Power locks - 1998 Trans Sport

Just bought a 98 Trans sport Montana. The power lock system is not working properly. You can "Unlock" all doors using the drivers switch and unlock each individual door by using its switch.Howeverm you can not "Lock" any door using any of the door switch's!!! I believe it may be a defective Body Control Module which is the module that my manual says controls the lock system. Does anyone know ehere this module is located???

Please respond to: [email protected]

Thanks

Rick S