What this covers
Our repair data ties the B46 and B48 to the 330i, 430i, 230i, 530i and the X3 and X4 xDrive30i. The engine page is BMW B46/B48 engine. The numbers here are what owners reported, not failure rates.
Cooling: pump and turbo coolant line
A coolant leak at the front of the engine is the first place to look. On the B48 one BMW tech recommends replacing the full pump and bracket assembly because the bracket gasket can leak, while another says to replace only the cracked part. See Water Pump (N20 / B46 / B48).
The turbo coolant return line usually leaks at its rubber section or connections, with slow coolant loss and crusty residue around the turbo lines. The feed line sits on top and has to come out first, and several cups of coolant spill when the line comes off at the thermostat end. One DIYer bought the O-rings from a dealer for a small sum. See B46/B48 Turbo Coolant Return Line.
The plastic oil filter housing
The B58 and some B48 cars share the plastic oil filter housing that cracks and leaks coolant or oil. Book time quoted in the source threads is about five hours, but some shops billed 10 to 12.5, and many quotes add the heat management module, hoses or the water pump. Compare like for like. See B58 / B48 Oil Filter Housing (Coolant Leak).
Fuel pump and ignition
The in-tank low pressure pump is a known cause of a drivetrain malfunction warning, loss of power and stalling on B46 and B48 cars, often at low fuel. California and other CARB-state cars may get it covered under the emissions warranty. See Low Pressure Fuel Pump (In-Tank).
Spark plugs are the scheduled item; coils only need replacing if they fail or test bad. Dealer plug quotes around a thousand are common, so get an independent quote for comparison (Spark Plugs & Ignition Coils (B58 / B48)).
Service costs and the X3
Four-cylinder cars often qualify for BMW Value Service oil pricing at participating dealers once the free maintenance period ends, which is much lower than the standard menu. Confirm the oil spec for your engine (Oil Change / Oil Service). On the G01 X3, rear differential axle seals are a reported seep (G01 X3 Rear Differential Axle Seals); see the BMW X3 G01 Buying Guide: What It Costs to Fix for the full list.