2009 Mercedes-Benz B-Class diesel: common problems and MOT failures

What goes wrong more than usual on a 2009 Mercedes-Benz B-Class diesel?

Parts flagged at MOT more often on the 2009 Mercedes-Benz B-Class diesel than on all cars registered in 2009.

• Rigid brake pipes4.1× usual
  Mercedes-Benz B-Class

  29.3% All 2009 cars

  7.2%

  Failed outright at MOT: 5.3%, against 1.2% of all 2009 cars. The rest were advisories or minor defects.

  Rough price £100–£400 our estimate

  At the viewing: Ask to see underneath, or check the MOT advisories: corroded brake or fuel pipes get worse every year and fail the MOT when they do.

• Drive shaft (CV) joints2.4× usual
  Mercedes-Benz B-Class

  11.6% All 2009 cars

  4.9%

  Failed outright at MOT: 5.6%, against 2.3% of all 2009 cars. The rest were advisories or minor defects.

  Rough price £60–£350 our estimate

  At the viewing: Drive slowly on full steering lock in both directions and listen for clicking. Look for split rubber boots behind the front wheels.

• Ball joint1.8× usual
  Mercedes-Benz B-Class

  11.1% All 2009 cars

  6.3%

  Failed outright at MOT: 6.3%, against 3.4% of all 2009 cars. The rest were advisories or minor defects.

  Rough price £60–£150 (one joint) ClickMechanic

  At the viewing: Listen for knocking over bumps and check the rubber boots behind the wheels aren't split.

• Steering rack inner joints2.8× usual
  Mercedes-Benz B-Class

  6.5% All 2009 cars

  2.3%

  Failed outright at MOT: 0%, against 0% of all 2009 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.

• Corroded fuel pipes8.6× usual
  Mercedes-Benz B-Class

  4.3% All 2009 cars

  0.5%

  Failed outright at MOT: 0%, against 0% of all 2009 cars. The rest were advisories or minor defects.

  Rough price £100–£400 our estimate

  At the viewing: Ask to see underneath, or check the MOT advisories: corroded brake or fuel pipes get worse every year and fail the MOT when they do.

Common 2009 Mercedes-Benz B-Class diesel MOT failures and advisories

The share of 2009 Mercedes-Benz B-Class diesel MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.

• Brakes
  51% 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
  38% 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.

• Tyres
  34% 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.

• Lights and electrics
  28% of testsRough price £10–£80

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

• Driveshafts and joints
  12% of testsRough price £60–£350

  At the viewing: On full steering lock, drive slowly and listen for clicking from the front wheels.

• Wipers, windscreen and mirrors
  10% of testsRough price £15–£250

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

Questions to ask the seller before buying a 2009 Mercedes-Benz B-Class diesel

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

1. Any recent work on the rigid brake pipes? (Flagged at MOT 4.1× as often on the 2009 Mercedes-Benz B-Class diesel as on other cars the same age.)
2. Any recent work on the drive shaft (cv) joints? (Flagged at MOT 2.4× as often on the 2009 Mercedes-Benz B-Class diesel as on other cars the same age.)
3. Any recent work on the ball joint? (Flagged at MOT 1.8× as often on the 2009 Mercedes-Benz B-Class diesel as on other cars the same age.)
4. Can I see the service history and receipts for any big jobs?