What does the yellow oil lamp mean on a 1999 BMW 328I?

The yellow oil lamp on a 1999 BMW 328i indicates low oil pressure. When the oil pressure is low, the oil pump cannot adequately lubricate the engine, which can cause serious engine damage. If the yellow oil lamp illuminates while you're driving, pull over and turn off the engine as soon as it's safe to do so. Check the oil level and add oil if necessary. If the oil level is full, have the vehicle towed to a mechanic to diagnose and repair the cause of the low oil pressure.