Mass Air Flow Sensor DDE 5.0

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

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_HFM, supply voltage 5 V
  
• M_HFM, ground
  

Depending on the mass of fresh air drawn in, the mass air flow sensor returns a measurement voltage via the A_HFM signal to the DDE control unit. This measurement voltage is converted into air mass with the units mg/stroke/cylinder.

Troubleshooting

The air mass-flow meter is monitored for the following faults:

• 3FB0, Air mass flow too high or signal short cicuit to B+
  
• 3FB1, Air mass flow too low or signal short cicuit to B-
  
• 3FC0, Signal deviation too great at idling speed
  
• 3FD0, Signal deviation too great under load
  

The fault codes 3FC0 and 3FD0 are detected by air mass-flow meter calibration. See service function "Air mass flow meter calibration".

Consequence:

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