In order to replace the latch on an Audi A4, remove the door trim panel and watershield and first close the window. Then remove the window regulator carrier out of the door whereby in some early models with no anti-theft panel this step might not be required. Assuming they are there, unclips and removes the anti-theft panel to the lock. Note the positions of the locking button, exterior handle, and lock cylinder operating rods and carefully install them back in the lock mechanism. Unscrew the two holding screws and pull the lock unit with its base plate out of the door by disattaching the vacuum hose attached to the central locking actuator. Disconnect the interior handle operation cable with the lock unit and de-plug the switch wiring. The vacuum actuator unit can be unscrewed and the locking tab depressed to be taken off, and then it should be reassembled in the same order. In the case of the Volkswagen Passat, the door trim panel is the first to be removed, since the door latch, radio speaker, and window regulator are all connected to a large metal carrier which is best removed as a single unit. Once the lock cylinder and handle are removed, loosen up the glass track bolts by removing the window glass, and then tape the glass in the UP position, after removing it off the regulator. Unplug the electrical harness of the door and take out the window regulator carrier. Removal is by prying out the two pins and reversing the latch and reconnecting the cable and linkage rod, but the process of installation is the opposite. In the case of the lock cylinder in Audi A4, the exterior door handle is to be removed and the wiring which leads to the central locking switch to be unplugged. To replace the lock cylinder, remove the lock cylinder housing out of the door, then insert the key to take the circlip and slide the driver plate and the spring off and then pull out the lock cylinder. To install a new lock cylinder, only to install it, it is necessary to put the parts in the housing, insert the new lock cylinder and then turn it on with the key and put the pieces back. In the case of Volkswagen Passat, take out the plastic plug of the latch end of the door, loosen the setscrew of the lock cylinder, and remove the lock cylinder. The process of removal is opposite to installation. In the case of the outer handle on the Audi A4, roll up the window and take out the door trim panel and watershield and the carrier of the window part. To unlock the locking element of the handle and lock cylinder, rotate the locking element to release it, remover the retaining screw and remove the handle assembly holding the outside handle trim in place. A small flat-bladed screwdriver may be used to remove the locking bar in case it is necessary. Removal is the opposite of installation. In the case of Volkswagen Passat, the lock cylinder should be removed, then the cable should be unclipped and the key-end of the handle should be swung back and out of the door and then the process will be the same with attaching it to the door.