Why does the BMW 3 Series B48 always show insufficient coolant?

[DelJace]

It could be a leakage issue or a false alarm. Leakage scenarios: Internal engine leakage, usually caused by communication between the cylinder gasket and cylinder block. Coolant leaking externally is typically due to pipe joint leaks, radiator seepage, poor sealing of the radiator cap, or damage to the radiator cap's air valve. Insufficient coolant can lead to poor engine cooling and cause damage to the engine. False alarm scenarios: The coolant is too clean, and the level sensor cannot detect it. In this case, you can add some tap water with a small amount of dissolved salt (do not pour in the undissolved part at the bottom). There might be a fault with the liquid level sensor or its control wiring harness, such as contact failure at the coolant level switch connection or interruption at the wiring harness contacts.