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Smart Fortwo Pre-Purchase Inspection — 450, 451, 453 Buyer's Checklist

Easy 30-60 min on-site inspection Smart Fortwo 450Smart Fortwo 451Smart Fortwo 453Smart Forfour 453

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

What this is and why it matters

This is a buyer's checklist, not a service guide. The goal isn't to fix anything — it's to find the things you'd otherwise discover the week after the car becomes your problem. Smarts are reliable cars when looked after, but each generation has a few signature issues that show up in pre-purchase inspections and turn a "great deal" into a year of repairs.

Read the section for the generation you're looking at, plus the universal items at the bottom. None of this requires special tools beyond a flashlight, an OBD-II scanner, and a willingness to ask the seller for service records. If you can bring a Smart-experienced inspector, do — they'll catch things this list won't. If you can't, this gets you 80% of the way there.

One rule that applies to every Smart purchase: ask for a recent OBD scan printout. Even an empty result tells you something. A seller who refuses or claims "the light doesn't mean anything" is telling you to walk.

How to use this checklist

  1. Print it or pull it up on your phone before you go.
  2. Walk through every item in the relevant generation section. Don't skip — the issues that bite hardest are the ones you didn't think to check.
  3. Drive the car. Not around the block — at least 20 minutes including some highway speed.
  4. Keep notes. After you leave, write down what you found. If you go to a second car, you'll want to compare.
  5. Get an OBD scan. Even a $25 Bluetooth dongle and a free app will tell you what the ECU has stored.

Buying a Smart Fortwo 450 (1998-2007)

The 450 is the original. They're old now — most are 18+ years — and that age is the dominant variable. What you're really inspecting is condition, not just mileage.

Known failure modes:

  • Alternator soft-seize on cars that sat. A 450 that's been parked for months can develop a sticky alternator that prevents cranking. See 450 Alternator Soft-Seize. Test: if the seller says "I had to charge the battery to get it started", that's a yellow flag — find out if the alternator was the issue.
  • Window regulators. Common failure point. Both windows up and down, watch for slow operation, grinding, or a window that drops freely. The Window Regulator page covers the 450 mechanism too.
  • Water leaks at the bulkhead. Pull the floor mats and check for damp carpet under the front seats. Smart 450s and Roadsters are known for water ingress through bulkhead seals. See Water Leak 451 / Roadster — same family of issue.
  • Tridion frame rust. The Tridion safety cell is steel and will rust, especially in salt-belt regions. Get under the car with a flashlight. Surface rust is normal and OK. Scaly, flaking rust at structural points (rocker rails, suspension mounts) is a deal-breaker.
  • Battery condition. A weak battery on a 450 cascades into hard starts and odd electrical behaviour. Check date code on the battery — anything over 4 years should factor into your offer.
  • Glow plugs (CDI variant). If it's a 450 CDI, glow plugs degrade over time and slow starting in cold weather is the symptom. Plan to replace if condition is unknown.
  • General age items. Hoses, belts, bushings, seat foam, soft trim. None of these are catastrophic individually; together they add up.

Test drive: Cold start matters most on a 450. Get to the car cold and watch how it starts. Hesitation, stumbling, or rough idle on cold start is information. The 450 should idle smoothly within 30 seconds. Listen for clutch noise on the automated manual — these gearboxes are quirky but should be predictable.

Bring a Smart-experienced inspector if you can. Generic mechanics don't know the 450 well. Ask for a recent OBD scan printout.

Buying a Smart Fortwo 451 (2007-2015)

The 451 is the most common Smart on the used market in North America and the UK. Plenty of choice, and plenty of cars with stories. The signature issues are well documented.

Known failure modes:

  • Three-bar transmission warning history. The 451 automated manual will sometimes throw the three-bar warning on the dash. See Three-Bar 451 Transmission Warning. On a used car, ask if the seller has seen this. A car with a documented teach-in / adaptation history is fine. A car with a recent three-bar light and no service is a question mark.
  • Clutch actuator wear past 100k miles. The 451's clutch actuator is the wear part on this transmission. Past 100,000 mi, plan for it. See P0805 Clutch Actuator. Symptoms: slow shifts, harsh shifts, or warnings under load.
  • Secondary air injection valve. Throws P0410 codes. See P0410 Secondary Air. On the 451 M132, this is a known wear item. Check OBD for stored or pending codes.
  • Cylinder 3 misfire and valve health. The 451 M132 has a known issue with cylinder 3 in particular — see P0303 451 Misfire. Symptoms: rough idle, misfire codes, sluggish power. On test drive, listen for any miss under load.
  • Cabrio top condition (cabrio buyers only). Roof slider condition and fabric care matter. See 451 Cabrio Roof Sliders and Convertible Top Maintenance. Cycle the top fully open and fully closed at least twice. Listen for binding or any pause mid-cycle. Look at the fabric and the rear plastic window — replacement tops are not cheap.
  • 451 CDI: timing belt history is critical. The CDI runs a timing belt and replacement at the right interval is non-negotiable. If service records don't show the timing belt done at the documented interval, factor a belt service into your offer (or walk). See Timing Belt CDI.
  • Battery and charging system. As with the 450, age-related electrical weirdness is worth checking. Stable cold-start, normal alternator output.

Test drive: Take it on the highway. Get up to 60-65 mph and listen for vibration, noise from the rear (engine bay), or any clutch shudder. The 451's automated manual has a characteristic shift pause that's normal — what you're listening for is harshness, slipping, or warning lights.

Bring a Smart-experienced inspector if you can. Ask for a recent OBD scan printout.

Buying a Smart Fortwo 453 / Smart Forfour 453 (2015-2024)

The 453 is the most modern Smart and the platform with the longest expected service life ahead of it. The issues are different — more electronic, less mechanical — and the parts costs trend higher because the platform is newer and more integrated.

Known failure modes:

  • Valve cover gasket leaks into cylinder 3 plug well. Common on the 453 H4Bt turbo. Oil pools in the spark plug well, fouls the coil and plug, and throws P0303. See P0303 453 Valve Cover Oil-Fouled. Pull the coil cover and look at the plug wells — oil sitting in the well is a yellow flag.
  • DCT software update history. The 453 twinamic DCT had several software revisions during the production run. Harsh shifts, poor low-speed creep, or hesitation can be software-fixable. See P0128 453 DCT Harsh Shifts. Ask if the car has had the latest control unit software.
  • Passenger occupant sensor / SRS warning history. The 453 has known issues with the passenger seat occupancy sensor that throw SRS / airbag warnings. See B00A068 Passenger Occupant Sensor. On the test drive, watch the airbag light. If it's on, find out why before buying.
  • Auxiliary battery condition. The 453 has a small auxiliary 12V battery that supports the start-stop and electronics. Failure causes a parade of weird electrical warnings — battery, ESP, ABS — long before the car won't start. Plan to replace if older than 4-5 years.
  • F2K5 / SAM module starter relay history. The 453 SAM (signal acquisition module) has a known starter relay issue tracked under B152014. See B152014 F2K5 Starter Relay. Symptoms: intermittent no-start that goes away on retry. Ask the seller if the car has ever failed to start unexpectedly.
  • Tire wear pattern. The 453 is heavier than the 451 and tire wear shows up faster. Even shoulder-to-shoulder wear is normal; one-sided wear suggests alignment.
  • Software-related warnings on the dash. The 453 has more electronics than any prior Smart and a stored fault is more likely than on a 451. A clean OBD scan is reassurance; a long list of stored codes deserves investigation before purchase.

Test drive: The 453 should feel modern. Stop-start cycling should be smooth. The DCT should creep cleanly from a stop. Hard shifts, prolonged hesitation when launching, or low-speed shudder are flags. On the highway, the auxiliary systems (ESP, ABS, hill-start) should not throw warnings.

Bring a Smart-experienced inspector if you can. Ask for a recent OBD scan printout.

Universal items (every generation)

Whatever generation you're looking at, these apply:

  • Service records. A folder of receipts is worth a lot. No records is a discount, not a deal-breaker — but factor in the cost of catching up on every interval.
  • VIN match and title. The VIN on the car (door jamb, dashboard, engine bay) should match the title. Verify before you hand over money.
  • OBD scan printout. Cleared codes can re-appear in 50-100 miles. A car that's just been "scanned clean" by the seller might have had codes cleared moments before.
  • Tire condition and date codes. All four tires should be the same brand and similar wear. Mismatched tires on a Smart often indicate a budget-conscious previous owner.
  • Underbody inspection. Lift the car if you can, or get under it with a flashlight. Look for fluid leaks, rust, hanging exhaust, and damaged splash shields.
  • HVAC operation. AC blows cold? Heater blows hot? Defroster works? These are easy on a test drive and expensive when broken.
  • All electronics. Every window, every light, every switch. The radio, the dome light, the dash gauges. Five minutes of "press every button" finds problems that aren't obvious otherwise.
  • Recent battery. Battery date codes are stamped on the case. Anything older than 4 years is on borrowed time.

What this doesn't cover

  • A mechanical compression test or leak-down test. Worth doing on any high-mile car, but it requires tools and access most buyers won't bring.
  • Detailed body and paint inspection — accident history, panel alignment, repaint detection. A body shop can tell you in 15 minutes for a small fee.
  • Title-specific issues (lien holders, branded titles, salvage history). A vehicle history report (Carfax, Autocheck) is cheap insurance.
  • Generation-specific accessory issues (panoramic roof seal on certain trims, factory navigation deactivation, etc.).

If a seller is unwilling to let you take the car to an inspector, or refuses to share service records, walk away. The Smart-buying market has enough cars that you don't need to settle for one with red flags.

Manual references

Related fault codes

Related maintenance