The BMW factory installed amplifier, as included in the E90/92 models, supplies a boosted stereo signal to the vehicle's stereo sound system. A stronger signal means a louder system and a clearer performance by the stock head unit. BMW owners who wish to disconnect the amplifier from the stereo sound system can choose to have the amp disconnected by a professional car audio technician. To save the cost of labour, you can locate and disconnect the amp yourself.
Lift the BMW's bonnet and loosen the bolt that holds the grounding cable to the negative battery terminal post with a 10mm wrench. Lift the cable from the battery and set it aside.
Open the boot. Remove the three plastic fasteners that hold the carpet panel of the boot on the driver's side to the side of the cargo area with a flathead screwdriver. Remove the metal tie-down located on the bottom of the panel with a Torx T-40 socket and drive.
Remove the plastic caps from the top side of the plastic panel at the back edge of the boot with a flathead screwdriver or trim panel removal tool. Pry the plastic fasteners from the panel inside the boot. Remove the two screws under the upward facing plastic taps with a Phillips-head screwdriver.
Remove the plastic panel at the back of the boot by hand. Pull the carpeted side panel from the side of the boot to expose the factory amplifier. Unplug the multicoloured wiring connector from the signal outlet on the side of the amplifier. Unplug the black power supply cable from the outlet labelled "Power In" on the amplifier.