These instructions apply to the Smart Fortwo Mk2 (W451) 2007-2015. For other models, please choose your vehicle here.
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The Smart Fortwo (W451, 2007–2015) in mhd (micro-hybrid drive) form uses a Start/Stop system that shuts the engine off at a standstill to save fuel. If you’d rather keep it running — in traffic, when manoeuvring, or before working under the bonnet — you can switch it off with the dash button.
Turning Start/Stop Off
- Press the Start/Stop (ECO/mhd) button on the dashboard.
- The Start/Stop warning light changes state to show the system is now switched off.
It Resets Every Time You Start
Start/Stop re-enables automatically each time you start the engine. There’s no permanent off setting — press the button again after each start if you want it disabled.
If the System Won’t Stop the Engine Anyway
Even with Start/Stop active, the engine won’t cut unless conditions are met:
- The 12 V battery is sufficiently charged — short trips leave it too low.
- The engine is warm enough.
- The car is fully stopped.
A Start/Stop that rarely works on these cars is very often a tired battery.
Frequently Asked Questions
How do I turn off Start/Stop on a Smart Fortwo W451?
Press the Start/Stop (mhd) button on the dash — the warning light confirms it’s off.
Does it stay off permanently?
No — it re-enables every time you start the engine.
Why doesn’t the engine stop at lights?
Usually the battery isn’t charged enough or the engine isn’t warm yet.
Do all W451s have Start/Stop?
No — only the mhd micro-hybrid versions. Non-mhd cars don’t have the button.
If a Start/Stop fault light stays on, look up the code on autodtcs.com.
Disclaimer: The information on this page is provided for general guidance only. Always follow your official service manual and safety precautions when working on your vehicle. We are not responsible for errors, omissions, or any damage resulting from the use of this information.
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