System functions

The following graphic shows the functional networking of the fully automatic trailer tow hitch in simplified terms, using the example F11.

Fig 1: Rear Lid Contact Switch Functional Networking

Courtesy of BMW OF NORTH AMERICA, INC.

The following graphic shows the functional networking of the fully automatic trailer tow hitch in simplified terms, using the example F15.

Fig 2: KOMBI Functional Networking

Courtesy of BMW OF NORTH AMERICA, INC.

The following graphic shows the functional networking of the fully automatic trailer tow hitch in simplified terms, using the example F30.

Fig 3: Rear Electronic Module Functional Networking

Courtesy of BMW OF NORTH AMERICA, INC.

• Automatic inward and outward pivoting 

  Briefly pressing the button (for less than 1 second) pivots the ball head fully automatically from one end position to the other. Fully automatic pivoting out or in cannot be halted by briefly pressing the button a further time.

  Fully automatic pivoting out or in can only then be started when the ball head is in one of the two end positions.

• Reversing the pivoting movement 

  If during fully automatic pivoting out or in the permitted DC motor power consumption is exceeded (e.g. due to an obstruction or stiff movement at low ambient temperature): The trailer module (AHM) initiates reversing for the fully automatic trailer tow hitch. The ball head's pivoting movement is halted. The ball head is pivoted back in the other direction (reverse). Reversing is suppressed close to either end position and a higher current consumption is permitted. This allows the ball head to be pivoted out of each end position with more force (e.g. to release the ball head if stuck).

• Initialization 

  When initializing, the entire swivel angle and both end positions of the ball head are recorded in the trailer module (AHM). The end stops are stored in the trailer module (AHM).

  If the initialization of the fully automatic trailer tow hitch is lost, the red LED in the button for the fully automatic trailer tow hitch will flash or light up.

  • Sequence for manual initialization: 

    Press the button and hold it until the trailer tow hitch has completely moved in the direction of the work position and back to the rest position.

    NOTE: If the trailer tow hitch stops in an end position, but the LED does not light up green, the button must be released briefly. Next, press the button again until the other end position is reached.

    The LED will continue to flash until the initialization is finished. Next, it will light up green continuously.

    If the initialization was unsuccessful, repeat the procedure or run the initialization with the diagnosis 

  If it is still not possible to carry out the initialization, another fault must be present:

  • Mechanics not running smoothly
  • Components in electric motor (e.g. direct current motor, hall effect sensor, switch) or wiring harness faulty

  During the initialization process, the maximum current of the drive motor is permitted and reversing of the ball head is suppressed.

• Signalling via the indicator light in the button for the fully automatic trailer tow hitch 

  The indicator light in the button for the fully automatic trailer hitch is a 2-colored LED (red and green). The indicator light is activated directly by the trailer module (AHM).

  The indicator light shows the system status. The following signalling is possible:

  • Indicator light off:
    • Conditions required for switch-on not met
    • System not operational, e.g. due to blown fuse or broken lead
  • Indicator light lights up green:
    • Ball head locked in one of 2 end positions (rest position or operating position) and switch-on conditions fulfilled
  • Indicator light flashes green:
    • Ball head is moving (ball head pivoting out or in)
  • Indicator light lights up red:
    • Ball head in intermediate setting (not in rest position or operating position)
    • Trailer module (AHM) not initialized
• Adjusting the trailer hitch 

  To ensure that the trailer tow hitch remains pivoted in the end position, the direct current motor is regularly briefly activated in the direction of the end stop. The trailer module (AHM) activates the readjustment under the following preconditions: Terminal 15 ON and ball head pivoted out in end position or operating position.

• Breakaway function 

  Cyclical readjustment of the pivoted-out ball head can result in the ball head becoming mechanically jammed. In this event, the ball head can be freed from the end stop by the breakaway function. A defined swivel motion must be achieved in the initial phase for pivoting the ball head out or in. This swivel motion corresponds to a defined number of hall signals from the direct current motor. The Hall pulses are picked up by the Hall effect sensor on the DC motor. If a defined number of hall signals is not  reached, the trailer module (AHM) activates the breakaway function.

  In the breakaway function, the direct current motor is periodically activated several times (example: per cycle, activated for 500 ms with subsequent pause of 500 ms). If the minimum number of hall signals are not achieved, the ball head can then only be pivoted in or out by continuous operation of the button for the electrically pivoted trailer tow hitch.

• Emergency operation 

  If the voltage supply is interrupted during operation, various signal statuses could be lost. When power is available again, the button must be pressed and held for 5 seconds. This will switch the powertrain on (emergency operation).

• Undervoltage and overvoltage 

  The trailer module (AHM) detects undervoltage and overvoltage.

  Undervoltage: Vehicle voltage less than 9 V.

  Overvoltage: Vehicle voltage greater than 16 V.

  If overvoltage or undervoltage is detected during pivoting in or out of the ball head, the ball head still pivots as far as the end position. The fault is then indicated by the LED in the button. If an overvoltage or undervoltage is detected during continuous operation of the button for the fully automatic trailer hitch, the ball head can still be pivoted into the end position. The ball head's pivoting movement stops when the button is released. The DC motor can then no longer be energized while the overvoltage or undervoltage persists.

• Trailer lighting 

  The trailer module (AHM) activates the trailer lighting circuits:

  • Brake light
  • Side lights
  • Parking light
  • Turn indicator
  • Hazard warning flashers
  • Crash-Alarm-Hazard warning flashers
  • Flash in the case of DWA alarm
  • Rear fog light
  • Reversing light.

  Depending on the series and trailer tow hitch version, the trailer module (AHM) is supplied with voltage via terminal 30F and terminal 30B. If a voltage supply fails, the lighting function is limited. In emergency operation only certain load circuits remain active.

  If undervoltage is detected, all lighting functions are retained (exception: failure of the relevant CAN signal or failure of the entire CAN bus).

  In the event of overvoltage, the effective tension is heavily reduced by means of pulse width modulation to prevent overload current. A temperature sensor is installed on the printed circuit board with the semiconductor switches. The temperature value serves as input value for configuration of the pulse-width modulated signal (PWM signal).

  The trailer module (AHM) receives the brake light activation signal via the CAN bus and via a redundant signal line. Thus the brake lights can be activated continuously as a safety function in case of failure of the microcontroller in the trailer module (AHM) or of the CAN bus. It is possible that the two turn signal bulbs light up when the brake lights are activated (due to the encodable national-market versions).

  If the rear fog light on the trailer fails, this switches over to the rear fog light of the towing vehicle.

• Trailer detection 

  The trailer module (AHM) detects a trailer as connected when at least one load is detected by hot monitoring or 2 loads by cold monitoring on the lighting system. The trailer module (AHM) then transmits the message "Trailer connected" on the K-CAN. This message is translated by several control units in the towing vehicle. This deactivates the rear ultrasonic sensors and the rear fog light on the towing vehicle, for example.