Direction indicator lamp failure detection

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Land Rover Discovery, 2003 Land Rover Discovery, 2002 Land Rover Discovery, 2001 Land Rover Discovery, and 2000 Land Rover Discovery. However, it is still accessible from the selected car via links, so may be relevant.

The BCU uses the following logic inputs to determine if there is a direction indicator bulb failure or if the presence of a trailer is detected. The BCU uses the information to decide which output to enable at any particular instance:

Right direction indicators requested.
Left direction indicators requested.
RH indicators current sense.
LH indicators current sense.

If a direction indicator bulb failure or a trailer presence is detected, the following outputs can be generated depending on the BCU logic states:

Trailer detected.
Bulb failure detected.
Direction indicator short circuit.
Direction indicator relay stuck.

The BCU can be configured whether or not to provide bulb failure warnings.

When the direction indicators are operating, instrument pack direction indicators flash in sequence with the exterior direction indicators. If a failure of an indicator bulb occurs, the corresponding instrument pack indication lamp will flash quickly to warn of the problem.

The IDM monitors the current drawn through the circuit to detect for the occurrence of a lamp failure. If an indicator lamp fails, the IDM detects the drop in current drawn through the resistor and operates the indicator relay at a faster speed. The fast flash is demonstrated on the instrument pack direction indicator warning lamps to bring attention to the driver that a direction indicator bulb failure has occurred. The current sense for the related indicator lamps (RH or LH) are checked when a direction indicator request has been made that lasts for at least 160 ms. The current level sensed is relative to the number of working bulbs and determines the request generated by the BCU.

NUMBER OF WORKING BULBS

Number of working bulbs	Request generated
3	Trailer detected
2	None (bulbs okay)
1	Bulb failure detected
0	Direction indicator short circuit detected

The output is signalled to the instrument pack using the serial communications link. If the hazard warning lamps are operating, both sets of direction indicators are checked using the current sensing functions to check the number of bulbs on each side of the vehicle.

If the BCU detects that a direction indicator request has not been made, but one or other of the current sense inputs indicate that current is flowing, a 'Relay stuck' output is generated.