2019 BMW 4 Series Reliability Report

A "Passenger restraint system malfunction" or "Air Bag Off" warning is the dominant complaint, sometimes traced to the seat occupancy sensor. Dealers say the air bags may not deploy while the warning is on. Repairs have included a new seat and mat, a knee air bag wiring harness, or the air bag control unit, and owners say dealers often refuse to cover the work under warranty. Crash reports describe air bags failing to deploy, frontal bags staying off when side bags fired, and facial cuts from a deploying bag.

Coolant leaks lead to overheating, low-coolant warnings, and in some cases limited speed or a stall in traffic. Reported sources include leaking water pump seals, plastic hoses and fittings, a coolant vent line, and a cracked oil filter housing that later triggers low oil warnings. One plastic-part failure came at 35,000 miles. A failed pressure control valve causes a loud high-pitched noise and white exhaust smoke, with stalling and jerking afterward. One car caught fire under the hood at 15 mph with only 4,500 miles, cause undetermined. Excessive oil consumption also appears.

The brakes fail to stop the car, and three of these reports end in crashes. Emergency brake assist sometimes takes no action before a low-speed collision. Elsewhere it slams on without cause, sometimes after a loud screeching alarm, then fails to react when the car approaches obstacles. One brake failure came with an Electronic Stability Control malfunction message and an abnormal noise. Another describes the engine racing to full RPM while the brakes were fully applied. Dealers have not pinned down a cause in these cases.

Condensation and pooled water build up inside the headlights after rain or in cold weather, dimming the light and throwing the beam off angle. Owners say dealers call it a known issue but decline warranty coverage, and one replacement quote reached 4.5K. A second problem is the daytime running light module overheating and melting the light tube. The tube is sold only as part of the full assembly, quoted at $4000-6000 per side, and the failure can fail a state inspection.

At highway speed the car slows sharply on its own, dropping from 60-65 to 35-40 mph in one case, and the accelerator stops responding. Drivers describe coasting through traffic with nowhere to pull over and no warning light. A separate report describes the screen blacking out at startup and the car then accelerating without pedal input, more than once. Dealer tests have not found the cause, so these remain intermittent, unresolved loss-of-control events.

Power steering assist cuts out at startup, triggering DSC and steering lights, an increased steering effort warning, and a cascade of disabled driver aids. Other reports describe the steering wheel locking and the car veering toward oncoming traffic, even after a dealer visit. There is also a report of the car dying on a busy road, which the owner tied to a service action they were never notified about. The locking and stalling reports both carry a real loss-of-control risk in traffic.

Sunroof glass blows outward while driving at about 45 mph, spraying sharp shards over everyone inside and leaving minor cuts. In that report no rock or debris was seen hitting the car, and the outside temperature was well below freezing. The other complaint is a rear-view mirror breaking loose at speed and striking the passenger window at about 23,000 miles. Neither failure gave any warning sign beforehand.