Multifunction steering wheel (MFL) signal to DDE 5.0

The multifunction steering wheel sends the signals for the cruise control system to the DDE control unit in the form of the FGRS signal.

MFL detection

So that the DDE knows whether a multifunction steering wheel is fitted, the MFL sends the DDE control unit a signal that consists of a single bit, the ”toggle bit”. That bit continuously changes its status from 0 to 1 and back again. That alternation of signal status (toggling) tells the DDE control unit that an MFL is fitted. Once the presence of the MFL has been detected, that information is permanently stored on the DDE control unit. However, the toggle bit continues to be transmitted by the MFL and is used for the purposes of monitoring the interface.

Deactivation conditions for cruise control

Reversible ”easy” deactivation:

• negative deviation of vehicle speed from cruise control speed for too long (speed setting exceeded by more than 16 km/h for at least 30 seconds)
  
• vehicle speed below lower deactivation limit (< 23 km/h)
  

Reversible quick deactivation:

• Clutch operated
  
• Brake operated
  
• bottom engine speed threshold undershot (n < 1000 rpm)
  
• change of ratio of vehicle road speed to engine speed outside allowable limits (change > 0.002 (km/h)/(rpm))
  
• Intervention by DSC/ASC
  
• No valid gear engaged
  
• Aquaplaning detected (difference between front and rear wheel speeds > 10 km/h for more than 0.5 s)
  
• Fault in signal from multifunction steering wheel
  

Irreversible quick deactivation:

• Fault at brake light switch detected
  
• Fault in signal from multifunction steering wheel
  
• Speed sensor defective
  
• Fault at clutch switch detected
  
• Fault in road speed signal
  
• Impact detected
  
• Heavy deceleration detected (< 8 m/s²)
  
• Heavy acceleration detected (> 8 m/s²)
  

The active switch-off conditions can be read out in the test module.

Troubleshooting

The following faults at the MFL interface can be detected:

• 4A30, Toggle bit fault
  
• 4A31, Signal has frequency error
  
• 4A32, No signal from multifunction steering wheel
  
• 4A33, Signal from multifunction steering wheel implausible
  

Consequence: Deactivation of vehicle speed control