TorqFix
OM660 Mercedes-Benz (Smart) Diesel 2007-2014

OM660 engine — Smart 0.8 diesel (0.8L I3)

0.8L I3 · 41-45 hp · 110 Nm

The OM660 is the 799 cc three-cylinder common-rail diesel used by Smart, rated at 41 to 45 hp with 110 Nm. This page covers the W451 ForTwo CDI built from 2007 to 2014. For its size it is robust, and most faults come from how these cars are used: short city trips load the DPF and clog the small EGR passage, while the small turbo suffers from oil-feed restriction and hot shutdowns. Injectors can stick, the timing chain, balance-shaft chain and tensioners wear at higher mileage, and the Softip automated clutch actuator is a regular visitor. Torque figures cover main bearing caps, con rods, cylinder head, injector clamp, oil drain plug and wheel bolts.

Begin with a return-flow test on all three injectors for hard starting, smoke or rough idle, and code any replacement. Then check DPF soot loading and the EGR valve, which share the same cause on city cars. Turbo noise calls for an oil-feed check, and jerky engagement is usually the clutch actuator, which needs recalibrating after repair. Keep an eye on oil level, as the sump is small.

Check first

  • The sump holds 2.7 litres with filter; check the level and look for leaks every visit.
  • DPF cars need a run of at least 30 km monthly at motorway speed.
  • Oil: 5W-30 MB 229.51 low-SAPS, changed every 7,500 km.
  • Replace the balance-shaft chain and tensioner together with the main timing chain.
  • Let the engine idle briefly after hard driving to protect the turbo.

Engine overview

Manufacturer
Mercedes-Benz (Smart)
Displacement
0.8 L
Configuration
I3
Power
41-45 hp
Torque
110 Nm
Production years
2007-2014
Fuel type
Diesel

Vehicles with this engine

Smart ForTwo W451 CDI (2007-2014)

Known failures & weak points

Common rail injectors on the OM660 work at a high duty cycle for their small size and can become sticky, causing hard starting, smoke and rough idle. Return-flow test all three injectors and replace failed units as needed.
Short city trips prevent full DPF regeneration on the active-regen OM660, causing excessive soot loading. Perform forced regeneration via diagnostic tool, and ensure a monthly motorway run of at least 30 km.
The OM660's small turbocharger spins at very high RPM for its output and is vulnerable to oil-feed restriction or abrupt shutdown after hard use, which can cause early bearing wear. Let the engine idle briefly before shutdown after sustained hard driving.
The OM660's timing chain and tensioner can wear and rattle at higher mileage; replace the chain, guides and tensioner as a kit when noise is confirmed.
The small EGR passage on the OM660 clogs readily with soot in city use; a stuck-open valve causes white smoke and power loss. Clean or replace the valve as needed.
The W451's Softip automated-clutch actuator can wear and fail, causing jerky engagement and fault codes. Replace the clutch and actuator motor and recalibrate via diagnostic tool.
The OM660 uses a balance shaft with its own secondary chain and tensioner, which can wear independently of the main timing chain; inspect and replace at the same time as the main chain service to avoid a return visit.

Common torque specifications

Main Bearing Caps Nm 55 Nm + 90° — TTY, replace bolts (single-use) unconfirmed
Connecting Rod Nm 15 Nm + 90° — TTY, replace bolts (single-use) unconfirmed
Cylinder Head Nm 25 Nm + 90° + 90° — TTY, replace bolts (single-use) unconfirmed
Injector Clamp Nm 22 unconfirmed
Oil Drain Plug Nm 25 unconfirmed
Wheel Bolts Nm 110 unconfirmed

Figures marked unconfirmed could not be cross-checked against a workshop source. Verify against the vehicle’s own documentation before tightening.

Workshop procedures for this engine

Step-by-step procedures from the workshop database.

Service intervals

Oil Change Km 7500
Oil Spec 5W-30 MB 229.51 (low-SAPS for DPF)
Fuel Filter Km 30000
Air Filter Km 20000
Coolant Years 4
Gearbox Oil Km 60000

Special tools

  • Smart XENTRY or iCarsoft MB II for DPF regen and injector coding
  • OM660 TDC pin set (3-cyl specific)
  • Common rail pressure gauge (1600 bar rated)
  • Injector return flow test kit (Bosch KIT 0 986 610 ...)
  • Clutch actuator calibration cable adapter

Pro tips from the field

The OM660 CDI is surprisingly robust for its size — most failures are maintenance-related (DPF, EGR) rather than inherent design flaws
The OM660 has a small oil capacity - check oil level regularly, since a small leak or consumption quickly puts the engine at risk.
Injector coding is MANDATORY after replacement — each OM660 injector has a calibration code (IMA code) that must be entered via XENTRY; without coding the engine runs poorly
DPF cars must see a motorway run of 30+ km at least monthly — these are city cars driven in cities, which is exactly the wrong use pattern for diesel; consider petrol version for pure city use
After a highway run, let the OM660 idle briefly before shutdown - its small turbo is more sensitive to heat soak than larger units.

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Who makes these pages, and how

TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.

The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.

Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.

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Workshop data on this page last updated 14 Oct 2026.