P0302 Cylinder 2 Misfire on Smart Fortwo 451 / 453
P0302 is a misfire on cylinder 2. On the 451 it shares the same coil/plug swap logic as P0301 and P0303, but there's also a documented valve seat issue on the naturally aspirated 451 that can drop compression on cylinder 2. On the 453 turbo, oil in the plug well from a leaking valve cover gasket can cause P0302. Always run the swap tests first before suspecting a valve problem.
Typical Symptoms
- Check engine light with P0302
- Rough idle, especially when cold
- Hesitation under acceleration
- Slight loss of power
- Sometimes a low-compression result on cylinder 2 in high‑mileage 451s
What it means
P0302 means cylinder 2 is misfiring. In the three‑cylinder Smart engines it's the middle cylinder – moderate heat exposure. The first-line diagnostics are the same as P0301 and P0303: swap the coil and plug. The wrinkle is a real, documented valve-not‑seating issue on the 451 naturally aspirated engine that some dealers have repaired under goodwill. On the 453 turbo, oil leaking into the plug well from a valve cover gasket will misfire this cylinder.
Likely causes, cheapest first
- Ignition coil failed. Common and heat-related.
- Spark plug worn or fouled. Replace all three if they're over 30,000 miles.
- Fuel injector connector loose or wiring damaged. Less common.
- Valve cover gasket leaking into the plug well (453 turbo). Oil around the plug is a tell.
- Burned exhaust valve or valve not seating properly (451 NA). Confirmed by a compression or leak‑down test.
DIY check steps
- Perform a coil swap test: move the cylinder 2 coil to another cylinder and vice versa. Clear the codes and drive normally; see if the misfire follows the coil.
- Swap the spark plug in the same way. Replace the set if they're due.
- On a 453, check the plug well for oil while the coil and plug are out. Oil means the valve cover gasket needs replacement.
- If both swap tests pass, perform a compression or leak‑down test on cylinder 2. A compression gauge is inexpensive; leak‑down kits are also available.
When to call a shop
A compression or leak‑down failure on cylinder 2 points at a valve job on the 451; dealers have handled some of these as goodwill, so call with your VIN. On the 453 with oil in the plug well, the fix is a valve cover gasket. DIY is possible but tight; shops charge 3–5 hours plus parts. For high-mileage cars with low compression across multiple cylinders, a used engine may be a more economical option.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Ignition coil pack (single) | $25-150 | Search Google |
| NGK / Bosch spark plug | $8-18 each | Search Google |
| Fuel injector | $80-180 | 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
- Service manual on Manualslib — external mirror (we don't host this specific document).
- 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
- NHTSA complaint 10714370 (2011 Fortwo, cylinder 2 leaking 75%, dealer goodwill cylinder head repair, 14 of these to date)
- NHTSA complaint 11075948 (P0302 known issue, valve not seating properly)
- Evilution: OBD-II error code reference
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.