On my X5 there is an evap solenoid on the right head, front of the block, (drivers side). The valve inside gets sticky. Every so often, I remove it and give it a shot of lubrication. I apply 12 volts to the solenoid "directly" a few times to cycle it. It is usually good for a year or so then it sticks again. The DTC is 0443. This can be read with an obd2 scan tool.