IsItAGoodCar
Reliability Guide

Common Problems with the
2009–2014 Smart Fortwo (451)

We've identified 3 known issues that can affect the 2009–2014 Smart Fortwo (451). 2 of these are serious faults that could be expensive to repair.

3
Known Issues
2
Serious
1
Moderate
0
Minor

All Known Issues

MHD Drive Belt Failure

SeriousEngine

The Mild Hybrid Drive system uses a belt to start the engine and drive the water pump. If the belt snaps, the engine will overheat almost instantly, often warping the head.

Est. Repair Cost: £200 (belt) to £2,500 (engine rebuild)
Warning Signs:

Battery light on dash, Engine temperature warning, Sudden loss of power

What to Inspect:
  • Ensure the "Modified" belt kit and tensioner have been installed (Service Campaign work)
Verified by IsItAGoodCar Research Team

SAM Unit Corrosion (Water Ingress)

SeriousElectrics & Electronics

In the UK, water can enter the cabin via the door seals or heater intake and track down to the SAM unit (located in the passenger footwell).

Est. Repair Cost: £500–£1,000
Warning Signs:

Lights coming on by themselves, Dead battery, Non-start issues

What to Inspect:
  • Check for moisture under the passenger side carpet
Verified by IsItAGoodCar Research Team

Clutch Actuator Failure

ModerateGearbox & Transmission

The actuator that operates the clutch can seize or wear out, leading to jerky gear changes or failure to select drive.

Est. Repair Cost: £300–£600
Warning Signs:

Jerky pull-away, Slow gear changes, Car stuck in neutral with "3 bars"

What to Inspect:
  • Listen for a "creaking" noise from under the car when the ignition is turned on
Verified by IsItAGoodCar Research Team

Buying Tips for 2009–2014 Smart Fortwo (451)

  • Check the automated manual gearbox for hesitation; while improved, the clutch actuator still requires periodic electronic adjustment and lubrication.
  • Listen for a rattling noise on startup from the 1.0-litre Mitsubishi engine, which can indicate timing chain wear on high-mileage examples.
  • Inspect the panoramic roof (if fitted) for crazing or cracking in the polycarbonate material.
  • Check the operation of the air conditioning; condenser failures are common due to stone damage at the front of the car.
  • Look for dampness in the boot area, as the rear window seals can leak over time.
  • Ensure the heater blower motor operates smoothly; they are prone to squeaking and failing, and replacement is awkward.
2008
Check a 2009–2014 Smart Fortwo (451) by Registration