L322 Range Rover System Description and Operation
LIGHTING
DESCRIPTION AND OPERATION 86-2-11
Circuit Protection
Operation of the lamps is performed using overload proof Metal Oxide Semiconductor Field Effect Transistors
(MOSFETs). The MOSFETs have a diagnostic output for bulb monitoring and can detect overload, load interruption
with the lamps switched on and short circuit to positive with the lamps switched off.
The MOSFETs are protected against short circuits, removing the requirement for the lamps circuits to be protected
by fuses. The MOSFETs respond to heat generated by increased current flow caused by a short circuit. Normally this
would cause the fuse to blow. The MOSFETs react to the heat increase and cut the supply to the affected circuit. Once
the fault has been rectified or the MOSFET has cooled, the MOSFET will automatically reset and operate the circuit
normally.
If an overload occurs, the current flow is dependant on the temperature of the related MOSFET and can be up to 20
times the rated current of the lamp. The MOSFET heats up and deactivates the load applied to the circuit. When the
MOSFET cools the circuit is once again reactivated. This thermal cycling occurs continuously in the event of an
overload occurring.
The brake switch is also monitored by the LCM. If the LCM detects a short circuit to ground in the switch circuit it
activates messages to the driver in the message centre. These messages will display switch defective and LH and
RH stop lamp defective. The brake switch is also monitored when the ignition is in position II. The LCM checks the
acceleration speed of the vehicle (via bus messages). If the vehicle is accelerating and the brake switch is still active
after 10 seconds, the LCM starts a timer. If, after 2 minutes, the brake switch is still active and the vehicle is moving,
the LCM activates defective switch messages in the instrument pack message centre.
18
Front LH side lamp
Output
19
Hazard warning switch lamp
Output
20 to 23
Not used
–
24
Engine coolant level sensor
Input
25
Brake switch
Input
26
Reverse gear selected
Output
27
Headlamp levelling vertical aim control
Output
28
Reverse gear selected
Output
29
Illumination dimmer switch supply
Output
30
Steering column lighting switch (left and right turn selections)
Input
31
Ignition power supply
Input
32
Not used
–
33
Lighting switch headlamp selection
Input
34
Not used
–
35
Trailer module serial interface
Input/Output
36
I bus
Input/Output
37 and 38
Not used
–
39
Reverse gear selected
Output
40
Not used
–
41
Brake fluid level switch
Input
42 to 44
Not used
–
45
Rear fog guard lamp switch
Input
46
Not used
–
47
HDC active signal
Input
48 and 49
Not used
–
50
Steering column lighting switch, main/dipped beam and flash
selection
Input
51
Lighting switch side lamp selection
Input
52
Lighting switch ground
–
53 and 54
Not used
–
Pin No.
Description
Input/Output