If you own a Smart 451 diesel 54cv and your car often goes into protection mode , not exceeding 3000 rpm , especially uphill , you are not alone. Many owners complain about the same problem, often accompanied by error codes P0299 and P2359 . Let's see together what these errors mean , what interventions have already been attempted , and above all what you can really do to solve the problem once and for all .
WHAT DO ERRORS P0299 AND P2359 MEAN?
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Error P0299 : low boost pressure signal, meaning the turbine does not deliver the expected pressure.
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Error P2359 : Boost pressure fault – may be too high or too low.
These codes both refer to the turbocharging system , but often the turbine itself is not the culprit.
WHAT HAS ALREADY BEEN DONE? (AND WHY IT MIGHT NOT BE ENOUGH)
In the case of a desperate user, the Smart has already undergone several interventions, including:
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Cleaning the EGR valve
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Throttle body cleaning
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Replacing the vacuum solenoid valves
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Cleaning the particulate filter (FAP)
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Replacing the exhaust pressure sensor
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Turbine bench test, found to be working
Yet the car continues to go into protection.
POSSIBLE HIDDEN CAUSES AND HOW TO FIX THEM
Let's look at the less obvious but often responsible causes of the problem:
1. Damaged or porous vacuum lines
Even if the vacuum tubes are new, check all lines (especially near the turbine control valve ) for possible leaks.
2. Faulty turbine actuator
If the actuator (electronic or pneumatic) does not work properly , the turbine will not modulate the pressure. Even if the turbine is OK, if the actuator does not work, the control unit will limit the power.
3. Dirty or faulty MAP sensor
The manifold absolute pressure (MAP) sensor measures intake air pressure. If it sends incorrect values, it generates false boost alarms.
4. Wiring problems or oxidized connectors
Check the electrical connectors of the sensors (EGR, MAP, turbo pressure) carefully. Oxide or water infiltration will cause incorrect readings.
5. Engine control unit with corrupted or obsolete map
In rare but documented cases, a software update can resolve chronic turbo management anomalies.
WHAT CAN YOU DO IN PRACTICE?
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Smoke check with vacuum machine : to check for leaks in pipes.
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Real-time diagnostic test : to monitor turbo pressure, actuator position, EGR and MAP values while driving.
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Turbo actuator check : Hand pump test or diagnostic. It should move continuously.
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Cleaning the MAP sensor : with contact spray or replacement.
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ECU update : to be done only at workshops with official instrumentation.
FREQUENTLY ASKED QUESTIONS (FAQ)
❓ My Smart 451 diesel has the same problem: what should I do first?
Start with a vacuum test and check the turbine actuator and MAP sensor.
❓ Can I use additives for the FAP or EGR?
It can help in the preventive phase, but it does not solve an active error.
❓ If the turbine is ok, why does the car still go into protection?
Because the error is often due to what controls the turbine, not the turbine itself.
❓ Can the car get damaged if I continue to drive it like this?
In the long run, yes: driving in protection mode increases fuel consumption and can clog the FAP.
CONCLUSIONS
If your Smart 451 54cv diesel is suffering from problems related to errors P0299 and P2359 , do not despair . It is a common problem but it can be solved with a precise approach and professional diagnostics. Trust a mechanic expert in diesel and turbo systems , or ask for support from workshops specialized in Smart.
