Smart Fortwo 451 Fuse Quick-Reference Card
Tools you'll need
- Plastic fuse pull tool (lives in the fuse-box lid on most 451s)
- Phone flashlight
- Spare mini blade fuses in matching ratings (5, 7.5, 10, 15, 20, 25, 30A)
What this is + why it matters
A fuse is the cheapest thing on the car to replace, and a blown one is the cheapest first-thing-to-check on a long list of "the car is broken" symptoms. On a 451 specifically, a 5A or 10A fuse can mimic problems that look much scarier:
- Dead radio / infotainment with the rest of the car fine
- 12V outlet / cigarette lighter not powering a phone charger
- AC compressor not engaging even when the fan blows
- One headlight low-beam dark while the other works
- Brake light out that the dash flagged but the bulb is fine
- Power window dead on one side
- "Battery dead" symptoms that are really one circuit fed through a blown 5A
This page is the 451-specific deepening of the cross-chassis Fuse Box Layout page. Use that one to find the box; use this one for what's inside.
What you'll need
The 451 has its main owner-accessible fuse panel in the driver's footwell area, with the printed legend on the inside of the cover. The plastic fuse puller lives clipped into the lid on most cars. If yours is missing, fingers or thin needle-nose pliers work.
451 interior fuse panel — typical layout
Positions vary by year, market (NA / EU / JDM), and trim (coupe / cabrio / electric drive). Always verify against the legend printed inside your fuse cover — what's below is community-typical for 2008-2015 NA-spec petrol cars. If your cover legend disagrees with this table, the cover legend wins.
| Position | Amp | What it feeds | Symptom when blown |
|---|---|---|---|
| F1 | 30A | Cooling fan motor | Engine runs hot in traffic, AC degrades |
| F2 | 10A | ABS / ESP module power | ABS + ESP lights on dash |
| F3 | 7.5A | ECU / engine management | Crank but no start, or no crank |
| F4 | 15A | Fuel pump | Crank but no start, no fuel pressure |
| F5 | 10A | Headlight low-beam (left) | Left low-beam dark |
| F6 | 10A | Headlight low-beam (right) | Right low-beam dark |
| F7 | 10A | Headlight high-beam | High-beam dark, low-beam fine |
| F8 | 10A | Brake light circuit | Brake lights out, dash warning |
| F9 | 15A | Radio / infotainment | Head unit dead, speakers silent |
| F10 | 20A | 12V accessory outlet / cigarette lighter | Phone charger / outlet dead |
| F11 | 7.5A | AC clutch / climate control | AC won't engage, fan still blows |
| F12 | 15A | Power windows | One or both windows dead |
| F13 | 10A | Central locking / interior lights | Doors won't lock from key, dome light out |
| F14 | 5A | Instrument cluster / dash backlight | Dash dim or dark with key on |
| F15 | 20A | Wiper motor | Wipers won't run |
| F16 | 25A | Heated seats (where fitted) | Seats won't warm |
451 CDI-specific (diesel only)
| Circuit | Amp (typical) | What it feeds | Symptom when blown |
|---|---|---|---|
| Glow plug relay feed | 30A or 40A (heavy gauge) | Glow plug pre-heat | Hard cold start, glow light flashing |
| EGR valve power | 7.5A | EGR actuator | EGR fault code, possible limp mode |
| Fuel filter heater | 10A | Fuel filter heater (cold-climate cars) | Cold-weather fuel waxing risk |
CDI heavy-current fuses are often inside the engine bay relay box, not the interior panel. Check both covers.
Engine bay / SAM-adjacent fuses
The 451's main electrical control is centralized in the SAM (Signal Acquisition Module). Some heavy-current fuses live in or alongside the SAM rather than in the interior panel. These are owner-territory for swap-and-test, but the SAM itself is shop territory — see SAM Module Overview before going further.
Step by step
How to pull and check a fuse on a 451:
- Key off, ignition out. No need to disconnect the battery for a fuse swap, but do kill the ignition.
- Open the fuse cover. Driver's footwell panel — pull by hand or with a small flat screwdriver to release the clip on the corner.
- Find the puller. It clips into the inside face of the lid on most 451s. Looks like a small tan or black plastic clothespin.
- Identify the fuse for the dead circuit. Match the symptom against the legend on the cover or the table above. If the legend is rubbed off, the workshop manual has the full chart.
- Pull the suspect fuse straight out. Grip the body, not the metal blades.
- Inspect the filament. Hold it to a phone flashlight. The thin metal strip across the top should be intact. Broken or melted strip = blown.
- Replace with the same amp rating. Color-code is a fast eyeball check (red = 10A, blue = 15A, yellow = 20A) but the printed number on the fuse body is the source of truth.
- Push the new fuse in firmly. It should seat fully flush.
- Test the circuit. Ignition on, try the dead function. Working again = done. Still dead = the fuse wasn't the cause.
Do not swap a higher-amp fuse in to "make it work." If a 10A circuit blows 10A fuses, putting a 20A in lets the wiring carry a load it wasn't built for. That's how harnesses melt and cars catch fire. The fuse is doing its job — the circuit downstream is the problem.
Common gotchas
A new fuse blows immediately. There's a downstream short, not a bad fuse. Stop replacing fuses. The next step is finding the short — often a chafed wire, a failed component drawing too much current, or water in a connector. A repeating blow on a power-window fuse is frequently the regulator itself shorting (see Window Regulator Failure on 451).
Fuse looks fine but the circuit is still dead. The fuse is a witness, not always the cause. The next suspects are the relay (if there is one for that circuit), the wiring, or the load itself.
SAM module fuse failures look like interior fuse failures. The 451's SAM controls a lot of low-current logic that on older cars would be a discrete fuse. If a circuit is dead and the obvious fuse is fine, the SAM is the next suspect — not another fuse. SAM-related symptoms can overlap with codes that look like simple fuse problems but aren't.
Heat damage on the fuse box itself. Discolored plastic around a slot, melted blade contacts, brown staining on the bus bar — these mean the box itself is failing. Don't keep using a heat-damaged panel. Replace it or have a shop look at it before something catches fire.
Cabrio and electric drive 451s have extra circuits. Roof motors, drive battery contactors (ED only), heated mirrors on some trims. The cover legend on those cars covers the additions. Don't assume a coupe diagram applies.
When to skip DIY
A fuse that keeps blowing no matter what you do means a short to ground in the harness. That's a wiring trace job, often expensive on the driveway. A shop with proper diagnostic gear is the right call.
A fuse box with smoke smell or visible heat damage is not a swap-and-go situation. Stop, disconnect the battery, and get it inspected.
The SAM module itself is shop territory. Replacing a fuse that feeds the SAM is owner-fine. Replacing the SAM, or chasing a fault inside it, requires Star Diagnosis or equivalent and a coding step. Don't go past simple fuse replacement without diagnosis.
If the legend inside your cover is rubbed off and the workshop manual chart doesn't match what's actually in the panel — somebody's been in there before you. Trace each fuse against its actual circuit before assuming any reference is correct.
Manual references
Top reference manuals for this chassis (from our catalog of 88 Smart manuals):
- 1998-2015 smart fortwo (450 451) - Technical & Service Reference — Technical & Service Reference, 977p, 92.7 MB
- 2007-2014 smart (450 451 452 454) - Workshop Repair Manual — Workshop Manual, 4602p, 290 MB
- 2008 smart fortwo (451) - US Introduction into Service Manual — Introduction into Service Manual, 122p, 41.2 MB
- 2008-2015 smart fortwo (451) - DIY Remote Start Installation Guide (US) — DIY Remote Start Install, 3p, 0.4 MB
- 2012 smart fortwo Electric Drive (451) - 3rd Gen Introduction into Service Manual — Introduction into Service Manual, 92p, 2.3 MB
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