2018 BMW 4 Series Reliability Report

These reports are a mix. Coolant leaks from a cracked oil filter housing or plastic vent lines show up repeatedly, sometimes coming back after a repair. Doors unlatch and swing open while driving. The power trunk closes on its own, and in one report it injured an arm. Sunroof glass shatters, and the panoramic roof shade sags into the cabin. Owners also report a failing emergency call backup battery, weak blind spot and cross-traffic alerts, and a vinegar smell from the air conditioning. One crash involves sudden acceleration at under 17,000 miles.

False seat belt warnings and the "Passenger Restraint System Malfunction" message account for most of these reports. Chimes sound for empty seats or for belts that are already buckled. The warnings come and go, sometimes in damp weather, and return after repairs. Dealers blame the passenger seat sensor mat, and owners report repair quotes of more than two thousand dollars. A smaller group describes mechanical faults: driver belts that won't retract, a rear belt that won't latch, and a belt that locked and unlocked over and over during a crash.

Coolant leaks lead to overheating, stalling, or lost power while driving. Water pumps fail, sometimes twice on the same car. Coolant hoses and the cylinder head vent line leak, and owners have to keep topping off the reservoir. Warnings like "Drive Moderately" or "Vehicle Will Shut Off" appear before the car loses power, and one report describes smoke filling the cabin. Failures appear between 49,000 and 105,000 miles. Some repairs uncover oil mixing into the coolant or further leaks at the oil housing.

Stalling is the common thread. The engine cuts out at stops or at highway speed, often with a "Drivetrain Malfunction" message. The causes reported include a failed fuel pump and fuel rail, a VANOS fault, and ongoing coolant leaks that bring jerking. Two crash reports describe the car surging out of control, and one left the driver with a fractured back. In another case a service check found a cracked driveshaft flex disc at 22,000 miles.

Faulty seat occupancy sensors trigger the restraint system warning here too. Dealers call for a new passenger seat mat, with one quote above two thousand dollars. Some technicians blame moisture, and owners who found no sign of it dispute that. Other reports describe lumbar support inflating on its own while driving and a driver's seat that slides under braking. In one reversing crash, the driver's seat collapsed backward and the driver suffered serious neck injuries.

Sunroof glass shatters without warning at highway speed, with a loud bang and glass landing on the shade. Front doors also open by themselves while the car is moving, at speeds as low as 15 to 20 mph. Some owners say no warning came until the door was already open, and one reports it happening twice. The remaining crash report concerns ordinary collision damage, not a defect.

Sudden unintended acceleration while parking caused two of the crashes reported here, and the cars struck other vehicles or objects. In another report, the cruise control rocker switch sticks and the car keeps speeding up past 80 mph. A run-flat tire blowout on the freeway also appears here. The car shook hard and pulled to one side instead of staying drivable, and it had to be towed.