We have a 1992 E30 convertible and the passenger door has stopped working ( won't lock, open, or close without undue manipulation ). Is also effecting the ability to lock the drivers door and trunk, usually activating either of those would lock/unlock the others. Any thoughts?
Sounds like the lock actuator may have failed. They can cause the whole system to fail sometimes until it is repaired. I would start with that and inspect the actuator to makes sure none of the linkage or lock is damaged.
Check the GM5 module. This controls the unlocking functions of the doors. Your passenger door fails first, then the drivers door. It's an easy and inexpensive fix. On my Z4, the GM5 is located behind the glove box.
