RPM Control, Function - GF07.10-P-1008MRT

Engine 256.9 in model 213, 238, 257, 290 

up to model year 2021 

Engine 256.9 in model 222 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects the engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

RPM control, general 

The RPM control stabilizes the engine speed in neutral and limits the engine speed to protect the engine, the drivetrain and the vehicle.

For RPM control, the ME-SFI [ME] control unit reads in the signals of the following components:

• Crankshaft Hall sensor
• Throttle valve actuator (M16/6)
  • Actual value potentiometer 1 (M16/6r1)
  • Actual value potentiometer 2 (M16/6r2),

The ME-SFI [ME] control unit also evaluates the following signals:

• Wheel speeds

  The Electronic Stability Program control unit (N30/4) transmits the wheel speeds via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit.

• Drive position

  The control unit of the fully integrated transmission control electric controller unit (Y3/8n4) transmits information about the engaged drive range via the drive CAN to the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit regulates the engine speed via the following measures:

• Adjusting the opening angle of the throttle valve
• Adjusting the injection duration of the fuel injection system
• Advanced or retarding the ignition angle

The engine responds more quickly to the ignition angle setting than to the throttle valve setting.

The ME-SFI [ME] control unit actuates the following components for this purpose:

• Throttle valve actuator
  • Throttle valve actuator motor (M16/6m1)
• Fuel injection system
  • Cylinder 1 fuel injector (Y76/1)
  • Cylinder 2 fuel injector (Y76/2)
  • Cylinder 3 fuel injector (Y76/3)
  • Cylinder 4 fuel injector (Y76/4)
  • Cylinder 5 fuel injector (Y76/5)
  • Cylinder 6 fuel injector (Y76/6)
• Ignition system
  • Cylinder 1 ignition coil (T1/1)
  • Cylinder 2 ignition coil (T1/2)
  • Cylinder 3 ignition coil (T1/3)
  • Cylinder 4 ignition coil (T1/4)
  • Cylinder 5 ignition coil (T1/5)
  • Cylinder 6 ignition coil (T1/6)

  RPM limitation 

  In selector lever position "N" or "P" (no power transmission), the maximum engine speed is limited to approx 4200 RPM to protect the torque converter against excessively high static internal pressure.

  In order to protect the engine from inadmissible engine speeds during driving mode, the maximum engine speed is limited to about 6000 RPM.

  Driving operation is defined via the wheel speeds.

  I n the case of a defective throttle valve actuator motor of the throttle valve actuator, the maximum engine speed in idle is limited to approx. 1400 RPM and during vehicle operation to approx. 1800 RPM.

  Maximum vehicle speed limit 

  On reaching the maximum speed, the opening angle of the throttle valve and the injection duration are reduced by the ME-SFI [ME] control unit. The engine torque is thus reduced and the speed is limited.

  Idle speed control 

  The idle speed is regulated depending on the operating conditions and engine load.

  For idle speed control, the ME-SFI [ME] control unit reads in the signals of the following sensors:

  • Coolant temperature sensor (B11/4)
  • Pressure and temperature sensor downstream of turbocharger (B28/17)

  The ME-SFI [ME] control unit regulates the idle speed under the following operating conditions and engine loads:

  • Warm-up 
  • Engaging drive range "D" or "R" (transmission 725) 
  • Undervoltage in the on-board electrical system 
  • Purging Warm-up 

  The ME-SFI [ME] control unit also evaluates the on-board electrical system utilization and the air conditioning system requests.

  12 V on-board electrical system operating rate 

  The front SAM control unit (N10/6) transmits the idle speed increase request and the specified alternator voltage via the interior CAN (CAN B), the electronic ignition lock control unit (N73), the suspension FlexRay, the powertrain control unit, and the engine CAN (CAN C) to the ME-SFI [ME] control unit.

  48 V on-board electrical system operating rate 

  On the basis of current consumers, the charge level of the 48 V on-board electrical system battery (G1/3), and further criteria, the powertrain control unit calculates the value to which the idle speed is to be increased. The DC/DC converter control unit (N83/1) transmits the status of the 48 V on-board electrical system battery and information on the on-board electrical system operating rate via the interior CAN, the electronic ignition lock control unit, and the suspension FlexRay to the powertrain control unit. The powertrain control unit transmits the idle speed increase request via the engine CAN to the ME-SFI [ME] control unit.

  Air conditioning 

  The climate control control unit (N22/1) transmits idle speed increase requests via the interior CAN, the electronic ignition lock control unit, the suspension FlexRay, the powertrain control unit, and the drive CAN to the ME-SFI [ME] control unit.

  In the warm-up phase, the idle speed is regulated depending on the coolant temperature in order to bring the catalytic converter more quickly to operating temperature after engine start.

  Additional function requirements for starting the warm-up phase:

  • Coolant temperature below 40°C.
  • Gear range "N" or "P" engaged

  The ME-SFI [ME] control unit increases the idle speed for approx. 20 s to between 1100 and 1300 RPM. The idle speed is subsequently increased for a coolant temperature below 70°C for approx. 50 s by 50 to 100 RPM.

  Engagement of gear range "D" or "R" 

  When gear range "D" or "R" is selected, the idle speed is set to a lower value to reduce the tendency of the vehicle to creep forward.

  Undervoltage in the on-board electrical system 

  An undervoltage is detected by the ME-SFI [ME] control unit via circuit 30. The idle speed is then, with engaged drive range "D" or "R", increased by approx. 100 RPM until the ignition is switched off.

  Purging 

  The idle speed control prevents any change in the engine speed due to purging.

  The basic setting of the idle speed can be read out and modified via the diagnostic tester.

  	Electrical function schematic for RPM control	Engine 256.9 in model 213, 238 up to model year 2021	PE07.10-P-2708-97DBA
  		Engine 256.9 in model 222	PE07.10-P-2708-97SEM
  		Engine 256.9 in model 257 up to model year 2021	PE07.10-P-2708-97XBB
  	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRT