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