Window drop failure
The soft-top on this 2001 BMW 318Ci has a lip around the top of the door’s drop glass to ensure it is as weatherproof as possible. When the car’s designers introduced this feature they realised it could cause a problem with the glass catching the roof as the door was opened and closed. As a result, they introduced a clever addition to the window motor that would drop the glass fractionally when the door handle was pulled, then close it up again when shut.
This system relies on a small microswitch built into the door lock. However, this feature was not working on this BMW because of a failed microswitch. Unfortunately for the owner, spraying the switch with electrical cleaner had no effect, so we fitted a complete new lock (£140), which remedied the problem.