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RPM control, function - GF07.10-P-1008OGG

ENGINES 642.8 in MODEL 164.1 as of model year 2009/YoM 08 model refinement package 

ENGINES 642.8 in MODEL 164.8, 251.1 as of model year 2009/YoM 08 

ENGINES 642.8 in MODEL 251.0/1 as of model year 2011/YoM 10 model refinement package 

Function requirements for RPM control, general points 

RPM control, general points 

RPM control stabilizes the idle speed and limits the engine speed to protect the engine and the drive train. On the signal from the crankshaft Hall sensor (B70), the CDI control unit (N3/9) detects the engine speed.

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

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

Function sequence for RPM control 

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

Function sequence for torque converter protection 

In order 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 the information about the current selector lever position from the electric controller unit (VGS) over the engine compartment 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 on the "vehicle speed" CAN signal, which is sent by the ESP control unit via the engine compartment CAN.

Function sequence for maximum speed limit 

Upon reaching 250 km/h the injection times of the fuel injectors are reduced by the CDI control unit and the fuel pressure in the rails is reduced via the quantity control valve and the pressure regulating valve. These measures ensure simple maximum speed limitation the reduction of the engine torque.

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

Function sequence for idle speed control 

The idle speed control 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 idle speed can raised for a limited time to about 1600 RPM depending on the atmospheric pressure and ambient temperature. The CDI control unit regulates the idle speed in the following operating and engine load conditions:

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. To do this, the CDI control unit evaluates the "gear range engaged" CAN signal from the electric controller unit (VGS).

Switching on refrigerant compressor 

In order to ensure that the motor speed in idle does not drop upon switching on of the refrigerant compressor, the AAC [KLA] control and operating unit (except code (581) Comfort automatic air conditioning) or the comfort AAC control and operating unit (with code (581) Comfort automatic air conditioning) sends a status signal to the CDI control unit before switching on.

The CDI control unit adapts the idle speed appropriately.

IMPORTANT For the following conditions the CDI control unit interrupts switching on of the refrigerant compressor:

Battery (G1) undervoltage 

The CDI control unit recognizes an undervoltage of the battery over "circuit 30" and increases the idle speed for an engaged gear range "D" or "R" up to switch off of the engine at about 100 RPM.

IMPORTANT Diagnosis

The basic setting of the idle speed can be read out and adjusted with the Diagnosis Assistance System (DAS.

REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for RPM control Model 164   PE07.10-P-2708-97MAA
Model 251   PE07.10-P-2708-97RAA
  Component description for CDI control unit N3/9   GF07.16-P-6000OGU 
  Component description for automatic air conditioning control and operating unit N22 Except code (581) Comfort automatic air conditioning GF83.40-P-3000GM
  Component description for comfort automatic air conditioning control and operating unit N22/7 with code (581) Comfort automatic air conditioning GF83.40-P-3010GM
  Component description for ESP control unit N47-5   GF42.45-P-5118GM
  Component description for central gateway control unit N93   GF54.21-P-4170GM
  Component description for fully integrated transmission control unit Y3/8n4   GF27.60-P-5165AHZ
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