2012 Mercedes-Benz C-Class diesel: common problems and MOT failures

What goes wrong more than usual on a 2012 Mercedes-Benz C-Class diesel?

Parts flagged at MOT more often on the 2012 Mercedes-Benz C-Class diesel than on all cars registered in 2012.

• Rigid brake pipes4.9× usual
  Mercedes-Benz C-Class

  24.3% All 2012 cars

  5%

  Failed outright at MOT: 4.7%, against 0.8% of all 2012 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.

• Ball joint2.6× usual
  Mercedes-Benz C-Class

  13.5% All 2012 cars

  5.2%

  Failed outright at MOT: 8.2%, against 2.9% of all 2012 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.

• Link ball joint covers3.7× usual
  Mercedes-Benz C-Class

  7.4% All 2012 cars

  2%

  Failed outright at MOT: 3%, against 1.1% of all 2012 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.

• Wheel bearings4.2× usual
  Mercedes-Benz C-Class

  5.9% All 2012 cars

  1.4%

  Failed outright at MOT: 0.4%, against 0.5% of all 2012 cars. The rest were advisories or minor defects.

  Rough price £120–£300 (one bearing) ClickMechanic

  At the viewing: Listen for a hum or growl that changes as you steer at speed.

• Ball joint dust cover2.4× usual
  Mercedes-Benz C-Class

  5.8% All 2012 cars

  2.4%

  Failed outright at MOT: 2.4%, against 1.1% of all 2012 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.

Common 2012 Mercedes-Benz C-Class diesel MOT failures and advisories

The share of 2012 Mercedes-Benz C-Class diesel MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.

• Brakes
  43% 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
  34% 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
  33% 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
  17% of testsRough price £10–£80

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

• Oil and fluid leaks
  7% of testsRough price £80–£600

  At the viewing: Look under the engine and on the ground where the car is usually parked for fresh oil or fluid.

• Wipers, windscreen and mirrors
  6% of testsRough price £15–£250

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

Known faults on the 2012 Mercedes-Benz C-Class diesel

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.

• Injector seals (diesel)

  Diesel

  Injector seals and other engine seals can leak on the diesels.

  At the viewing: Look for fuel or oil around the top of the engine.

  Source: Parkers: used Mercedes C-Class 2007-2014 review

• Dual-mass flywheel (manual diesel)

  Manual diesel

  Manual diesels can wear out their dual-mass flywheel. Above 60,000 miles, check whether it's been done.

  At the viewing: Listen for a rattle at idle and judder pulling away.

  If it needs doing: Clutch and dual-mass flywheel, about £650–£1,200. ClickMechanic

  Source: Parkers: used Mercedes C-Class 2007-2014 review

• Harsh 7G-Tronic automatic

  Automatic

  Later automatics can change gear harshly, and repairs are expensive.

  At the viewing: Check changes are smooth from cold and at low speed.

  If it needs doing: Gearbox sensor or solenoid, about £200–£500. ClickMechanic

  Source: Parkers: used Mercedes C-Class 2007-2014 review

Questions to ask the seller before buying a 2012 Mercedes-Benz C-Class diesel

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

1. Have the injectors or seals been replaced?
2. Have the clutch and flywheel been replaced?
3. Has the gearbox been serviced?
4. Any recent work on the rigid brake pipes? (Flagged at MOT 4.9× as often on the 2012 Mercedes-Benz C-Class diesel as on other cars the same age.)
5. Any recent work on the ball joint? (Flagged at MOT 2.6× as often on the 2012 Mercedes-Benz C-Class diesel as on other cars the same age.)
6. Any recent work on the link ball joint covers? (Flagged at MOT 3.7× as often on the 2012 Mercedes-Benz C-Class diesel as on other cars the same age.)