2015 BMW 420i: common problems and MOT failures

What goes wrong more than usual on a 2015 BMW 420i?

Parts flagged at MOT more often on the 2015 BMW 420i than on all cars registered in 2015.

• Steering rack inner joints2.9× usual
  BMW 420i

  2.3% All 2015 cars

  0.8%

  Failed outright at MOT: 0%, against 0% of all 2015 cars. The rest were advisories or minor defects.

  Rough price £100–£450 our estimate

  At the viewing: On a straight road the steering wheel should sit straight. Listen for knocks when turning, and check the steering feels even.

Common 2015 BMW 420i MOT failures and advisories

The share of 2015 BMW 420i MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.

• Tyres
  28% of testsRough price £70–£150

  At the viewing: Check the tread on all four tyres, including the inside edges, and look for cracks or bulges.

• Brakes
  19% of testsRough price £150–£350

  At the viewing: Look for a lip on the disc edges and feel for judder or pulling when braking firmly from about 40mph.

• Suspension
  7% of testsRough price £120–£400

  At the viewing: Listen for knocks over speed bumps, and look behind each front wheel for a snapped coil spring.

• Lights and electrics
  6% of testsRough price £10–£80

  At the viewing: Ask a friend to check every light, including brake lights and indicators, while you operate them.

• Wipers, windscreen and mirrors
  4% of testsRough price £15–£250

  At the viewing: Check for chips in the driver's view, and test the wipers and washers.

• Steering
  3% of testsRough price £100–£450

  At the viewing: On a straight road the steering wheel should sit straight. Feel for play or knocking when turning.

Known faults on the 2015 BMW 420i

Reported by owners, mechanics and buying guides for this model and age. Check which engine the car has, as some apply to one engine only.

• Timing chain wear

  2.0 petrol and diesel

  The four-cylinder petrol and diesel engines (shared with the 3 Series) can suffer timing chain wear, especially with late oil changes. A failed chain is an engine-out repair.

  At the viewing: Listen for a rattle or whine from the back of the engine, especially from cold. Ask for oil changes on time.

  Source: Parkers: BMW 3 Series (2012-2019) used review (the 4 Series shares its engines and running gear)

• Blocked EGR valve or particulate filter (diesel)

  Diesel

  Diesels used mostly for short trips can block the EGR valve or clog the particulate filter, causing poor running.

  At the viewing: Ask what journeys it’s done and watch for warning lights or a lack of power.

  If it needs doing: DPF clean or regeneration, about £160–£500. ClickMechanic

  Source: Parkers: BMW 3 Series (2012-2019) used review (the 4 Series shares its engines and running gear)

• Noisy differential

  A whine from the rear as the car passes you can mean the differential has been neglected.

  At the viewing: Ask someone to drive it past you slowly and listen for a whine from the back.

  Source: Parkers: BMW 3 Series (2012-2019) used review (the 4 Series shares its engines and running gear)

Questions to ask the seller before buying a 2015 BMW 420i

Ask before you travel to see it. A seller who knows the car will have answers, and receipts.

1. Has the timing chain been checked or replaced, and have oil changes been on time?
2. Any recent work on the steering rack inner joints? (Flagged at MOT 2.9× as often on the 2015 BMW 420i as on other cars the same age.)
3. Can I see the service history and receipts for any big jobs?