Power Window Regulator Failure on Smart Fortwo 451 / Forfour 453
Window won't roll up, only goes one direction, or dropped into the door? It's the regulator — a known wear point on every Smart generation. Door panel off, regulator out, replacement in.
Typical Symptoms
- Window won't roll up; motor sound on down-button but no sound on up-button
- Window stuck partway up or down
- Window dropped into the door cavity
- Audible scraping, clicking, or grinding from inside the door
- Sometimes works after a hard slap to the door (that's a regulator on borrowed time)
- Cold-weather sensitivity (winter triggers it on a marginal regulator)
What it means
Window regulators on the Smart Fortwo are a known wear point across all generations. The specifics differ by model:
- 450: regulator held in by 4 rivets — top and middle accessible from the front of the door, lower 2 from the back. Drilled out for replacement. Cable-style regulator that’s prone to the cable breaking; community-known cable-only repair kit available.
- 451: opposing Torx-30 bolts at the bottom of the door, two Torx-40 bolts holding the glass to the regulator. More straightforward access than the 450.
- 453: regulator rails with a Torx bolt at the bottom of each rail. Glass comes out before the regulator.
The most common failure modes:
- Motor still works, regulator broken — window slides freely up and down by hand once the door panel is off, but won’t hold position when motorized.
- Cable failure (450 mostly) — regulator is otherwise fine, the cable inside has snapped. Cheaper fix.
- Motor failed — less common; usually one direction works and the other doesn’t (the Reddit case linked above).
- Cold-weather binding — on a marginal regulator, freezing temperatures push it over the edge. The Reddit case here is a -16°C event where the up-direction stopped working entirely.
Likely causes (cheapest first)
- Cable broken (450 only). If you can hear motor noise but the window doesn’t move, and you have a 450, this is the first suspect. Cable kit and DIY procedure on Evilution.
- Regulator plastic worn or shattered. The plastic carrier that connects the cable/rail to the glass can disintegrate — one owner described it sounding like breaking glass.
- Motor failed in one direction. Less common but happens. If the motor sounds different up vs. down, suspect this.
- Switch failed. Cheap and easy — check by swapping a known-good switch from the other side.
- Frozen / cold-weather binding. Treat the seals with silicone, warm the car, try again.
DIY check steps
- Listen for the motor. Press the up button. Press the down button. Motor sound on down but no sound on up suggests a directional switch or motor issue, not a regulator. No motor sound either way points at switch, fuse, or motor.
- Check the fuse. On the 451, fuse 3 is "Window lifter motor, left and right" — 20A yellow. Free, 30 seconds.
- Try the other window’s switch. If swapping switches changes which window works, the switch is the issue.
- Door panel off. This is unavoidable for the rest. Door panel removal is well-documented on Evilution for each generation; tools needed are Torx drivers (T15, T20, T25, T27) and patience.
- With the panel off, try to slide the glass by hand. If it slides freely, regulator and glass tracks are fine — you’re looking at the motor or the cable. If it binds, the regulator’s mechanism is the issue.
- Inspect the regulator visually. Cracked plastic carrier, snapped cable, or a regulator that’s come off its rail will all be obvious once you can see it.
- Order the right part. Generation-specific — a 451 regulator does not fit a 453 and vice versa. Left and right are different on most years.
When to call a shop
If you’re not comfortable removing the door panel, this is shop work. A Smart-experienced shop will charge $200-450 depending on parts. Generic shops will sometimes charge more because they have to look up the procedure — ask if they’ve done a Smart window before.
For the 450 specifically, the cable-only repair (linked above) is a good middle path: cheaper than a full regulator, and a competent DIYer can do it in an afternoon. For the 451 and 453, the regulator change is straightforward enough that most Smart-comfortable owners can DIY.
If the window’s stuck down and there’s rain in the forecast: tape a plastic bag over the opening and budget the repair for this week. If it’s stuck up — you have time.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Window regulator (450) | $60-150 | Search Google |
| Window regulator (451) | $70-180 | Search Google |
| Window regulator (453) | $80-200 | Search Google |
| Window motor (separate part) | $50-150 | Search Google |
| Cable repair kit (450 only — community-known fix) | $30-60 | Search Google |
Prices are rough community-reported ranges, not quotes. Aftermarket vs. genuine Mercedes parts swing the spread; call a Smart-experienced shop for an actual quote.
Manual references
- Workshop / service manual PDF — full procedure with torque specs, hosted on smartcarmanuals.com.
- Browse Smart manuals on smartcarmanuals.com — pick your chassis code section on the home page if a specific manual isn't listed above.
Community references
- Evilution: 450 window regulator change
- Evilution: 450 window regulator cable (cheaper repair option)
- Evilution: 451 fortwo window regulator
- Evilution: 453 window regulator
- Reddit r/MechanicAdvice: 451 window won't roll up (cold weather case)
Stuck on this one?
SmartDiag-AI runs through the cheap-first checks with you, weighted to community-known patterns for your exact model. The link below pre-fills the code and model.