pilot bush

I see a few posts about replacing a leaking pilot bush, which along with a duff battery, can cause the P2600 fault code to appear and put the car in to limp mode. But, what does the pilot bush actually do ? I maybe thick, but a quick learner :-) Richard

Could someone please clarify the Pilot Bush for me? I have a 2000 w202 c class 200T with the 722.6 automatic gearbox in it. I have recently bought the car and the gearbox was clunky so I decided to change the transmission fluid and filter, I drained 2.5ltrs of black fluid from the box ...