How do you replace a parking sensor on a 2003 BMW 325i tourer . One of the 4 sensors does not click. How is it fixed into the trim? Do you have to remove the bumper trim. How long is the lead and where does it plug in to the car's wiring. Do you need any trim clips or anything which is likely to require replacement appart from the sensor?

I've now managed to remove it, put some WD40 on the plug contacts replace it & it's working. For the benefit of others It helps to see a photo of one on E-Bay so you know what you are dealing with.
The sensor was held into the trim largely by friction (& Dirt) and a small clip which latches over a lug on the cylindrical body. Push this clip away from the sensor and firmly push in on the sensor until it comes out of the trim and can be withdrawn from the back. This is far more difficult than it sounds as the sensor is tight in the hole in the trim. Once it starts moving a bit use some WD40 & push it in & out to help free it. When it's dangling down the back of the trim use a small screwdiver to unlatch the 3-pin plug which engages the socket on the back of the sender and spray some WD40 on pins & socket engage & disengage plug a few times & with luck it will clean up & start working like mine did. No need to remove trim but small hands help. My car has the detachable trailer hitch so removal or the hitch panel in the trim helps access to the 2 middle sensors. I've now managed to remove it, put some WD40 on the plug contacts replace it & it's working. For the benefit of others It helps to see a photo of one on E-Bay so you know what you are dealing with. The sensor was held into the trim largely by friction (& Dirt) and a small clip which latches over a lug on the cylindrical body. Push this clip away from the sensor and firmly push in on the sensor until it comes out of the trim and can be withdrawn from the back. This is far more difficult than it sounds as the sensor is tight in the hole in the trim. Once it starts moving a bit use some WD40 & push it in & out to help free it. When it's dangling down the back of the trim use a small screwdiver to unlatch the 3-pin plug which engages the socket on the back of the sender and spray some WD40 on pins & socket engage & disengage plug a few times & with luck it will clean up & start working like mine did. No need to remove trim but small hands help. My car has the detachable trailer hitch so removal or the hitch panel in the trim helps access to the 2 middle sensors.