Land rover horn beeps twice after locking doors

SOURCE: Central locking issue on my Land Rover Discovery II 2003

Does it open from the outside once you have manually opened it from the inside.

SOURCE: land rover discovery central locking.

No, likely to be caused by the actuators in the lock mechanism failing usually causing the door to remain locked. The boor door can also fail this way, as do the front side doors. Replacement requires the whole lock unit to be replaced at a cost of roughly £60 a lock, and a hours work. Helps if you have small hands. Requires a full strip down of the door and you will need the lock unit, trim clips (a few quid) and a trim removal tool (tenner). You can bodge with a flat head screwdriver, but the tool does help prevent damage to the clips & trim panel.

SOURCE: 2003 range rover power door locks do not work...

does the roof lamp work? if not then means your Vehicle in transport mode. to have it in normal mode you need to take it to a dealer or something equivalent to have the job done by approved diag. machine

SOURCE: How to repair the door locks on a 1997 Land Rover

Try this, Download FREE RAVE manual and this is service manuals for almost every Rover - http://www.landroverresource.com/ (You'll find your answer ti that and just about anything to do with your Disco)

SOURCE: RADIO CODES FOR A 2003 LAND ROVER DISCOVERY

It is usually listed in the top section of repair invoices from a dealership.
If you still cannot get the code. there are many sites on the internet that can
supply the code for a fee.