Evaluation of road speed signal

The road speed signal is required by the DME control unit in order to perform several functions:

• Speed limiting function:

  Once the maximum road speed has been reached, the fuel injection and ignition are adjusted. If required, individual ignition and injection signals are suppressed. A "soft" speed limiting function is thus carried out.

• Control of A/C compressor:

  When the air-conditioning system is switched on, the A/C compressor is switched off during full-load acceleration, provided that: the car's road speed is less than 13 km/h.

• Idle speed control:

  If the car's road speed is 0 km/h, the idle speed is adjusted (depends on A/C compressor ON, selected drive position for automatic transmission, light ON).

• Poor-road-surface detection:

  At low road speeds, the check for smooth engine operation is switched off.