2.2 CDI (OM646) engine: faults and reliability

• OM611 (predecessor, 2.2 CDI, 1998-2006)

  1998–2006 · 82–143 hp · OM 611, OM611 DE22

  With caution

  A specialist German site describes it as the most reliable of the family, capable of exceeding 500,000 km with correct maintenance; however, a French source compiling owner testimonies places the injectors as the most fragile point precisely on the 143 hp version that corresponds to the OM611. You should check the condition of the injectors and the EGR valve before buying.^[2][4]

• OM646 pre-EVO (2002-2007, Euro 3/4, 88-150 hp)

  2002–2007 · 88–150 hp · OM 646 DE22 LA, OM 646 DE22 LA R

  With caution

  It shares the documented weak points of the OM646 family: leaks at the injector seals, fouling of the EGR valve (more pronounced in urban use), particulate filter sensor failures and a short-lived water pump on some units. None of these problems has led to an official manufacturer campaign according to the sources consulted, but you should check the maintenance history.^[2][3][4]

• OM646 EVO (2006-2009, up to 170 hp)

  2006–2009 · 150–170 hp · OM 646 DE22 LA EVO

  With caution

  It is the highest-output version and the one that concentrates the most testimonies of injection and water pump failures according to a French source collecting owner reports, possibly because it demands more of the engine. There is no sign that the EVO revision corrected the family's known weak points.^[4]

Buy: No known serious faults, or they have already been corrected, in this version. With caution: Worth buying if something specific is verified: history, a replaced part or a completed campaign. Avoid: High risk of a serious fault that is hard to check for or prevent.

1. 1High severityFrequency: CommonInjectionInjector seal leak with carbonisation around the seatYes: the copper washer that seals each injector can harden and let combustion gases through, forming a black crust of carbon around it. It is a known fault on Mercedes CDI diesels of this era, with injectors described as fragile on both the OM611 and the OM646.
2. 2Medium severityFrequency: CommonEmissions controlEGR valve clogged or seized by sootYes: the EGR valve on the OM646 (and the OM611) accumulates soot over the miles, especially on short urban journeys, until it seizes. It is one of the faults owners cite most on several power versions, along with the injectors.
3. 3Medium severityFrequency: OccasionalCoolingLeak and premature failure of the water pumpOn the 170 hp version of the OM646 (the highest-output one, 2006-2009), the water pump appears as one of the faults owners cite most, along with leaks from the radiator, hoses and thermostat, according to a specialist French source.
4. 4Medium severityFrequency: OccasionalIgnitionGlow plugs seize and snap when removed on the OM611On Mercedes OM611, OM612 and OM613 diesels, glow plugs can break when loosened, because they stick in the cylinder head through carbon and rust. Hella published a bulletin with a specific procedure to avoid this.
5. 5Low severityFrequency: OccasionalEmissions controlParticulate filter (DPF) sensor failureThe OM646 introduced an additive-free particulate filter from mid-2003, but its sensor fails relatively often according to a specialist German source. Also, not all units of the period were fitted with it at the factory, so you should check whether the specific car has one before assuming a fault.
6. 6Low severityFrequency: RareIntakeFaulty air flow meter on the 220 CDI (OM 611 and OM 646)On the 220 CDI the air flow meter fails in a minority of units: 14 of the 503 opinions collected by fiches-auto. It alters the air/fuel mixture and is cheap to repair.Repair (garage): €100–€300

Severity colours: low, medium, high, critical. How we rate them

Manufacturer

Mercedes-Benz (Daimler)

Family

Familia OM611/OM646 de diésel de 4 cilindros con common rail de Mercedes-Benz (con hermanos de 5 y 6 cilindros, OM647 y OM648, no cubiertos en esta ficha)

Fuel

Diesel

Displacement

2,148 cm³

Cylinders

4

Fuel system

Turbo

Injection

Common rail

Timing

Chain

Power

82–170 hp

Peak torque

400 Nm

Production

1998–2010

Makes

Mercedes-Benz and Chrysler

Technical data^[1][5][6]

1. 1998–2006

   OM611 (predecessor, 2.2 CDI, 1998-2006)

   First generation of Mercedes-Benz's 2.2 CDI, with second-generation common-rail injection. It replaced the OM604 (naturally aspirated, indirect injection) from 1998. On the C-Class W203 it was fitted as the C 200 CDI (85 kW/116 hp) and C 220 CDI (105 kW/143 hp) until the OM646 replaced it in 2003-2004. The E-Class W211, launched in 2002, already used the OM646 from the outset and never used the OM611.^[6][7]

2. 2002–2007

   OM646 pre-EVO (2002-2007, Euro 3/4, 88-150 hp)

   It replaced the OM611 from 2002 (E-Class W211) and 2003 (C-Class W203), and also powered the Vito/Viano W639 from its launch in 2003 and the Sprinter 906 from 2006. From mid-2003 it was offered with an additive-free particulate filter system, approved to Euro 4, although, according to a specialist German source, not all units of the period were fitted with it at the factory. This calibration was kept without the EVO revision on the Vito/Viano and the Sprinter throughout their entire commercial life with this engine.^[1][2][5][7]

3. 2006–2009

   OM646 EVO (2006-2009, up to 170 hp)

   Thorough revision of the OM646 with a lower compression ratio (17.5:1), a new turbocharger and ceramic glow plugs, with up to 125 kW (170 hp). It reached the C-Class W204 on its first units and the E-Class W211 in its facelift, before the OM651 became widespread on both models.^[5]

• Timing chain kit

  • Buy part at Autodoc (affiliate link, opens in a new tab)

• Oil filter

  • Buy part at Autodoc (affiliate link, opens in a new tab)

• Air filter

  • Buy part at Autodoc (affiliate link, opens in a new tab)

• Diesel fuel filter

  • Buy part at Autodoc (affiliate link, opens in a new tab)

• Glow plugs

  • Buy part at Autodoc (affiliate link, opens in a new tab)