the DDE control unit switches over to a substitute characteristic curve.

Consequence:

• Exhaust gas recirculation is deactivated
  
• Deactivation of boost pressure control
  
• Volume limitation to 32 mm^3/stroke/cylinder
  
• Output of a substitute value dependent on engine speed