I've been tracking down a parasitic current draw on my 2004 X350 3.5 V8 and it seemed to come from the front electronic module. I replaced both front and rear modules with a used pair without any reprogramming.
Somehow I now seem to be out of sink with the alarm. The car was double locked with the mirrors folded. As soon as I reconnect the battery, the alarm chirps and then goes off. If I turn the ignition to position 2 or even try to lock/unlock the drivers door the alarm still continues!! The key fob locked the car but seems not to unlock it now.
I have replaced the modules with the original ones and the problem still persists.
Is there any way to turn off/reset the alarm please before I drive my neighbours mad? A specialist thinks the car "thinks" it is being stolen.
All advice kindly received. Many thanks, Philippe

 

Very odd mine always turns of with the turn off ignition. Maybe try putting the key in the trunk key hole and open.

 

Start at the rear module. Place the original back in, don't try programming it. Unplug the horn or remove the fuse.

 

How would you install the used replacement rear ECU and resolve this alarm activation problem? I have this problem as I was trying to replace the rear ECU to try to resolve a parking sensor problem. The used ECU would allow me to lock the car, but not to unlock it and I had to use the key to open the boot to disconnect the battery and replace the new (used) ECU with the original rear ECU, after which I could unlock the car, but if I try to install the new (used) rear ECU now, it immediately triggers the horn alarm..... Would be grateful for any step by step recommendations. Thanks

 

Number on the module the same?
had that too . Had to unplug the horns on 2007 tdvi xj6 while honking

 

The X350 I gave to my stepson 2 years ago is still operational.
I still have a hand in its maintenance from time to time.
Not long ago he had the occasional alarm triggered for no good reason.
We removed the alarm speaker under the rear wheel arch.
However, as far as we can tell the main horn up front is still switched on by the alarm.
My guess is the wire to that horn may be spliced so it is operated by either the steering wheel or the alarm circuit.
If that is true finding the splice and disconnecting the alarm would be a bonus. I doubt anyone is seriously interested in stealing a 2003 X350 even if it looks much younger than its age and quite an expensive automobile.
For insurance purposes or for a mandated roadworthy check etc., the splice removal needs be reversible.

If the splice is an "electronic" splice within a module that would not be so easy to find and fix.
Depends on how it is done. If somebody sent me a module and I had the external wiring connections I might be able to doctor it.

 

Yup, same part number, but it was from the USA (I'm in Singapore) so it was configured differently. When I fitted it to the car, I checked the locking system..... and it then wouldn't unlock.... so I had to use the manual key to open up the boot and that triggered the alarm... so I had to quickly put back the original rear ECU to unlock the car, but I would like to put in a different ECU to check why my reverse sensors are having strange problems. They work when I start up the car, but at the end of the drive, they become continuously on. Then If I shut off the car and then turn the ignition key to on and put it in reverse, without starting the car, they work, but if I start the car, they become continuously on again.... Most irritating.... I've tried swopping multiple reverse sensor ECU's and it's still like that. When I checked with the Jag SDD, it gives me some errors in the rear body ECU, which are not correct (eg says reverse light on one side not working, but when I checked, they're ok) so I'm thinking that the problem may be with the rear body ECU, but now my spare automatically triggers the alarm when I plug it in. I'm going to try to remove the horn fuse and then reprogramme the rear body ECU this weekend to see it that gives me back a functionally correct rear body ECU.