Right, lets get this little thread starightened out.
The self leveling has 5 main components
A front mounted level sensor
A rear mounted level sensor
A near side level motor
An offseide level motor
A controller
The front mounted level sensor is on the lower front wishbone behind the front wheel passenger side wheel (towards the rear of the wheel arch)
The rear mounted level sensor is on the passenger rear semi trailing arm, this is just in front of the rear wheel
The level motors clip into the head lamps
The ECU is uder the passenger front wing on most mdoels.
The most common failure is the arm on the sensors popping out. This is almost always due to the connecting rod, which has 2 small ball joints on it' seizing up. This can often be fixed by replacing or freeing up the seized rod assemblies and re-connecting the arm to the sensors.
Less common is failure of the level motors, normaly following water ingress.
Tech2 will reveal the item at fault by reading the fault codes.