P2359 EGR Vacuum System on Smart Fortwo 451 CDI
P2359 on a 451 CDI puts the engine in safe mode (won't rev over 3000rpm). It's almost always a vacuum hose leak or check valve failure — not a bad EGR valve.
Typical Symptoms
- Check engine light with code P2359 (sometimes also P0234 or P1041–P1048)
- Engine won't rev above 3000 RPM
- Loss of power, especially climbing hills or merging
- 54bhp diesel 451 (the post-October 2009 EU5 diesel)
- 45bhp pre-2009 diesel rarely sees this
What it means
P2359 is an EGR-related fault on the 54bhp 451 CDI diesel — the post-October 2009 Euro-5 diesel. The pre-2009 45bhp diesel is essentially the same Mercedes-built three-cylinder engine going back to 2000, but Smart added DPF and additional emissions kit for Euro-5 compliance, and that’s where the trouble started.
When P2359 trips, the engine drops into safe mode and won’t rev above 3000 RPM. The code itself points at "incorrect pressure readings for the EGR" — but as Evilution notes in the canonical write-up, the EGR valve itself is rarely the actual culprit. It’s a simple solenoid; they don’t fail often.
What does fail: the vacuum hoses, vacuum accumulator, and check valves that feed the EGR’s vacuum-operated piston. A small leak anywhere in that vacuum network will trip P2359 (or related P1041-P1048 codes).
You may also see P0234 (boost too high) alongside P2359 — same root causes from the same vacuum network feeding the wastegate.
Likely causes (cheapest first)
- Cracked or split vacuum hose. The most common cause. Inspect all the small vacuum lines around the EGR valve, throttle body, and wastegate.
- Vacuum hose popped off a fitting. Easy to miss; trace each line to its end.
- Failed vacuum check valve. Cheap part, easy swap.
- Vacuum accumulator (globe) leaking. Less common but does happen with age.
- MAP sensor faulty. Per Evilution’s specific codes reference, P2359 on a 451 CDI can also indicate a faulty MAP sensor (or boost leak / wastegate issues).
- EGR control vacuum valve failed. Last on the list. Replace only after the vacuum network and MAP sensor check out.
- DPF blocked. If the car’s old, sat a lot, or done lots of short trips — the DPF may be the underlying issue. Evilution: "the DPF is blocked. Nothing will help. You’ll have to remove the exhaust and either replace it or find a company that will." Worst case.
DIY check steps
The EGR control vacuum valve sits just behind the throttle body when standing at the back of the car. Two-pin electrical connector, two vacuum/pressure pipes coming from it. Removing the throttle body and rubber pipe makes access to the valve much easier.
- Read the codes. P2359 alone vs. P2359 + P0234 + P1041-1048 all point at the same vacuum network — but multiple codes confirm vacuum is the area.
- Smoke test the vacuum system. A smoke generator pumps low-pressure smoke into the vacuum network and visibly shows where it leaks. Cheap leak testers exist for $30-60. This is the fastest way to find a hose leak.
- Visual inspection. With the throttle body out, look at every vacuum line for cracks, kinks, hardening, or hoses that have popped off.
- Check the vacuum accumulator (red globe in Evilution’s color-coded reference). Listen for hissing with the engine running.
- Check the EGR check valve. Yellow per Evilution’s color code. Should hold vacuum in one direction, release in the other.
- MAP sensor test. Check the MAP sensor reading vs. expected boost values. If it’s reading wildly off at idle vs. cranking, replace it.
- Only replace the EGR control vacuum valve if all the above check out. It’s a simple solenoid — rarely the actual fault.
When to call a shop
If smoke testing comes up clean and the MAP sensor and EGR valve both check out, the next suspect is the DPF. DPF diagnostics and forced regeneration need diagnostic equipment (MB Star or Xentry) and the resolution can be expensive — replacement DPFs are not cheap. A Smart-experienced diesel shop is the right call.
The 451 CDI in general is a tough engine but the post-2009 Euro-5 emissions kit is the Achilles' heel. If you’re shopping for a CDI, the 45bhp pre-October 2009 cars are widely considered the more reliable choice on the diesel side. Evilution covers the full safe-mode-causes catalog at the link above — worth reading end-to-end.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| EGR control vacuum valve | $30-90 | Search Google |
| Vacuum hose set | $10-30 | Search Google |
| Vacuum check valve | $8-20 | 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: P2359 451 CDI fault (the canonical write-up)
- Evilution: 451 diesel 54bhp safe mode (full context)
- Evilution: Specific error codes (P2359 entry)
Stuck on this one?
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