Trailer Lighting Module: Description and Operation

Trailer Module And Trailer Tow Hitch Release, Functional Description

Trailer module and trailer tow hitch release, functional description

This functional description describes the trailer module for the following vehicles:
- E81, E87, E90, E91, E92, E93 (BMW 1-Series, 3-Series)
- E60, E61, E63, E64 (BMW 5 Series, 6 Series)
- E65, E66, E67, E68 (BMW 7 Series)
- E70 (BMW X5)
- R55 R56 (MINI)

The following are also described:
- The control unit for the trailer tow hitch release in the E9x with the associated electrical folding trailer tow hitch and
- The control unit for the trailer tow hitch release in the E6x with the associated fully automatic trailer tow hitch

This equipment range is fitted with the optional extra 3AC "trailer coupling with electrical articulated ball end" in these vehicles. For a more detailed description of the trailer coupling releases, see: SBT 610804120.

The trailer module is an auxiliary control unit for the footwell module (E8x, E9x, E7x, R5x) or light module (E6x). At the moment, two different trailer modules are installed. The AHM3 is the version that was deployed up to 09/2006. The AHM3+ is the revised version. Essentially, it differs from the AHM3 with regard to the following characteristics:
- 2 lines and fuses for the power supply, enabling more electrical power output to be provided for the trailer lighting.

The trailer module separates the load circuits of the trailer from the circuits of the towing vehicle. The control unit also reports the status of the articulated ball head to the trailer module for the trailer tow hitch release. These states are: Trailer tow hitch locked or not locked.
The AHM3+ will be fitted as volume production launch on the E70 and R55. In all the other model series mentioned above, the AHM3+ will be fitted as of 09/ 06. Please note the following differences in the installation and function of the trailer module and of the trailer tow hitch:
- MINI The trailer module will be fitted in the R56 as a special accessory. The trailer module delivers the electrical energy for the rear bicycle rack offered as a special accessory. No trailer tow hitch is offered for the R56. A detachable trailer tow hitch is fitted in the R55.
- BMW The trailer module is fitted if the vehicle is equipped with a trailer coupling. The trailer tow hitch can be firmly installed or removable. Moreover, it is also possible to fit a semi-electric or fully electrical articulated ball head.

Brief component description
Alongside a microprocessor, the trailer module consists essentially of overload-resistant sense FET power circuit breakers for the trailer power circuits.
The sense outputs of the power circuit breakers enable monitoring of the power circuits for overload current or wire breaks. The power switches are activated via CAN messages.
Also implemented is an input for direct activation of the brake light by the brake light power circuit of the towing vehicle (hard-wired). The emergency function guarantees the function of the brake light on failure of the CAN bus.

The following control units are involved in the functions of the trailer module:
- AHM trailer module The trailer module controls and monitors the current circuits of the trailer. The trailer module also separates the load circuits of the trailer from the vehicle electrical system of the towing vehicle. In the event of system faults, the trailer module creates the Check Control messages.
- Control unit for the electric folding trailer tow hitch (E9x) The control unit is connected to the vehicle electrical system by a 16-pin connector. The control unit has no direct connection to the bus system. The electrical folding trailer tow hitch release is operated using a button in the luggage compartment. The control unit is installed in the luggage compartment in the equipment holder. The control unit is neither programmable nor self-diagnosable.
- Control unit for the fully automatic trailer tow hitch (E6x) The control unit is connected to the vehicle electrical system by a 16-pin connector and a 4-pin connector. The control unit has no direct connection to the bus system. The fully automatic trailer tow hitch is operated using a button in the luggage compartment. The control unit is installed in the luggage compartment in the equipment holder or in the spare wheel well. The control unit is neither programmable nor self-diagnosable.
- CAS: Car Access System The CAS control unit delivers the signal for terminal 15. This signal is connected at the control unit of the trailer tow hitch release.
- JBE: junction box electronics The junction box supplies the trailer module with voltage (terminal 30g). Moreover, the junction box also supplies the control unit of the trailer tow hitch release with voltage.

The trailer module detects overvoltage and undervoltage in the vehicle electrical system. Outside the valid range of 9 to 15 Volt, functions that are not relevant to safety are switched off. For example, the trailer tow hitch release cannot be activated with undervoltage or overvoltage.







System functions

The following functions are described:
- Trailer lighting
- Trailer detection
- Trailer tow hitch unlocking

Trailer lighting
The trailer lighting runs the following functions:
- Brake lamp
- Side lights / parking light
- Indicating, hazard warning flashers, crash alarm hazard warning flashers, DWA alarm flashing
- Rear foglamp
- Reversing lamps

The trailer module activates the individual lighting circuits of the trailer. The implemented functions for the trailer lighting are described in the following section.
- Brake light The brake light on the trailer is switched on when the service brake in the towing vehicle is operated.
- Side lights / parking light The side lights on the trailer are activated when the light switch on the towing vehicle is in the side lights or low-beam headlight position. When the Automatic Light Control is activated, the side lights of the trailer are switched on depending on the level of brightness.
- Indicating, hazard warning lights, crash alarm hazard warning lights, DWA alarm flashing For turn indicating, there are two indicating functions implemented by the trailer module.
- One-touch flashing: When the turn signal/high beam switch is touched briefly, the turn indicator bulbs are activated briefly. The number of flashing pulses here depends on the encoding of the towing vehicle.
- Continuous flashing: When the turn signal/high beam switch is 'overpressed' beyond the pressure point, the turn indicator bulbs are activated with the function "continuous flashing".

The flashing frequency is adapted to the flashing frequency of the towing vehicle by the trailer module. At the start of each flashing period, CAN messages are sent in cycles. These messages serve to synchronise the flashing frequency between the towing vehicle and trailer. If a turn indicator bulb on the vehicle or trailer is defective, the flashing frequency is doubled (defective flashing).

- Rear fog light: The rear fog light is switched on with
- terminal 15 ON and
- the light switch of the towing vehicle in the low beam position
- the rear fog light activated by the switch.
Or with
- terminal 15 ON and
- the light switch of the towing vehicle in 'side lights' position and
- the fog lights activated and
- the rear fog light activated by the switch.
The rear fog light is switched off again when
- the rear fog light is deactivated by the switch
- terminal 15 OFF, or
- light switch OFF.
- Reversing light The reversing light is switched on when reverse gear is engaged on the towing vehicle and terminal 15 is ON. The reversing lights are switched on with a delay of a fraction of a second to avoid their flashing during gear changes.

Trailer detection
The trailer module detects a trailer as connected when at least two loads (cold measurement) are detected at the lighting outputs. The trailer module then reports the status "Trailer connected". This status report is implemented in the towing vehicle in a number of control units. For example, the Park Distance Control is disabled at the rear. In vehicles built up to 2006, the reversing light and rear fog light of the towing vehicle are disabled for trailer towing.
In vehicles built after 2006, the reversing light is no longer disabled. If the rear fog light on the trailer fails, there is a switch to the rear fog light of the towing vehicle.

Electrical folding trailer tow hitch
The electrical folding trailer tow hitch is an element of the optional extra 'trailer tow hitch with articulated ball head'. This optional extra has been offered for the E9x since 03/2007. The electrical folding trailer tow hitch is operated using a button in the luggage compartment.







There is a two-colour LED for the indicator lamp in the button. The following signals are possible:
- The LED lights up green: the trailer coupling is in the locked end position.
- The LED flashes slowly red (2 Hz): the trailer coupling is not in the locked end position.
- The LED flashes quickly red (4 Hz):
- The drive has been activated for longer than 4 seconds.
- The current for the drive necessary for release has not been reached (12 Amperes).

The drive for the trailer tow hitch release is attached to the release unit. The ball head can only be released if the following conditions have been met:
- Terminal 15 OFF
- Luggage compartment lid open

The trailer tow hitch can be operated as of terminal 30 switched ON. The following signal states must be present:
- Terminal 30 switched: high signal
- Button for trailer tow hitch release: low signal
- Terminal 15: low signal
- Rear lid contact switch: low signal
- Micro-switch of trailer tow hitch release, output 1: low signal
- Micro-switch of trailer tow hitch release, output 2: high signal

After a successful check of the signal states, the direct current motor for the trailer tow hitch release is activated.







The drive for the trailer tow hitch release consists of a direct current motor and a reduction gear. The following components are integrated in the release unit:
- Micro-switch with slide and compression spring
- Drive disc for the micro-switch
- Drive disc for the release lever
- Release lever







Fully automatic trailer tow hitch E6x
The fully automatic trailer tow hitch is an element of the optional extra 'trailer tow hitch with articulated ball head'. This optional extra has been offered for the E6x since 03/2007. The fully electric trailer tow hitch is operated using a button in the luggage compartment.
There is a two-colour LED for the indicator lamp in the button. The following signals are possible:
- The LED lights up green:
Ball head locked in one of the 2 end positions and conditions required for switch-on met
- The LED flashes slowly green(2 Hz):
The ball head is in the locked end position ("pivoted out") and the trailer connector or an adapter is in the trailer socket.
- The LED lights up red:
There is undervoltage or overvoltage at the control unit for the fully automatic trailer hitch
- The LED flashes slowlyred (2 Hz):
Ball head in motion or not in a locked end position
- The LED flashes quickly red (4 Hz):
- Control unit for the fully automatic trailer hitch is not initialised
- Maximum current for activation has been exceeded. (obstacle or stiff movement in the mechanism)
- Control unit for the fully automatic trailer tow hitch is faulty

- The light-emitting diode is OFF:
- Conditions required for switch-on not met
- System not operational, e.g. due to blown fuse or broken lead

The trailer tow hitch can be operated as of terminal 30 switched ON. The following signal states must be present:
- Terminal 30g: high signal
- Button for trailer tow hitch release: low signal
- Terminal 15: low signal
- Rear lid contact switch: low signal

After a successful check of the signal states, the direct current motor for the trailer tow hitch release is activated.

Automatic pivoting out or in (single brief press of button)
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 can be halted at any time by briefly pressing the button a further time.

The operating function of the button is as follows (starting position: ball head pivoted in):
- Short press on button:
The ball head pivots out.
- Next press of button:
Pivoting of the ball head is halted immediately.
- Next press of button:
The ball head pivots in.
- Next press of button:
Pivoting of the ball head is halted immediately.
- Next press of button:
The ball head pivots out.
- etc.

Fully automatic pivoting out or in can only be started if the ball head is in one of the two end positions or fully automatic pivoting out or in has been halted by pressing the button.

Reversing the pivoting movement
If the permissible current consumption of the DC motor is exceeded during fully automatic pivoting out or in (e.g. as a result of an obstruction, stiff movement or low ambient temperatures), the control unit for the fully automatic trailer hitch triggers reversing. The ball head's pivoting movement is halted. The ball head is pivoted back a short way in the opposite direction (reversed). It can now only be moved by continuous operation of the button (manual operation). 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).

Pivoting out or in by continuous operation of button
This mode is initiated by operating the button for the fully automatic trailer hitch for longer than 1 second. The ball head only pivots for as long as the button is pressed. If the button is held pressed, the ball head is pivoted in the opposite of its previous direction of pivoting. The ball head's pivoting movement stops when the button is released. A further pivoting movement can only be performed in this mode. Increased current consumption by the DC motor is permissible in the continuous button-operated mode. If the current consumption permissible in this mode is exceeded, the ball head's pivoting movement stops. The ball head does not pivot in the opposite direction to its previous direction of pivoting (no reversing in this mode). Only if an end position is reached in this mode is automatic pivoting out or in possible again.

Fully automatic trailer tow hitchE70
The fully automatic trailer tow hitch is an element of the optional extra 'trailer tow hitch with articulated ball head'. This optional extra has been offered for the E70 since 09/2009. The fully electric trailer tow hitch is operated using a button in the luggage compartment.
There is a two-colour LED for the indicator lamp in the button. The following signals are possible:
- The LED lights up green:
Ball head locked in one of the 2 end positions and conditions required for switch-on met
- The LED flashes slowly green (2 Hz):
The ball head is in the locked end position ("pivoted out") and the trailer connector or an adapter is in the trailer socket.
- The LED lights up red:
There is undervoltage or overvoltage at the control unit for the fully automatic trailer hitch
- The LED flashes slowly red (2 Hz):
Ball head in motion or not in a locked end position
- The LED flashes quickly red (4 Hz):
- Control unit for the fully automatic trailer hitch is not initialised
- Maximum current for activation has been exceeded. (obstacle or stiff movement in the mechanism)
- Control unit for the fully automatic trailer tow hitch is faulty
- The light-emitting diode is OFF:
- Conditions required for switch-on not met
- System not operational, e.g. due to blown fuse or broken lead

For the fully automatic trailer hitch to pivot out and in, the following conditions required for switch-on must be met:
- Terminal 30B ON
- Luggage compartment lid open
- Range close to stationary
- Valid speed signal
- Trailer connector not plugged into the trailer socket (only with ball head articulated outwards)
- No overvoltage or undervoltage in the vehicle voltage

The system, with ignition switched off is disabled after no later than 2 minutes. (LED goes out). In order to reactivate the system either:
- close the boot lid or doors and open them again
- Switch on the ignition
- press the 'Open central locking' button on the master key

The control unit for the fully automatic trailer hitch uses the signal states to check whether the pivoting movement can be started. If the conditions required for switch-on are met, the following procedures can be performed by pressing the button for fully automatic trailer hitch:
Automatic pivoting out or in (single brief press of button)
Briefly pressing the button (for less than 1 second) pivots the ball head fully automatically from one end position to the other. Only press the button for starting the automatic pivoting of the ball head briefly (not longer than 1 second). During the first 5-7 seconds, the system unlocks the ball head and, initially, there is no visible movement from the ball head. Then the ball head moves into its end position and is relocked (approx. 5-7 seconds). The LED flashes red during this process at 2 Hz.
Fully automatic pivoting out or in can only be started if the ball head is in one of the two end positions or fully automatic pivoting out or in has been halted by pressing the button.
During the automatic pivot movement of the ball head, no mechanical forces must be exerted on the ball head.
- Before starting, first ensure that the movement range of the ball head is free of obstructions
- In particular, ensure that no manual movement is applied to the ball head during the unlocking and locking process caused by an external factor (blows, kicks).

Reversing the pivoting movement
If the permissible current consumption of the DC motor is exceeded during fully automatic pivoting out or in (e.g. as a result of an obstruction, stiff movement or low ambient temperatures), the control unit for the fully automatic trailer hitch triggers reversing. The ball head's pivoting movement is halted. The ball head is pivoted back a short way in the opposite direction (reversed). 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).

Pivoting out or in by continuous operation of button
This mode is initiated by operating the button for the fully automatic trailer hitch for longer than 1 second. The ball head only pivots for as long as the button is pressed. If the button is held pressed, the ball head is pivoted in the opposite of its previous direction of pivoting. The ball head's pivoting movement stops when the button is released. A further pivoting movement can only be performed in this mode. Increased current consumption by the DC motor is permissible in the continuous button-operated mode. Never move the ball head into its end position by means of mechanical pivoting. If the current consumption permissible in this mode is exceeded, the ball head's pivoting movement stops. The ball head does not pivot in the opposite direction to its previous direction of pivoting (no reversing in this mode). Only if an end position is reached in this mode is automatic pivoting out or in possible again.

Notes for Service department

Diagnosis instructions for the trailer module
The trailer module detects and reacts to the following faults:
- Checksum error of the various memories and watchdog reset
- Faults of the CAN drivers
- Line faults of the CAN interface and of the brake light input
- Line fault of all outputs with short circuit and wire break
- Undervoltage / overvoltage and implausibility of the control unit voltage in comparison with the vehicle voltage
- Implausibility of a CAN message "Braking" compared to the hard-wired brake light input at the control unit
- Implausibility of the sense values of the lighting outputs of the control unit
- Faults on the lamp outputs of the trailer module are output as Check Control messages

Notes on trailer tow hitch release
For a more detailed description of the trailer tow hitch release, see: SBT 610804120.

Notes on encoding/programming
After installation of a trailer module, the control unit must be recoded. In doing so, observe the various national versions.
Not responsible for printing errors, mistakes and technical changes.