Q: door locks on 1999 Mercedes-Benz ML430

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the doors are not locking i thought it was the relay changed the relay and the problem still exists someone told me it could be the module but i dont know where this module is located or if this is the problem please help
(2) Answers
The best way to really zero in on this problem is to scan the module that controls the door locks. It could be a switch, a module, a faulty door lock motor etc. A good Mercedes Tech should be able to zero in on this issue in less than an hour of shop time. You can go to a good independent Mercedes shop.

before replacing the module, have the system scanned. $1400 is an expensive 'dart' to throw if you are wrong. Can you lock the door lock from the inside? This is 1 way to eliminate the key factor. If you can't lock the doors from the inside with them all closed, it is doubtful it is the key. On Mercedes, the Master is the Trunk/rear hatch lock. Try your key in that, see if it either opens or locks the locks. This is 1 key test.
Also hitting the remote lock or unlock buttons on the key is another.
it can be the key, but as I just found out it was the module in the fuse box in the engine compartment water got into the fuse box $1400 plus tax installed