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Cruise Control (CC), Function - GF30.30-P-0001RDM

WARNING: This page is about a different car, the 2020 Mercedes-Benz SLC43 AMG, 2019 Mercedes-Benz SLC43 AMG, 2018 Mercedes-Benz SLC43 AMG, and 2017 Mercedes-Benz SLC43 AMG. However, it is still accessible from the selected car via links, so may be relevant.

Model 172.4 

as of model year 2017 

Shown on model 172.4 

G13845632Courtesy of MERCEDES-BENZ USA

Cruise control function requirements 

Cruise control - general 

The CC function automatically regulates the vehicle speed as constant at the speed specified by the driver.

To do this the CC function evaluates the operator requests of the driver and the current driving condition.

The CC function is implemented by the Electronic Stability Program control unit.

Operation of the CC function 

G13845633Courtesy of MERCEDES-BENZ USA

The CC function can be activated over the following controls:

This sets the current vehicle speed as the target speed.

IMPORTANT If a target speed was already set since the last engine start this can be called up by actuating the switch Resume from memory. The vehicle accelerates or decelerates to the last selected target speed.

Using the switches "decelerate" and "set" and the switches "accelerate" and "set", the target speed can be altered in steps of v = 1 km/h or v = 10 km/h.

Actuation up to the actuation point increases the set speed by v = 1 km/h.

If the switch is pressed beyond the actuation point then the set speed increases each time by v = 10 km/h.

If the switch is held at or beyond the over-center preload the set speed is altered every t = 0.6 s.

The following input factors are evaluated to implement the CC function: 

Operating condition for engine/drivetrain:

The CDI control unit or the ME-SFI [ME] control unit transmits the signal "electric motor runs" or "drivetrain operational" via the chassis CAN 1 to the Electronic Stability Program control unit. Vehicle speed:

The vehicle speed is calculated on the basis of the wheel speeds. The RPM sensors detect the wheel speeds. The Electronic Stability Program control unit directly reads in the signals from the RPM sensors.

Engaged gear range (transmission 725.0):

The fully integrated transmission control unit sends the information about the gear range via drive train CAN, CDI control unit or ME-SFI [ME] control unit and chassis CAN 1 to the Electronic Stability Program control unit.

Driver request via the cruise control lever:

The driver request over the CC lever are directly read in by the steering column tube module control unit. The steering column tube module control unit transmits the control signals from the CC lever via chassis CAN 1 to the Electronic Stability Program control unit.

Accelerator pedal position:

Operation of the accelerator pedal is registered by the accelerator pedal sensor.

The CDI control unit or the ME-SFI [ME] control unit directly reads in the signals from the accelerator pedal sensor and transmits these via chassis CAN 1 to the Electronic Stability Program control unit.

The following initial parameters (request) are issued to implement the CC function: 

Raise/reduce engine torque:

The Electronic Stability Program control unit evaluates the input factors as well as further driving dynamics requests and transmits the request "increase/reduce engine torque" via the chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit implements this request.

Engage targeted gear (transmission 725.0):

The Electronic Stability Program control unit internally evaluates the input factors as well as further driving dynamics requests and transmits the request "Engage targeted gear" via chassis CAN 1, the CDI control unit or the ME-SFI [ME] control unit and drive train CAN to the fully integrated transmission control unit.

This request is however to be understood as a switching recommendation. Downshifting or upshifting of the A/T takes place autonomously itself by the fully integrated transmission control unit, dependent on the current operating condition.

Raise/reduce braking torque:

The Electronic Stability Program control unit evaluates the input factors and actuates the traction system hydraulic unit appropriately. The traction system hydraulic unit reacts by increasing or reducing the braking torque.

The cruise control function includes the following subfunctions:

Additional automatic speed control function requirements 

Function sequence for automatic speed control 

Through actuation of the "Resume from memory" switch the last set speed stored is applied, provided a set speed was stored since the last engine start. If no set speed was stored, the current vehicle speed is set as the set speed. The set speed is displayed in the speedometer.

To do this, the Electronic Stability Program control unit sends corresponding information via chassis CAN 1, front SAM control unit with fuse and relay module and chassis CAN 2 to the instrument cluster.

The following events deactivate the automatic speed control:

The following activities are started in order to reach or maintain the set speed:

The driver also has the option to accelerate beyond the set target speed through actuation of the accelerator pedal (for example when overtaking).

The set target speed is regulated again after removal of the acceleration request (releasing the accelerator pedal).

Function sequence for SPEEDTRONIC 

The SPEEDTRONIC encompasses the following subfunctions:

Additional function requirements for variable SPEEDTRONIC (without code 494 (USA version)) 

IMPORTANT Kickdown: accelerator pedal pressed by > 90% and vehicle speed v < 20 km/h less than the selected maximum permissible speed).

Function sequence for variable SPEEDTRONIC (except code 494 (USA version)) 

The maximum permissible speed of the vehicle can be limited at any time to a freely selectable value (e.g. 50 km/h in urban traffic) over the variable SPEEDTRONIC.

The driver can accelerate the vehicle up to the set limit.

If the set limit was reached, the following activities are started:

IMPORTANT If switching takes place on the variable SPEEDTRONIC on the CC lever, the automatic speed control is deactivated. The following events deactivate the variable SPEEDTRONIC:

Function sequence for permanent limiter 

The maximum permission speed of the vehicle can be limited in steps of v = 10 km/h from v = 160 km/h to 240 km/h.

Adjustment of the permissible maximum speed takes place in the menu "Settings", "Vehicle" and "Limitation (winter tires)" in the instrument cluster.

The instrument cluster sends the set maximum permissible speed via chassis CAN 2, front SAM control unit and chassis CAN 1 to the Electronic Stability Program control unit.

Approximately v = 10 km/h before reaching the set maximum permissible speed, a message appears in the multifunction display that indicates a maximum permissible speed limitation. To do this, the Electronic Stability Program control unit sends corresponding information via chassis CAN 1, front SAM control unit and chassis CAN 2 to the instrument cluster.

The driver can accelerate the vehicle up to the set permissible maximum speed.

If the maximum permissible speed was reached the following activities are started:

  Electrical function schematic for cruise control (CC)   PE30.30-P-2051-97TAD 
  Overview of system components for driver assistance systems   GF54.00-P-9998RDM
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