2014 vs 2015 BMW 4 Series

Both years

• Water trapped in the convertible's rear side panels All years

  What to check: Listen for water sloshing in the rear side panels while driving, run each rear window and the roof, and look for water or a musty smell in the corners of the trunk. Ask whether the drains have been cleared.

  BMW of North America's bulletin says the rocker trim and underbody panel can sit too tight against the drain plugs, so water fills the lower rear side panels and can corrode the rear window regulators and motors, then reach the trunk's audio amplifier. It extends coverage of the drain repair to 15 years or 150,000 miles from first delivery. On a British owners' forum, owners of four convertibles in three threads report a rear window or the roof stopping working from water in the panel, and another found water running out of a sill after a car wash.

  BMW, owners' reports (unofficial)

• Timing chain stretch on the N20 four 2014–2016 One source so far

  What to check: Listen for a rattle at idle, and ask whether the timing chain and its guides have been replaced.

  Euro Premium Parts calls the timing chain a major weak point, with plastic guides that can break and wreck the engine.

  A seller's guide (unofficial)

• Oil use and leaks on the N20 four 2014–2016 One source so far

  What to check: Look for blue smoke when accelerating and oil around the valve cover, and ask how often the oil has needed topping up.

  Euro Premium Parts says oil use can start as early as 60,000 miles, from a faulty crankcase vent valve, worn valve stem seals or, at worst, worn rings, and lists coolant leaks at the back of the block and cracked boost hoses.

  A seller's guide (unofficial)

• Oil leaks on the N55 six 2014–2016 One source so far

  What to check: Look for oil around the valve cover, the oil filter housing and the oil pan.

  Euro Premium Parts lists leaks from these gaskets, and carbon on the intake valves.

  A seller's guide (unofficial)

Both years

• 15V189000 2014–2015

  Poor nickel plating inside the fuel pump can make it fail. Dealers replace the fuel pump. NHTSA

• 24V288000 2014–2015

  The head airbag's inflator can fail at a weld, leaking gas or rupturing. Dealers replace the head airbags. NHTSA

• 24V527000 2014–2015

  The driver's airbag inflator may explode when it deploys, because of a manufacturing defect. Dealers replace the driver's airbag. NHTSA

• 24V608000 2014–2016

  A badly sealed electrical connector on the water pump can let water in and short circuit. Dealers inspect and replace the pump and connector as needed and fit a shield. NHTSA

Both years

Engines

2.0L turbo four-cylinder (2014–2016) Edmunds, a published reference, 3.0L turbo inline-six (2014–2016) Edmunds, a published reference

Transmissions

Eight-speed automatic Edmunds, CarGurus, Six-speed manual Edmunds, CarGurus

Drivetrains

Rear-wheel drive Edmunds, a published reference, xDrive all-wheel drive Edmunds, CarGurus

Body styles

Coupe Edmunds, a published reference, Convertible Edmunds, CarGurus, a published reference

Packages

Sport Line (2014–2015) Edmunds, Luxury Line, later Luxury Package Edmunds, a published reference, M Sport Edmunds, a published reference, Premium Package Edmunds, Technology Package Edmunds, Lighting Package Edmunds, Cold Weather Package Edmunds, Driver Assistance Package Edmunds, Driver Assistance Plus Package Edmunds, Dynamic Handling Package (2014–2015) Edmunds

Both years

• Watch for: A 428i without timing chain or engine records 2014–2016 Less sought after One source so far

  Euro Premium Parts says the N20 four-cylinder cars are best avoided unless the engine has been rebuilt or carefully maintained. A seller's guide (unofficial)