P0410 Secondary Air Injection System on Smart Fortwo 451
P0410 on a 451 is usually the secondary air injection switchover valve (Mercedes part 142147 / Smart A0025401497). Cheap part, 5-minute swap. Replace the valve before going after the pump.
Typical Symptoms
- Check engine light with code P0410
- Often shows up early — within the first 1,500–4,000 miles on early-production 451s
- No driveability issue you can feel; emissions test will fail
- Sometimes a brief vacuum or rushing noise on cold start
What it means
The secondary air injection system pumps fresh air into the exhaust just downstream of the cylinder head during cold starts. The extra oxygen helps the catalytic converter light off faster, lowering cold-start emissions. P0410 fires when the ECU thinks the system isn’t flowing the air it should.
On the 451 (M132 1.0L petrol), this fault has a strongly preferred culprit: the secondary air switchover valve — a small electrically-actuated vacuum valve. A bad batch of these from the factory pushed early-production 451s into P0410 within the first 1,500-4,000 miles. The problem persists in later cars too because the valve is a known wear part. Mercedes part 142147 (or Smart A0025401497) drops in for around $40 and the swap takes 5 minutes — two vacuum hoses and one electrical connector.
Likely causes (cheapest first)
- Switchover valve failed. The dominant cause. $40 part, 5-minute DIY. Try this first.
- 50A fuse in the battery compartment blown. The pump runs through this fuse; if it’s blown, the pump never spins.
- Vacuum hose cracked or off. Inspect the vacuum lines from the valve to the intake manifold and to the air supply path. Cracks or a hose that popped off will trip the code.
- Air line from pump to cylinder head leaking. Run the pump (audible on cold start when working) and listen / feel for leaks along the path.
- Secondary air injection pump failed. Less common than the valve but it does happen. Pump is mounted on the passenger-side frame rail below the alternator — replacement requires removing the right rear wheel and wheel-well liner. Some bolts are awkward.
DIY check steps
- Read the code, clear it, drive. Confirm it comes back — one-time codes can be noise.
- Listen for the pump on a cold start. It runs for ~30-60 seconds after a cold start when ambient is cool enough to trigger it (usually below 40°F / 5°C). If you hear a clear motor noise at startup, the pump is working — problem is downstream (valve, hose, or pipe).
- Check the 50A fuse in the battery compartment. Free, 30 seconds.
- Replace the switchover valve. Genuine Mercedes 142147 is reportedly more reliable than the original Smart-branded part. Two vacuum hoses, one plug. Done. Multiple SmartCarOfAmerica threads report this clears the code with no repeat failure.
- If the valve doesn’t fix it, inspect the vacuum hoses end-to-end and the air supply pipe from pump to cylinder head. Replace anything cracked.
- Pump replacement is last. Right rear wheel off, wheel-well liner out. A good number of YouTube tutorials cover this for the 451 if you want to DIY it — but most owners send it to a shop.
When to call a shop
If the valve, fuse, and visible vacuum hoses all check out, and the pump isn’t running on cold start — that’s shop territory. Pump access is awkward and the diagnosis from there benefits from a Smart-experienced tech with MB Star.
Honest note: P0410 is the one code most owners just live with. The car drives fine. The catalytic converter light-off is a hair slower than spec on cold starts — not something you’ll feel. Many 451 owners pop in a $40 valve once, and if that doesn’t clear it, they accept the check engine light and drive on. The exception: states with OBD-II emissions inspections (CA, NY, etc.) where the light is a fail.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Secondary air switchover valve (Mercedes 142147 / Smart A0025401497) | $37-50 | Search Google |
| Secondary air injection pump | $120-300 | Search Google |
| 50A fuse (battery compartment) | $2-5 | 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
- SmartCarOfAmerica: P0410 Check Engine Error Code, Secondary Air Injection System Fault (resolved)
- SmartCarOfAmerica: P0410 Secondary Air Injection System Malfunction (resolved)
- SmartCarOfAmerica: P0410 Error Secondary Air Injection System (2015 model)
- SmartCarOfAmerica: 451 Smart P0410 code (multi-component troubleshooting thread)
- Evilution: Specific error codes (P0410 reference)
Stuck on this one?
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