Low levels or low pressure? Or you mean low enough levels to affect the pump suction / pressure or temperatures?
A low oil level is a signal to go check it on the stick to confirm that, not immediately shut down the engine. Many ways to go from there like add oil, check is it low due to normal consumption or is the loss big and unexpected, is there an external leak? Did someone forget to lock the drain valve closed? Did someone fit a spinner filter and connect it with hoses that are hidden below the deck plates and never get inspected and got hard and deteriorated and blew out and pumped “a bit” of oil out of the sump? There may be additional clues as you head down the ladder, like sickening smell or low oil pressure alarms or possibly shut down. Such is life.
On an EMD the oil level is always below the crankshaft. The p-pipes deliver oil to the piston crown “shaker” area for cooling and to lubricate the wrist pin bearing, thence to the cylinder and down to the sump.