Quick Info
Model
450, 452
Estimated Cost
€15 – €25
Difficulty
Intermediate
Time Required
1 Hour
Safety Notes
Fire Hazard: You are working with raw gasoline. Ensure you are in a well-ventilated area, away from any open flames, sparks, or people smoking. Keep a fire extinguisher nearby.
Eye Protection: Fuel can spray out under pressure when disconnecting lines. Always wear safety goggles to prevent fuel from entering your eyes.
Fuel Pressure: Even with the engine off, the lines remain pressurized. Use a rag to cover the connections when popping the clips to catch any spray.
Skin Care: Gasoline is an irritant. Wear nitrile gloves and wash your hands immediately if fuel comes into contact with your skin.
Environmental Protection: Do not let gasoline soak into the ground. Use a proper catch pan and dispose of the old filter and fuel at a recycling center.
Step-by-Step Guide
Introduction
In the world of Smart Roadster maintenance, the fuel filter is one of the most frequently overlooked components. Hidden away beneath the plastic under-trays and exposed to the elements, it is often forgotten until the car starts showing symptoms of hesitation, poor idling, or a struggling fuel pump. Standard maintenance intervals suggest changing your fuel filter every 40,000 to 60,000 km (25,000 – 37,000 miles) or every 4 years.
However, if you are running a tuned engine or frequently use fuel from older stations, a more frequent 2-year interval is a smart insurance policy for your engine's health.
Because the Smart 450 and 452 engines are highly sensitive to fuel pressure, a clogged filter doesn't just reduce performance—it forces the fuel pump to work significantly harder, leading to premature (and expensive) pump failure.
Over thousands of kilometers, the filter traps microscopic debris, rust from fuel stations, and contaminants that can bypass the tank's internal mesh. If you are aiming for a Stage 1 or Stage 2 remap, or if you simply want to ensure your engine runs at the correct air-fuel ratio, a fresh filter is mandatory. This guide will show you how to navigate the underbody of your Roadster, release the pressurized clips safely, and install a new high-flow filter to keep your fuel system pristine.
Lifting and Undertray Access
Park the car on a flat surface and lift the side of the car (usually the passenger side for LHD models) where the fuel lines run. The filter is located near the rear wheel on the side of the fuel tank. Use an E-Torx (E10/E12) socket to remove the bolts securing the plastic undertray. You don't need to remove the whole tray; loosening the side section is usually enough to gain access to the filter housing.
Relieving Pressure & Positioning
Place a catch pan directly under the filter. Even if the car has been sitting, there will be residual pressure. To minimize the mess, you can remove the fuel pump fuse and crank the engine for a few seconds until it stalls, though using a thick rag over the connectors is the most common DIY approach. Locate the filter, which is held in place by a plastic bracket and three quick-release fuel lines.
Disconnecting the Quick-Release Lines
The Smart uses "push-and-pull" connectors. Press the colored plastic tabs on the fuel line connectors and gently pull them away from the filter. Be prepared for about 100-200ml of fuel to drain out. Pro Tip: Take a photo or note which line (blue or black) goes to which port on the filter before removal to avoid confusion during reassembly.
Swapping the Filter
Loosen the screw or clip holding the filter in the bracket. Slide the old filter out. Before sliding the new one in, check the direction of flow arrow printed on the side of the new filter. The arrow must point toward the engine (away from the tank). If installed backward, you will severely restrict fuel flow and potentially damage the pump. Slide the new filter into the bracket and tighten the mounting screw.
Connection and Leak Test
Push the fuel lines onto the new filter until you hear a distinct "click." Give each line a gentle tug to ensure they are locked. Before reinstalling the undertray, turn the ignition to position 2 (without starting) to prime the fuel pump. This will pressurize the system. Check all connections for leaks. If the area is dry, reinstall the undertray and lower the car.
