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Smart Fortwo 451 Cabrio Pre-Purchase Inspection — Roof, Slider and Fabric Buyer's Checklist

Easy 45-60 min Smart Fortwo 451 Cabrio

Service interval: Run through this list before money changes hands; not after

What this is + why it matters

This is the cabrio-specific layer on top of the standard 451 Pre-Purchase Inspection. The mechanical items — three-bar warning history, P0410 secondary air, P0303 cylinder 3, P0805 clutch actuator, window regulators, battery and OBD scan — all live on the parent page and apply to a cabrio just the same. Read that first.

This page is about what's different on a cabrio: the roof. Almost the entire incremental risk of buying a 451 Cabrio over a coupe sits in the soft top assembly. The fabric, the rear plastic window, the plastic sliders that ride in the tracks, the cables, the motor, the drainage channels behind the roof bow — that's where money disappears on a used cabrio. Replacement tops with labour run roughly $1,000-2,000. Slider and cable jobs can run similar territory if the motor has been grinding through worn parts for a while. None of that is exotic, but it adds up fast and it's all stuff a seller can hide in a 10-minute lot visit.

So the cabrio-specific items go at the start of your test drive, not the end. Cycle the roof first, while you're still in the lot and the engine is cold. If it doesn't behave, the rest of the inspection doesn't matter — you've already found your reason to negotiate hard or walk. If you save the roof for last, you're emotionally bought in and the seller has time to talk you out of trusting your eyes.

What you'll need

  • Flashlight — for trunk drainage channels and trim under the seats
  • OBD-II scanner — same one you'd use for the coupe PPI, codes are codes
  • A spot in the lot where you can fully open and fully close the top with no overhead obstructions
  • 45-60 minutes on-site, plus the standard test drive afterwards
  • Willingness to ask the seller for service records — including any roof / top service history
  • Optional but valuable: a phone with video, so you can record the roof cycling and rewatch it for hesitations

Step by step

  1. Cycle the roof three times — fully open, then fully closed, three full cycles. This is the single most important thing on this page. One cycle on a cold mechanism can hide intermittent binding; three cycles surfaces it. Listen for motor strain, any pause mid-travel, asymmetric movement (one side leading the other), or grinding. The cabrio top motor and cables are the #1 expense item on a used 451 Cabrio. A confident, even cycle on all three runs is a strong signal. Anything else is a yellow flag at minimum.
  2. Inspect the fabric top. Walk around the closed top with a flashlight. Look for tears (especially at seams), frayed stitching, daylight visible at the front rail when you're inside the cabin (water leak path), and any patching or repair work. Tug gently at seam edges — fabric that's about to separate often telegraphs.
  3. Inspect the rear plastic window. Cracks, deep scratches, crazing (a fine network of haze) and yellowing all reduce visibility and lower resale. A clear, supple rear window is normal on a well-cared-for cabrio. A hazy or cracked one means a top replacement is on the horizon and that's not cheap.
  4. Inspect the roof sliders. With the top in mid-position, look at the white plastic guides that ride in the tracks at each side. Cracking, deformation, flat spots, or stress marks on the sliders are a known wear item — see 451 Cabrio Roof Sliders. Per Richard Bowden, the UK Smart cabrio specialist, sliders are a roughly 4-year wear part regardless of how they look.
  5. Check the drainage channels at the rear corners. Open the trunk and look behind the rear bow where the top folds. There are drain channels here that route water out from the closed-top position. Leaves, dirt, and debris clog them, and once they're clogged water backs up into the trunk floor and the cabin carpet.
  6. Pull the floor mats and check for damp carpet. Under the seats and especially in the trunk area. Cabrio water ingress is more common than coupe ingress and it's a leading indicator of either clogged drainage or a tear in the rear seal. A musty smell with the doors closed is the same signal.
  7. Roof switch test from both sources. Cycle the roof from the in-dash switch, and if the car has the key fob roof function, test that too. Both should work cleanly. A switch that works one way and not the other is a wiring or module issue, not a top issue, but it's still something you'll be paying to fix.
  8. Standard 451 mechanical checks. Run the full 451 Pre-Purchase Inspection section: three-bar transmission warning history, P0410 secondary air, P0303 cylinder 3 misfire, P0805 clutch actuator, window regulators, battery health, OBD scan. None of the cabrio findings replace the mechanical checklist — they sit on top of it.

Common gotchas

  • "The roof works fine on the lot" doesn't mean the roof works fine. A slow, staggered, or hesitating cycle is the early warning sign of motor and cable wear, and one quick cycle won't surface it. Always cycle three times. If the seller gets impatient with that, the seller already knows.
  • Replacement cabrio tops are $1,000-2,000 with labour. Factor this into your offer, not your hopes. A car with a tired top that you "might fix later" is a car with a four-figure repair sitting in your driveway.
  • Damp trunk carpet on a cabrio is information. It's either a clogged drainage channel (cheap to fix once you know) or a tear in the rear seal (more involved). The diagnosis matters because the price tag does. Don't accept "it's fine, that's just from the car wash" without checking the channels yourself.
  • "I haven't put the top down in a year" — walk away. The mechanism seizes if it isn't exercised. A seller who hasn't cycled the top in a year either doesn't know it's broken or knows perfectly well and is hoping you won't ask. Either way, the next move is yours and it's the door.
  • The roof has a service procedure. Cable tension and end-stop teach-in adjustments are documented in the workshop materials. Ask if it's ever been done. A seller who knows the answer is a seller who's looked after the car. A blank stare isn't necessarily a deal-breaker, but it's a data point.
  • A cabrio that lives outdoors uncovered is a cabrio that ages faster. UV breaks down fabric coatings and plastic sliders alike. Garage-kept cabrios in the same year and mileage are worth the premium.

When to skip DIY

The whole point of this page is that you do this inspection yourself before money changes hands — there's no DIY to skip on the buyer side, only on the seller's promises to skip.

That said, if you can bring a Smart-experienced inspector to a cabrio purchase, do. A roof that doesn't cycle correctly is the single biggest hidden cost on a used 451 Cabrio, and an inspector who's seen the failure pattern before will catch the early-warning signs (asymmetric travel, motor pitch change at end-of-stroke, slider wear visible from the trunk side) that a first-time buyer won't. In the US, Cosmic Cabrios is the canonical mobile cabrio specialist. In the UK, Richard Bowden is the reference. A pre-purchase consult with either — even by phone, if you can describe what you're seeing — is cheaper than a top replacement.

If the inspection turns up a top that already binds, stops mid-cycle, or won't cycle at all, that's not a "we'll fix it after we buy it" car unless the price reflects the repair. Get the diagnosis right before you spend on parts that may not be the cause — see the 451 Cabrio Roof Sliders page for the full diagnostic flow.

Manual references

Top reference manuals for this chassis (from our catalog of 88 Smart manuals):

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