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Parking system, function - GF54.65-P-0006CAM

MODEL 207.3/4 as of model year 2014 with CODE 235 (Active Park Assist) 

Fig 1: Parking System Block Diagram
G10081843Courtesy of MERCEDES-BENZ USA

Function requirements, general 

IMPORTANT The status of circuit 15 is sent by the electronic ignition lock control unit via the interior CAN, front SAM control unit and chassis CAN 2 to the parking system control unit.

Parking system, general 

The parking system uses the ultrasonic measuring procedure to register the distance between the vehicle and an obstacle. While driving at speeds of v < 36 km/h, parallel or perpendicular parking spaces on both sides of the vehicle in the direction of travel are measured, stored and the vehicle is moved in and out of a parking space semi-automatically upon the request of the driver.

IMPORTANT Semi-automatic exiting of perpendicular parking spaces is not available.

The parking system warning indicators visually inform the driver of the respective distance between the vehicle and the obstacle. An acoustic warning can also be issued via the warning buzzer in the instrument cluster.

IMPORTANT In certain situations, warnings from the parking system are suppressed, e.g. when reversing through narrow passages (driveway).

There is an obstacle within the detection range but, based on the current steering wheel position, a collision will not take place.

Parking system operation is dependent on speed and direction of travel, and therefore the following input factors have to be determined:

Vehicle speed and direction of travel:

The direction of travel is defined using the wheel rotation direction. The vehicle speed is calculated from the wheel speed.

The Electronic Stability Program control unit sends the relevant information via chassis CAN 1, front SAM control unit and chassis CAN 2 to the parking system control unit and to the instrument cluster. The parking system control unit calculates the vehicle speed and defines the direction of travel. At the same time the instrument cluster also calculates the speed to be displayed and sends it over the chassis CAN 2 to the parking system control unit.

Reverse gear or gear range "R" engaged:

Vehicles with transmission 722.9, 725:

The fully integrated transmission control unit sends information on the engaged gear range via the drive train CAN, the CDI control unit or ME-SFI control unit, chassis CAN 1, front SAM control unit and chassis CAN 2 to the parking system control unit.

Vehicles with transmission 711 or 716:

Engaging of the reverse gear is defined by the status of the backup lamp switch. The front SAM control unit reads in the status of the backup lamp switch directly and sends it via chassis CAN 2 to the parking system control unit. If the reverse gear is not engaged, it is assumed that one of the forward gears is engaged.

The parking system includes the following subfunctions:

Illustration of the principle for measuring procedure 

Fig 2: Principle For Parking System Measuring Procedure
G10081844Courtesy of MERCEDES-BENZ USA

Measuring procedure function sequence 

The parking system is based on the ultrasonic measuring procedure. In the process, the parking system distance sensors are actuated by the parking system control unit. As a result of this these emit an ultrasonic signal. The ultrasonic waves reflected by an obstacle are received again by the distance sensors. The parking system control unit directly reads in the signals of the distance sensors and evaluates them. In principle a distinction is made between two measurements. On the one hand the direct measurement, resulting from a direct echo and on the other hand the indirect distance measurement which is achieved via a cross echo. Echoes can usually also be received from adjacent distance sensors due to the large distance sensor detection angles; these are known as cross echoes. These occur at the obstacle due to scattered reflection. The distance between the vehicle and obstacle can be calculated from two echo signals using the triangulation method. The propagation times of the signals from the direct measurement and from the cross measurement are required for this method. A long signal runtime thus equals a long distance between the vehicle and the obstacle, a short signal runtime equals a short distance between the vehicle and the obstacle.

IMPORTANT The parking system may not work correctly in some cases because of the functional principal (sending and receiving of ultrasound waves).

So for example, when approaching a strong sound absorbent obstacle (e.g. a vehicle covered in snow) it is possible that false data may be displayed.

Fig 3: Measuring Parking Distance Procedure - Illustration Shows Model 207.3
G10081845Courtesy of MERCEDES-BENZ USA

Illustration shows model 207.3 

The distance sensors are activated according to the direction of travel.

The distance sensors responsible for monitoring the front area (A) and the front corner protection area (B) are activated when the vehicle is moving forward.

The distance sensors responsible for monitoring the rear corner protection area (C) and the rear area (D) are also activated when the vehicle is moving backward.

The monitored front area is max. s = 100 cm.

The monitored rear area is max. s = 120 cm.

If the distance between the vehicle and an obstacle is less than s = 20 cm (c, e), the parking system will for technical reasons no longer receive any defined data.

Below a speed of v = 36 km/h, the parking space detection range at the right and left of the vehicle is measured in the horizontal depth up to a distance of s = 400 to 450 cm, and stored for s = 15 m in the parking system control unit.

Self-test function sequence 

During the self-test the following components are checked for proper operation:

Parking system control unit self-test:

The parking system control unit performs a self test after the ignition is switched on (circuit 15 ON). In the process, the hardware of the parking system control unit is tested.

IMPORTANT The engaged gear range (with transmission 722.9, 725) or the status of the backup lamp switch (with transmission 711, 716) does not influence the self-test of the parking system control unit.

Distance sensor self-test:

A self-test of the distance sensors (e.g. for connection) is only performed when a distance sensor is "pulsed" (activated) (ultrasonic waves are transmitted).

IMPORTANT Engaging reverse gear (with transmission 711, 716) or gear range "R" (with transmission 722.9, 725) influences the self-test of the distance sensors. If reverse gear or gear range "R" has been engaged, all distance sensors are tested. If reverse gear or gear range "R" has not been engaged, only the front distance sensors are tested.

Distance sensor test for subsequent vibrations:

A distance sensor test for subsequent vibrations (acoustic/physical function of the distance sensor) is performed cyclically.

Function test on parking system warning indicators:

When the ignition is switched on (circuit 15 ON), the parking system control unit fully actuates all display elements in the rear parking system warning indicators and in the instrument panel parking system warning display for approx. t = 1 s.

If there are no malfunctions or faults, the two yellow horizontal "standby" bars light up in the parking system warning indicator. The parking system control unit carries out further self-tests at regular intervals.

The following states can be recorded here:

If there is a malfunction or system error, the parking system is deactivated and the LED in the parking system button lights up.

For this purpose, the parking system control unit sends the corresponding request via chassis CAN 2 to the front SAM control unit, which actuates the LED in the parking system button via the instrument panel LIN.

Malfunction:

A malfunction can be caused by a temporary external disturbance (e.g. a jackhammer on a construction site, a steam jet or by driving through an automatic car wash). If a malfunction occurs during operation, this is indicated by illumination of the red display elements in the currently actuated parking system warning indicator.

To do this, the parking system control unit actuates the parking system warning indicators directly.

If a malfunction persists, the cause thereof is identified while driving by means of a self-test. If the malfunction is still present, this is interpreted as a system error.

IMPORTANT A warning sound is not emitted.

System fault(s)

A system fault can have the following causes:

If a system error is detected, the red display elements of the rear parking system warning indicator or those of the instrument panel parking system warning indicator light up depending on whether reverse gear (with transmission 711, 716) or gear range "R" (with transmission 722.9, 725) is engaged or not. An acoustic warning is also emitted for t = 2 s.

For this purpose, the parking system control unit actuates the respective parking system warning indicator directly. In addition, the parking system control unit transmits the request to output a warning to the instrument cluster via chassis CAN 2. The instrument cluster then directly actuates the warning buzzer. After t = 3 s, the parking system switches off. A fault is entered in the fault memory of the parking system control unit, and the LED in the parking system button lights up.

If the system error occurs again after an ignition cycle, the described scenario is repeated.

IMPORTANT The size of the license plate bracket attached to the bumper varies depending on the national version. Due to the different dimensions and shapes the parking system must be adapted to the particular circumstances. The national version can be coded via the diagnosis tester in order to avoid malfunctions.

Behavior in the event of overvoltage and undervoltage function sequence 

The parking system behavior in the event of overvoltage or undervoltage is described in the following table.

On-board electrical system voltage U < 9.0 V On-board electrical system voltage U > 16.0 V Undervoltage with reset Undervoltage without reset (start pulse)
Parking system nonfunctional Parking system nonfunctional The function is activated again after a reset Display of distance
Parking system warning indicators, dark Parking system warning indicators, dark No function test of parking system warning indicator Start pulse has no influence on parking system
No function test, if voltage returns to normal No function test, if voltage returns to normal - No function test of parking system warning indicator
LED in parking system ON button LED in parking system ON button - -

Additional function requirements for activation and deactivation 

Deactivate and activate function sequence 

The parking system can be manually deactivated or activated by pressing the parking system button in the upper control panel. The front SAM control unit reads in the status of parking system button via the instrument panel LIN and sends it via chassis CAN 2 to the parking system control unit.

IMPORTANT If the parking system has been switched off manually using the parking system button, the function is switched on again automatically when circuit 15 is activated again.

The intensity of the parking system warning indicator illumination for an activated parking system changes depending on the ambient brightness.

The ambient brightness is sensed by the rain/light sensor. The rain/light sensor sends information on the ambient brightness (dusk/dawn level) via the wiper/inside rearview mirror LIN, front SAM control unit and chassis CAN 2 to the parking system control unit. If the rain/light sensor detects "Night", the parking system warning indicator is actuated at 60 % brightness. If the rain/light sensor detects "Day", the parking system warning indicator is actuated at 100 % brightness.

When the parking system is deactivated, only the light-emitting diode in the parking system button lights up. The parking system control unit sends a corresponding request via chassis CAN 2 to the front SAM control unit, which actuates the LED in the parking system button via the instrument panel LIN. When driving the parking system switches to standby mode between v = 60 and 16 km/h. In other words, the parking system control unit, the parking system warning indicators and the distance sensors are still supplied with power but the parking system warning indicators are switched to "dark".

Additional function requirements for monitoring reverse travel 

IMPORTANT The trailer recognition control unit (with CODE 550 (Trailer hitch)) sends the "trailer detected" status via the interior CAN, front SAM control unit and chassis CAN 2 to the parking system control unit.

Function sequence for monitoring reverse travel 

During reverse travel the areas in front of and behind the vehicle are monitored. When the lower limit speed of v = 16 km/h is dropped below, the parking system changes to measuring mode. When obstacles are detected in front of or behind the vehicle, the driver is initially visually warned by illumination of the appropriate warning segments of the parking system warning indicators. The parking system control unit actuates the parking system warning indicators directly. When dropping below a distance of s = 30 cm, the warning is then intensified by an intermittent tone and subsequently by a continuous signal. The parking system control unit sends the request to output a warning to the instrument cluster via chassis CAN 2. The instrument cluster then directly actuates the warning buzzer. When the upper speed limit of v = 18 km/h is exceeded, the parking system goes over into stand by mode again.

IMPORTANT If gear range "R" (transmission 722.9) or reverse gear (transmission 711, 716) is engaged immediately after the engine is started, no acoustic warning is issued, even if an obstacle is located immediately in front of the vehicle (only a visual warning is given).

Additional function requirements for monitoring during forward travel 

Function sequence for monitoring forward travel 

When driving forwards the area in front of the vehicle is monitored. When the lower limit speed of v = 16 km/h is dropped below, the parking system changes to measuring mode. When obstacles are detected in front of the vehicle, the driver is first warned visually by illumination of the appropriate LED in the instrument cluster parking system warning indicator. The parking system control unit actuates the instrument cluster parking system warning indicator directly. When dropping below a distance of s = 30 cm, the warning is then intensified by an intermittent tone and subsequently by a continuous signal. The parking system control unit sends the request to output a warning to the instrument cluster via chassis CAN 2. The instrument cluster then directly actuates the warning buzzer. When the upper speed limit of v = 18 km/h is exceeded, the parking system goes over into stand by mode again.

Additional function requirements, parking space recognition 

IMPORTANT The Electronic Stability Program control unit sends the status of the ESP® chassis CAN 1, front SAM control unit and chassis CAN 2 to the parking system control unit.

Parking space recognition function sequence 

The parking space detection function is used for simple locating of suitable parallel or perpendicular parking spaces. The parking space detection function is implemented via the outer front distance sensors. These monitor the area left and right of the vehicle and therefore have a larger range than the rest of the distance sensors.

IMPORTANT At a speed of v = 0 to 18 km/h the parking system operates in mixed mode between obstacle and parking space detection. As of v > 18 km/h, the parking system changes to parking space detection mode and remains active up to v = 36 km/h.

Illustration shows model 207.3 

Fig 4: Measuring Maximum Range Of Outer Front Distance Sensors For Parking Space Detection - Illustration Shows Model 207.3
G10081846Courtesy of MERCEDES-BENZ USA

The range of the outer front distance sensors is max. s = 400 to 450 cm, depending on environmental influences (e.g. rain, snowfall, air humidity, extreme temperatures of e.g. T = -40 or +85 °C, air pressure, hot engine air). Data from the outer front distance sensors are read in and evaluated by the parking system control unit directly. It is calculated whether the parking space is suitable for the vehicle from the stored vehicle dimensions and deviations of the recorded parking space.

Minimum size of a parallel parking space (parallel to the direction of travel):

Minimum size of a perpendicular parking space:

IMPORTANT For parallel and perpendicular parking, two boundary points are always required.

After the driver has engaged gear range "R" (with transmission 722.9, 725) or reverse gear (with transmission 711, 716), the query "Activate Park Assist?" and the warning notice "Pay attention to surroundings" appear in the multifunction display of the instrument cluster. In addition, the possibility of activating the Active Park Assist is also provided in the multifunction display of the instrument cluster. For this purpose, the parking system control unit sends the requests to output the appropriate symbols in the multifunction display to the instrument cluster via chassis CAN 2. The symbols shown in the multifunction display correspond to the OK button in the left multifunction steering wheel button group for "Yes" (activate) or the "Back" and voice control system OFF button for "No" (do not activate).

The steering column tube module control unit reads in the control signals from the left multifunction steering wheel button group via the steering LIN and steering wheel electronics and sends these signals via chassis CAN 1, the front SAM control unit and chassis CAN 2 to the instrument cluster. Depending on the response to the message, the instrument cluster sends the appropriate status of the Active Parking Assist to the parking system control unit via chassis CAN 2.

IMPORTANT The parking system detects an empty space which is geometrically suitable for parking. The parking system does not recognize whether the empty space is actually suitable as a parking space.

Parking space detection, illustration of the principle 

Fig 5: Principle For Parking Space Measuring Procedure
G10081847Courtesy of MERCEDES-BENZ USA

IMPORTANT The trajectory, which consists of two arcs, forms the path to be taken into the parking space.

Additional function requirements for display of possible parking spaces on instrument cluster 

Function sequence for display of possible parking spaces on instrument cluster 

When the parking system is searching for a parking space, a P symbol (6) appears in the multifunction display of the instrument cluster. As soon as an appropriate parking space is detected by the parking system, a left directional arrow (7) or a right directional arrow (8) also appears in addition to this symbol that indicates the side of the vehicle on which the parking space is located.

Parking spaces are always looked for on both sides of the vehicle. However, only parking spaces on the passenger side are pointed out by default. To also allow parking spaces on the driver side to be displayed, the driver must actuate the turn signal in the appropriate direction. The parking system control unit sends the request to activate the display in the instrument cluster via chassis CAN 2 to the instrument cluster.

The steering column tube module control unit reads in the switch position of the combination switch directly and sends the position information via chassis CAN 1, the front SAM control unit and chassis CAN 2 to the parking system control unit.

IMPORTANT Changes to the parking situation after parking space detection are not considered by the parking system.

Additional function requirements for semi-automatic parking 

Function sequence for semi-automatic parking 

If the Park Assist has detected a suitable parallel or perpendicular parking space and the parking procedure has started, various driving instructions and messages are shown to the driver in the multifunction display of the instrument cluster. The driver can now take the hands off the steering wheel. The Park Assist steers the vehicle into the parking space by means of targeted steering movements. All the driver has to do is accelerate.

The parking system control unit calculates the required steering angle from the size of the parking space and the position of the vehicle relative to the space. The actual steering angle is recorded by the steering angle sensor. The steering column tube module control unit reads in the data from the steering angle sensor directly and sends information on the steering angle via chassis CAN 1, the front SAM control unit and chassis CAN 2 to the parking system control unit. The parking system control unit sends corresponding steering commands to the electrical power steering control unit via chassis CAN 2. The electrical power steering control unit actuates the requests to match the electric power steering actuator motor. The steering gear converts the rotation movement of the electric power steering actuator motor into a parallel movement. The parking system control unit monitors the gear rack travel of the steering gear when this takes place. This is recorded by the electric power steering torque sensor. The electrical power steering control unit reads in the signals from the electric power steering torque sensor directly and sends corresponding information via chassis CAN 2 to the parking system control unit.

The parking system control unit transmits the appropriate requests to issue driving instructions and messages to the instrument cluster via chassis CAN 2.

The following driving instructions or messages can be displayed:

After each gear range change, the driver is required to continue controlling vehicle movement until the end position has been reached. At a speed of v = 7 km/h, the multifunction display shows the "Park Assist only up to 10 km/h" note. If the vehicle (front or back) reaches a distance of s < 30 cm to the parking space boundary, the driver is notified by illumination of the first red LED in the parking system warning indicators. The warning buzzer additionally issues a warning tone. Delimitation at the side of the parking space is defined by a recognized obstacle (e.g. a curb or pole). If an obstacle is not detected at the side, the vehicle is aligned flush to the front or rear obstacle. If the vehicle is not positioned straight in the parking space, this is corrected by the Active Parking Assist in a maximum of seven maneuvers. The wheels are straightened once the parking procedure has been completed. As soon as this end position is reached, the "Parking assistance completed - Please take over" message is shown for a period of t = 5 s on the multifunction display. In addition, a warning tone is sounded. The target parking position of the vehicle is generally as far back and deep into the parking space as possible.

On vehicles with transmission 722.9, the vehicle brakes automatically without driver intervention as it approaches the target parking position, a maneuvering point or an obstacle. In principle a distinction is made between two types of deceleration:

A comfort stop is made at the end of a regular parking maneuver as soon as the vehicle approaches the target parking position or maneuvering points. Deceleration is performed proportionally. If an unforeseeable situation arises which requires immediate braking of the vehicle (e.g. a person enters the sensing range, the door of an adjacent vehicle is opened), an emergency stop is made. The level of deceleration is as strong as possible to avoid any collision. The Electronic Stability Program control unit calculates the required braking torque and actuates the traction system hydraulic unit accordingly when the maneuvering points are reached. The parking system control unit sends information about the remaining distance to the specified obstacle to the Electronic Stability Program control unit via chassis CAN 2, the front SAM control unit and chassis CAN 1.

IMPORTANT Changes to the remaining distance to the obstacle (e.g. a person walking into the path of the vehicle) are also taken into consideration. Depending on the current driving situation, however, it is not always possible to prevent a collision in such cases.

IMPORTANT The vehicle is secured by engaging of gear range "P" (with transmission 722.9, 725) by the driver or by the standstill control in the Electronic Stability Program control unit.

Additionally, the warning buzzer issues a warning tone.

The target position of the vehicle it generally as far back and deeply into the parking space as possible.

The following situations lead to deactivation of the Park Assist:

IMPORTANT If the parking system is deactivated as a result of the situations listed above, reactivation is only possible after the gear range (with transmission 722.9, 725) or the gear (with transmission 711, 716) has been changed. If the vehicle is out of the previously calculated trajectory, then the vehicle must be manually returned to the starting position, from which a new trajectory can then be calculated.

Additional function requirements for semi-automatic exit of parking space 

IMPORTANT The instrument cluster sends the status of the Active Parking Assist to the parking system control unit via chassis CAN 2.

Function sequence for semi-automatic parking space exit 

The semi-automatic parking space exit function must be preceded by semi-automatic parking of the vehicle in a parallel parking space. This ensures that the vehicle is positioned parallel to the curb, if applicable. This information is required as the Park Assist first requests "straight to the rear" vehicle movement to exit the parking space. If the vehicle was positioned in the parking space at an angle, the rims could be damaged by the curb. The semi-automatic parking space exit function is activated by actuating the turn signal indicator in the direction (left or right) in which the parking space is to be exited. The steering column tube module control unit reads in the switch position of the combination switch directly and sends the position information via chassis CAN 1, the front SAM control unit and chassis CAN 2 to the parking system control unit. On vehicles with transmission 722.9, 725, the parking system control unit evaluates the gear range status. If the gear range is not "P", the parking system control unit transmits the request "Start Parking Assist?" over chassis CAN 2 to the instrument cluster.

IMPORTANT On vehicles with manual transmission, the "Start Park Assist?" query is issued irrespective of the engaged gear.

IMPORTANT Semi-automatic parking is only possible in the direction in which the vehicle was originally parked.

The driver can then activate the semiautomatic parking space exit function using the left multifunction steering wheel button group corresponding to the driver request (exit parking space at left or right). The semiautomatic parking space exit function is activated via the OK button. Pressing the "back" and "Voice control system OFF" button cancels the procedure. The steering wheel electronics reads in the signals from the left multifunction steering wheel button group directly and sends them via the steering LIN, steering column tube module control unit, chassis CAN 1, the front SAM control unit and chassis CAN 2 to the parking system control unit. The parking system control unit then initiates the parking space exit process. The parking system control unit sends corresponding steering commands to the electrical power steering control unit via chassis CAN 2. The electrical power steering control unit actuates the electric power steering actuator motor accordingly (full steering angle). The steering gear is used to mechanically convert the electric power steering actuator motor actuation into corresponding steering movements. The parking system control unit monitors the gear rack travel on the steering gear. The electrical power steering control unit then sends the corresponding information over chassis CAN 2 to the parking system control unit.

According to the necessary maneuvering movements, the parking system control unit sends the request for visual output of the corresponding driving instructions via chassis CAN 2 to the instrument cluster.

If the vehicle reaches (forward or backward) a distance of s < 30 cm to the parking space boundary (maneuvering point), this is signaled to the driver by illumination of the first red display element in the corresponding parking system warning indicator. The vehicle is braked automatically at the corresponding maneuvering points (with transmission 722.9, 725). The Electronic Stability Program control unit receives the brake requests from the parking system control unit, and actuates the traction system hydraulic unit accordingly. Once the Park Assist has positioned the vehicle such that the driver is able to drive straight out of the parking space, the parking system control unit sends the request to display the message "Parking assistance completed - Please take over" to the instrument cluster via chassis CAN 2.

The procedure for exiting the parking space and the Active Parking Assist are aborted in the following situations:

IMPORTANT In the event of deactivation of the parking system due to the circumstances listed, reactivation requires a change of gear or gear range. If the vehicle is out of the previously calculated trajectory, then the vehicle must be manually returned to the starting position, from which a new trajectory can then be calculated.

The following messages are shown on the multifunction display in the instrument cluster:

  Electrical function schematic of parking system   PE54.65-P-2054-97EAB
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