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Rpm control, function - GF07.10-P-1008OM

ENGINE 651.9 in MODEL 204 (except 204.9) up to 5/31/12, 204.9 up to 5/31/12 

ENGINE 651.9 in MODEL 207, 212 (except 212.098/298) up to model year 2014 

ENGINE 651.9 in MODEL 218 up to model year 2014 

Function requirements for RPM control, general points 

Rpm control, general 

Rpm control stabilizes the idle speed and limits the engine speed to protect the engine and the drivetrain. Based on the signal from the crankshaft position sensor (L5) (except code (B03) ECO start/stop function) or the crankshaft Hall sensor (B70) (with code (B03) ECO start/stop function), the CDI control unit (N3/9) recognizes the engine RPM.

For RPM limitation the CDI control unit reads in the following sensors and signals:

IMPORTANT The Electronic Stability Program control unit will be used in service as of 1.3.2011 (model 204.0/2.) or as of 1.6.2011 (model 204.3) in 2 variants:

Until 28.2.2011 (model 204.0/2.) or 31.05.2011 (model 204.9) and as of 1.6.2011 (model 204.9) only the basic variant of the Electronic Stability Program control unit will be used.

The engine speed is regulated by the CDI control unit by the following measures:

The natural vibration of the engine at idle is regulated in the following manner by the CDI control unit:

Function sequence for RPM control 

Regulation of the engine speed is described in the following steps:

Function sequence for torque converter protection 

To protect the torque converter in selector lever positions "P" or "N" (no power flow) from excessive static internal pressure, the maximum engine speed is limited to approx. 4200 RPM.

The CDI control unit receives information on the current selector lever position from the electronic transmission control unit or the fully integrated transmission controller unit via the drive train CAN.

Function sequence for maximum engine speed limitation 

During travel, the maximum engine speed is limited to 4500 RPM for a speed >0 in order to protect the engine from the effects of inadmissibly high engine speeds.

The CDI control unit detects the driving mode based on the "vehicle speed" CAN signal, which is transmitted from the Electronic Stability Program control unit via the chassis CAN.

Function sequence for idle speed control 

The CDI control unit regulates and stabilizes the idle speed depending on operating conditions and engine loads if the accelerator pedal is not actuated.

For idle speed control the CDI control unit also reads in the following sensors and signals:

The CDI control unit subsequently regulates the fuel pressure in the rail via the quantity control valve and the pressure regulating valve and the injection time via actuations of the fuel injectors.

IMPORTANT The fuel pressure in the rail and the injection time of the fuel injectors determine the injection quantity.

IMPORTANT The switchable engine mounts prevent transfer of low frequency natural vibration from the engine when idling. When driving they act as hydraulic engine mounts. They are controlled by the CDI control unit. The CDI control unit regulates the idle speed in the following operating and engine load conditions:

Engagement of the gear range "D" or "R" (with an automatic transmission) 

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. For this purpose the CDI control unit evaluates the "engaged gear range" CAN signal from the electronic transmission control unit or the fully integrated transmission controller unit.

IMPORTANT For vehicle with an automatic transmission the idle speed is 750 RPM and for vehicles with a manual transmission the idle speed is 810 RPM.

Actuation of the clutch pedal (with a manual transmission) 

The CDI control unit recognizes actuation of the clutch pedal or clutch pedal switch and regulates the engine speed to obtain a stable idle speed.

Switching in the A/C compressor (A9) 

When the engine is at idle, so that engine speed will not fall when the refrigerant compressor is switched-in, the automatic air conditioning control and operating unit sends a status signal to the CDI control unit before the AAC is engaged.

The CDI control unit adapts the idle speed appropriately.

IMPORTANT If the following conditions exist, the CDI control unit interrupts switching in of the A/C compressor:

On-board electrical system battery undervoltage (G1) 

The CDI control unit recognizes an undervoltage of the on-board electrical system battery via the "circuit 30" and increases the idle speed in combination with the automatic transmission for an engaged gear range "D" or "R" up to switch off of the engine at around 100 RPM.

IMPORTANT Diagnosis

The basic setting of the idle speed can be read out and influenced using the Xentry Diagnostics.

  Electrical function schematic for RPM control MODEL 204 PE07.10-P-2708-97FAE
  Electrical function schematic for RPM control MODEL 207 PE07.10-P-2708-97EAE
  Electrical function schematic for RPM control MODEL 212 PE07.10-P-2708-97DAE
  Electrical function schematic for RPM control MODEL 218 PE07.10-P-2708-97XAD
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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