Lamp Control Module: Description and Operation
Lamp Control Module (LKM)"
Functional Description:
General:
The lamp control module (LKM) contains the relays for
- Low beam
- Fog lights
The tail lights, parking lights, brake lights, rear fog lights and license plate lights are not switched on by the LKM but directly by the switches.
The LKM monitors the power circuit of the lamps, several fuses, the function of the brake light switch, the pop-up headlights and the function of the relays contained in the LKM (see scope of monitoring).
If one of the components included in the scope of monitoring is found to be defective, this is indicated by way of a corresponding message in the multi-information display (MID) and stored in the defect code memory of the LKM.
Activating control unit:
The LKM is activated by the I-bus. The I-bus is active under the following conditions:
- as of ignition switch position 1 (terminal "R" ON)
- or pressing an MID button
- or opening the driver's door
Deactivating control unit:
The LKM switches off under the following conditions:
- ignition switch in position "0", ignition key removed in USA version
- and the driver's door closed for 2 minutes or the closed driver's door opened and closed once
The I-bus is a data link to the EMK and can be tested by way of the diagnostic program belonging to this system.
Voltage supply:
Complete operation of the LKM control unit is only guarantied at a supply voltage of minimum 9 V to maximum 18 V. The supply voltage is monitored at the control unit connector X12 (A/white) Pin 20.
Monitoring is restricted if the LKM detects a supply voltage above 18 V Data telegrams are no longer sent at a voltage below 9 V ( *D* Data transfer defective).
Monitoring:
Type of monitoring:
The LKM differentiates between so-called hot and cold monitoring.
Hot monitoring: The power circuit is checked when the component is switched on.
Cold monitoring: The power circuit is checked when the component is switched off.
Scope of monitoring:
The scope of monitoring depends on the country variant of the LKM. The LKM takes into consideration additional power circuits or power circuits which are not installed for the relevant country variant
Component Type of monitoring
Left/right low beam hot/cold
Left/right parking light hot/cold
Parking light fuses and parking light
switch function are also monitored
Left/right tail light hot/cold
(on the outside)
Left/right tail light not monitored
(on rear lid)
Left/right fog light hot/cold
Left/right license plate light hot
Left/right rear fog light hot/cold
Left/right/centre brake light hot/cold
Fog light fuse hot/cold
Fuse for all fog lights and low hot/cold
beam/high beam control circuit When the ignition switch is in position
"2" (terminal 15 ON).
Brake light fuse hot/cold
When the ignition switch is in position
"1" (terminal RON).
Low beam relay hot/cold
Fog light relay hot/cold
Right/left pop-up during closing/opening or when opened
headlight /closed
Brake light switch hot
When at least one brake light is okay.
Brake light:
The brake light test switch is used to monitor operation of the brake light switch. A corresponding error message appears in the MID when the LKM detects brake light test switch ON and brake light switch OFF. The function is OK. for LKM monitoring if the LKM detects brake light test switch oft and brake light switch ON.
Monitoring the function of the brake light switch is based on the assumption that at least one brake light is OK. It is therefore possible to close the power circuit.
Depending on the country variant, the left, right and centre brake lights are monitored by the LKM. The brake lights are activated directly by the brake light switch and routed via the LKM for monitoring. For safety reasons, they are not controlled by the LKM or a relay incorporated in the LKM.
Relays:
The LKM controls the power circuits for the fog lights and low beam lights by way of two relays incorporated in the LKM. The low beam relay can be switched by the light switch or by the control unit. This interlinking ensures that the low beam relay can still be switched even in the event of failure of the control unit electronics.
The relays contained in the LKM are monitored as to whether they switch on the load circuit when they are activated and switch off the load circuit when they are not activated (sticking relay).
In order to switch the power circuit for the pop-up headlights and high beam/headlight flasher lamps, the LKM drives two double relays which are not accommodated in the LKM. The pop-up headlight relays are powered with 12 V and the high beam/headlight flasher relays with 5 V.
Headlight/headlight flasher:
The function for high beam and headlight flasher differs depending on the country variant of the LKM (see country variants). In the ECE basic version, the high beam lamps in the pop-up headlights can be switched on together with the headlight flasher lamps in the lamp assembly. The prerequisite for switching on the high beam in the pop-up headlight is that the pop-up headlight is open.
Pop-up headlights:
The pop-up headlights are opened when the LKM determines that the low beam or the fog lights are switched on. The LKM detects the position of the pop-up headlight motor by means of limit switches integrated in the motor.
If the pop-up headlights are switched on and off again more than 10 times within 1 minute, they remain in the open position at the tenth time.
If the LKM detects that the pop-up headlights are blocked, the LKM only permits the headlights to be switched on and off 3 times within one minute.
A pop-up headlight is considered as being blocked when it is driven for longer than 5 5 by the pop-up headlight relay in the LKM and the LKM does not receive a signal from one of the limit switches (pop-up headlight open/pop-up headlight closed).
If, during activation, only one limit switch is detected, the time is measured till the one limit switch is detected once again. This time is halved and the pop-up headlight motor is activated for this time. This emergency function positions the pop-up headlights with a sufficient degree of accuracy.
The pop-up headlights can also be opened by hand in the event of failure of the control unit electronics or of the pop-up headlight relay.
Country variant:
The country variant of the LKM can be read out via the BMW diagnostic system. At present, the LKM distinguishes between the following variants.
*D* Display Scope of function
ECE Basic version
Scandinavia as ECE, but only one rear fog light on the left
Norway Norway as Scandinavia, but the fog lights can only be
switched on with the low beam and high beam switched off.
Australia as ECE, but with an additional third brake light
USA as ECE, but with additional third brake light, no rear
fog light and deviating high beam/headlight flasher
function with headlights in open position (only the high
beam lamps light in the pop-up headlights).