Mercedes-Benz OM646 (2.2 CDI de 4 cilindros) and su antecesor OM611Particulate filter (DPF/FAP)Engine sensors
Particulate filter (DPF) sensor failure on the 2.2 CDI (OM646)
The 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.[1][2][3]
Why this rating?
Low severity: A nuisance or wear. It does not immobilise the car or damage other parts.
Frequency occasional: A single specialist German source on the W203, which does document other OM646 weak points in detail (oil cooler, EGR), describes particulate filter sensor defects as "frequent" in its own words; we have not found a second independent source confirming it, so on our scale we rate it more conservatively as "occasional" until we have an additional reference.[1]
Symptoms
- Particulate filter warning light or message triggered by a sensor fault, not necessarily because the filter is clogged with soot.[1]DPF warning light: other faults that cause it · Garage soon
- Loss of power if the control unit enters protection mode because it is not receiving a reliable reading from the sensor.[1]Limp mode: other faults that cause it · Garage soon
Why it happens
The particulate filter's differential pressure sensor (and on some units the temperature sensor) fails over time, which the German source consulted describes as a frequent defect of the OM646.[1]
If it is not repaired: A faulty sensor does not damage the engine by itself, but it can stop the control unit from managing the filter's regenerations properly and makes it harder to pass the emissions inspection if the warning light stays on.[1]
Affected cars and years
It affects only the OM646, which was the first in the family to offer a particulate filter (from mid-2003); the OM611 did not have one.[2][3]
| Version | Years | Codes |
|---|---|---|
| OM646 pre-EVO (2002-2007, Euro 3/4, 88-150 hp) | 2002–2007 | OM 646 DE22 LAOM 646 DE22 LA R |
| OM646 EVO (2006-2009, up to 170 hp) | 2006–2009 | OM 646 DE22 LA EVO |
Models fitted with the affected versions
Mercedes-Benz
- Mercedes-Benz Clase C W2032003–2007
- Mercedes-Benz Clase C W2042007–2009
- Mercedes-Benz Clase E W2112002–2009
- Mercedes-Benz Sprinter 9062006–2009
- Mercedes-Benz Vito W6392003–2010
How much it costs to repair
Includes: Replacement of the particulate filter sensor.[1]
The source consulted gives no euro figure for the sensor replacement; nor have we found a specific price for Spain.
Prices in Spain, including VAT. A workshop hour costs on average €38–66 at independent garages and €77–134 at dealerships in Spain, depending on the region and the brand. How we calculate costs
How to check for it before buying a used car
- Check in the paperwork, or by asking an official dealer, whether this specific unit has a factory-fitted particulate filter: according to a German source, not all units of the period were fitted with one.[1]
- Ask for a code reading focused on the emissions control system and check that there are no warnings relating to the particulate filter.[1]
Parts needed
The part or kit that fixes this fault, according to the sources.
Particulate filter differential pressure sensor
Tells the control unit how clogged with soot the filter is so it can schedule regenerations; if it fails, the whole part is replaced.
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Recalls, campaigns and claims
As of 27 September 2026, we have no record of recalls, campaigns or extended manufacturer warranties for this fault. Check with an official dealer using the chassis (VIN) number: they will tell you whether the car has any outstanding campaign.
What owners say
Frequently asked questions
Do all OM646 units have a particulate filter?
Not necessarily: it was offered from mid-2003, but a specialist German source points out that some units of the period were sold without it from the factory.[1][3]
Does the OM611 also have this problem?
No: the OM611 predates the introduction of the particulate filter in this engine family, so this fault affects only the OM646.[2][3]
Does a sensor fault mean the filter is ruined?
Not necessarily: it may be just the sensor, which is replaced separately from the physical filter.[1]
What can you do now?
We will put you in touch with a partner only if you authorise it in the form.
Other 2.2 CDI (OM646) faults
- High 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.
- Medium 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.
- Medium 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.
- Medium 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.
- Low 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
More faults with the particulate filter on other engines and cars
- High severityFrequency: Very frequentOM651EGR and particulate filter clogging, and emissions software updatesThe particulate filter and EGR clog up with short journeys, as on any diesel with these systems. In addition, Germany's KBA required software updates on several models with this engine between 2018 and 2021 because of a function that reduced EGR outside a temperature range.Repair (garage): €800–€2,500
- High severityFrequency: Common1.3 MultijetIncomplete particulate filter regenerations and oil dilutionIn heavy urban use, with short journeys that do not let the particulate filter regeneration finish, unburnt diesel passes into the sump and dilutes the oil; the level can rise on the dipstick and the oil loses its ability to lubricate. Repeated many times, it speeds up engine wear.
- High severityFrequency: Common2.0 HDiDPF clogging on additive-type systems (Eolys/cerine)The additive-type diesel particulate filter (DPF) of the 2.0 HDi clogs relatively easily on short journeys, especially on the 107/110 and 136-140 hp versions. The anti-pollution warning light comes on and, if ignored, the car loses power and may end up needing a new DPF.
- High severityFrequency: Common1.6 and 2.0 MultiJet IISaturated diesel particulate filter (DPF) from incomplete regenerationsIn urban use with short journeys, the particulate filter does not manage to complete its regeneration and becomes saturated; garages recommend a weekly motorway run to avoid it. The filter itself is among the weak points flagged in the 1.6 and 2.0 MultiJet II after a certain mileage.
- High severityFrequency: Common2.0 Ingenium diéselFuel dilution of the oil linked to particulate filter regenerationsYes: on short trips and in urban use, the Ingenium diesel's particulate filter does not always complete regeneration, and some of the diesel injected to burn off the soot ends up mixing with the engine oil, which reduces its ability to lubricate.
- High severityFrequency: CommonMZR-CDOil dilution from leaking injector seals and DPF regenerationsOn the 2.0 and 2.2 MZR-CD, injector seals that age badly and incomplete particulate filter regenerations on short journeys can let unburnt diesel into the sump, diluting the oil and leaving the engine with less lubrication.
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Sources
Every fact on this page links to its source. If you find an error, let us know.
- Mercedes C-Klasse W203 – Typische Probleme & SchwachstellenGebrauchtwagenberater · Motoring press · consulted 27 September 2026 · in German
- Mercedes-Benz OM 646/OM 647/OM 648Wikipedia (alemán) · Other source · consulted 27 September 2026 · in German
- Mercedes-Benz W203Wikipedia (alemán) · Other source · consulted 27 September 2026 · in German