None of the petrol engined smart fortwo 451 have a replaceable fuel filter.
999cc petrol non turbo - no replaceable fuel filter
999cc petrol non turbo MHD - no replaceable fuel filter
999cc petrol turbo - no replaceable fuel filter
The fuel filter is part of the fuel pump and it is designed to last the life of the car.
I'm not sure what they class as the car's lifetime but it should outlive the fuel pump itself.
Changing the pump is a very difficult task as there is no service hatch above the pump.
This means the only way to change the pump is to lower and remove the fuel tank.
The 451 diesel does have a changeable fuel filter. As with the 450, it is hidden behind the offside
rear wheel arch liner. If you remove the arch liner, you'll see the metal filter in front of the wheel.
There seems to be 2 types of filter for the diesel 451.
The 45bhp diesel engine had a standard metal fuel filter.
The 54bhp diesel engine had a very similar filter but it had an earth lead connection.
Why the 2 models had a different earthed and non earthed filter set-up, I don't know.