Substitution For Missing Signals

The IFI control module (N3/7) replaces missing input signals with substitute values based on other signals available in order to maintain system function:

• Loose Connections
  
  Loose connections are stored if they occur several times in a certain time period. Therefore, they can appear only as a stored DTC and never as an actual DTC.
• Actual Value For Engine Coolant Temperature
  
  In case of an open or short circuit, the actual value is immediately replaced by a substitute value which is very close to the actual value. Therefore, a fault can not be recognized clearly. A readout of the fault is possible only via the DTC memory.
• Actual Value For Engine RPM
  
  The HHT display indicates the closed throttle (idle ) speed nominal value calculated by the control module on the left and the RPM actual value on the right.
• Actual Value For Injection Quantity
  
  The HHT display indicates injection quantity nominal value calculated by the control module on the left and the injection quantity actual value on the right.
• Actual Value For Intake Manifold Pressure
  
  The HHT, display indicates the intake manifold pressure nominal value calculated by the control module on the left and the intake manifold pressure actual value on the right.

The values should differ from each other only slightly. The permissible tolerances are presently unknown.

The substitute values may result in :

• Performance reduction; reduction of maximum engine RPM.
• Switching OFF anti-vibration control.
• EGR system malfunction.
• Cruise control malfunction.
• Intake MAP control malfunction.