Mercedes OM651 problems: injectors, timing chain, should you buy one

Mercedes-Benz · Diesel · 2008-2021

Engine codes: OM651 DE 22 LA, OM651 DE 18 LA

The OM651 is Mercedes-Benz's four-cylinder diesel (2.1 litres, plus a 1.8), fitted from 2008 in the C-, E-, GLK- and ML-Class, the A- and B-Class family, the Sprinter, Vito and V-Class, and the Infiniti Q50 2.2d. Its best-known fault is the Delphi piezo injectors on early 220 and 250 CDI engines, which failed early and were later replaced by solenoid injectors. The timing chain sits at the gearbox end, a recall covered a leaking chain-tensioner seal on 2014 builds, and the intake manifold, the EGR valve and a plastic coolant flange are the other known weak points. A later car or van with regular oil changes is a sound buy; an early 220 or 250 CDI needs proof of the injector work.

At a glance

Displacement: 2.1 L (2,143 cc), 4 cylinders; 1.8 L (1,796 cc) in some A-Class, B-Class and CLA models
Timing drive: Gears plus a single roller chain at the back of the engine, on the gearbox side
Charging: Single turbo on the lower outputs, two-stage twin turbo on most versions from 163 PS
Power: About 95-204 PS (badged 180 to 250 CDI or d in cars, 210 to 516 CDI in the Sprinter)
Injectors: Solenoid injectors on the lower outputs; early 170 and 204 PS engines had Delphi piezo injectors, later changed to solenoid injectors
Successor: OM654 (2.0 L), phased in from 2016 in cars and from late 2020 in the Sprinter

Cars with this engine

Make	Models	Years
Mercedes-Benz	C-Class: C 180 to C 250 CDI (W204); C 200 d, C 220 d, C 250 d, C 300 h (W205)	2008-2018
Mercedes-Benz	E-Class: E 200 to E 250 CDI and BlueTEC, E 300 BlueTEC Hybrid (W212, C207/A207)	2009-2017
Mercedes-Benz	GLK 200 to 250 CDI (X204); GLC 220 d, 250 d (X253); ML 250 BlueTEC (W166), GLE 250 d	2009-2019
Mercedes-Benz	A-Class, B-Class, CLA, GLA: 180, 200, 220 CDI and d (W176, W246, C117, X156)	2011-2018
Mercedes-Benz	Sprinter 210 to 516 CDI and BlueTEC (W906), 211 to 516 CDI (W907 until the OM654 took over)	2009-2021
Mercedes-Benz	Vito and Viano (W639); Vito and V-Class V 200 d to V 250 d (W447)	2010-2019
Infiniti	Q50 2.2d	2013-2020

Known problems

Early Delphi piezo injectors failing

What happens

Soon after launch, the Delphi piezo injectors in the stronger 170 PS (220 CDI) and 204 PS (250 CDI) engines began to fail, sometimes at around 50,000 km, and the engine dropped into limp mode. Mercedes traced it to production faults at the supplier, replaced injectors, moved production to solenoid injectors from 2010-2011 and converted many earlier cars in a free service action. The lower-output versions had solenoid injectors from the start and were not affected.

Symptoms

Check-engine light and limp mode with reduced power
Juddering or uneven running
Higher fuel consumption

When

220 CDI and 250 CDI engines built 2008-2011; failures were reported from around 50,000 km

Fitted cost

from €250 to €650

The fix

Check which injectors are fitted and whether the conversion was done. A failed injector is replaced or reconditioned and coded to the engine control unit; a set of four costs roughly €800-1,600.

Related fault codes

P0201 P0202 P0203 P0204 P0300

Sources: autobild.de, de.wikipedia.org, autokult.pl, auto-swiat.pl, carsuk.net

Timing chain stretch and tensioner seal leak (recall)

What happens

The OM651 drives its camshafts through gears and a single roller chain at the back of the engine, on the gearbox side. A worn tensioner lets the chain stretch, which shows as clatter on a cold start. Separately, Mercedes recalled OM651 cars and vans built between February and November 2014 (and some older ones fitted with a replacement engine) because the seal at the chain tensioner could let oil escape, in extreme cases letting the chain come loose. On a 2014 car or van, ask a Mercedes dealer to confirm on the VIN that the work was done.

Symptoms

Clattering or rattling for a few seconds after a cold start
Oil level dropping, oil traces at the back of the engine near the gearbox
Check-engine light with a crankshaft/camshaft correlation code

When

Chain wear mostly at high mileage, often from about 150,000 km; the tensioner-seal recall covers engines built February to November 2014

Fitted cost

from €1,500 to €2,500

The fix

Replace the chain, tensioner and guides. Depending on the model the engine or gearbox comes out, although some specialists do it in the car with special tools. Under the recall, the tensioner seal is replaced free of charge.

Related fault codes

P0016 P0017 P0340 P0341

Sources: autobild.de, autoservicepraxis.de, de.wikipedia.org, auto-swiat.pl, mbpassion.de, planmycamper.de

Intake manifold flaps and cracked manifold

What happens

The plastic intake manifold carries flaps that control how air enters the cylinders. The flap mechanism can fail, and the manifold can crack along its seams, which lets boost pressure escape. The manifold is normally replaced as one unit.

Symptoms

Hissing under load
Loss of power, sometimes limp mode
Soot marks around the intake manifold
Check-engine light with a boost-pressure code

When

Any age; more likely at higher mileage

Fitted cost

from €300 to €750

The fix

Replace the intake manifold with its flaps and actuator, and clear any stored codes after a test drive.

Related fault codes

P0299

Sources: auto-swiat.pl, planmycamper.de, mbpassion.de

Coked EGR valve

What happens

Soot builds up in the EGR valve and the intake passages, especially on cars and vans that idle a lot or cover short, slow trips. A coked valve sticks, the engine gets the wrong mix of fresh air and exhaust gas, and it runs rough and loses power.

Symptoms

Rough idle
Noticeable loss of power
Check-engine light with an EGR code

When

Mostly on engines used for short trips, city driving or long idling

Fitted cost

from €150 to €600

The fix

Clean the valve and the intake passages, or replace the valve; the new valve may need a relearn with Mercedes-capable software.

Related fault codes

P0400 P0401 P0404

Sources: mbpassion.de, planmycamper.de

Leaking plastic coolant flange

What happens

A plastic coolant flange on the cylinder head can warp or turn brittle with repeated heating and cooling and start to leak. The coolant often collects out of sight or runs down the back of the engine and the gearbox, so the level falls without an obvious puddle. Left alone, a low coolant level can lead to overheating.

Symptoms

Coolant level dropping between checks
Sweet coolant smell after a drive
Dried coolant traces around the cylinder head or on the gearbox

When

Any age; more common as the engine gets older

Fitted cost

from €100 to €300

The fix

Replace the flange and its seal, then refill and bleed the cooling system.

Sources: planmycamper.de, mbpassion.de

What an OBD2 reader can and cannot show

A generic OBD2 reader can show

Stored and pending engine codes such as P0016, P0017, P0340 and P0341 (crankshaft and camshaft timing), P0201-P0204 (injector circuits) and P0300 (misfire)
Boost and EGR codes such as P0299, P0400, P0401 and P0404, plus particulate filter codes such as P2002, P244A and P244B
The freeze-frame snapshot saved with a code: rpm, load, coolant temperature and speed at the moment it set
Live coolant temperature, to spot a car or van that loses coolant or runs hot under load
Live intake manifold pressure (MAP) and airflow (MAF), which show whether the engine builds boost and breathes normally
Readiness monitors: several incomplete monitors on a car for sale suggest the codes were cleared recently

Needs manufacturer-level software

Per-cylinder injector correction values, which need XENTRY or a Mercedes-capable tool and show a failing injector before a code sets
Which injector type is fitted: piezo or solenoid is a question for the paperwork or a look under the engine cover
How far the timing chain has stretched before a timing code sets, which needs a cold-start listen or Mercedes-specific data
Whether recall work such as the tensioner seal has been done: a Mercedes dealer checks that on the VIN
EGR valve commanded versus actual position, soot load in grams and regeneration count of the particulate filter (manufacturer-extended data)
Coolant or oil leaks, which need a visual inspection

Buying checklist

Note the exact version (for example C 220 CDI or Sprinter 316 CDI) and the build date: 170 and 204 PS engines from 2008-2011 are the injector risk.
On a 2008-2011 220 or 250 CDI, ask for invoices showing replaced injectors or the service conversion. Solenoid injectors need a fuel return line (a black plastic pipe on the injectors), which the original piezo injectors did not have.
Start the engine fully cold (parked overnight, bonnet cold) and listen for chain clatter in the first seconds.
On a car or van built in 2014, ask a Mercedes dealer to confirm on the VIN that the chain-tensioner seal recall was done.
Check the coolant level and look for dried coolant around the cylinder head and down the gearbox, and for oil at the back of the engine.
Look for oil changes at regular, short intervals (on hard-working vans about every 15,000 km) rather than stretched ones.
Read stored and pending codes and the readiness monitors before the test drive.
On the test drive, accelerate firmly in a higher gear: listen for hissing from the intake and watch for sudden loss of power or limp mode.

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Frequently asked questions

Is the Mercedes OM651 a good engine?

It is economical and long-lived when serviced well, but it has well-documented weak points: the early piezo injectors on the 220 and 250 CDI, the timing chain and tensioner at the back of the engine, the intake manifold, the EGR valve and a coolant flange that can leak. Engines built from about 2012 with regular oil changes have a much better record than the first ones.

Which OM651 engines have the injector problem?

The stronger 170 PS (220 CDI) and 204 PS (250 CDI) versions built from 2008 to about 2011 with Delphi piezo injectors. Mercedes moved to solenoid injectors from 2010-2011 and converted many earlier cars in a free service action. The lower-output versions, such as the 200 CDI, had solenoid injectors from the start.

How can I tell whether an OM651 has piezo or solenoid injectors?

Check the invoices for an injector replacement or the service conversion first. Under the engine cover, solenoid injectors have a fuel return line, a black plastic pipe on the injectors, which the original piezo injectors did not have. If in doubt, a Mercedes workshop can check the fitted parts on the VIN.

Where is the OM651 timing chain and what does it cost to replace?

The chain sits at the back of the engine, on the gearbox side, so the engine or the gearbox usually has to come out. At an independent workshop a chain, tensioner and guides typically cost about €1,500-2,500 fitted; dealer prices are higher. If the chain has jumped, the engine damage costs far more.

Was there a recall on the OM651 timing chain?

Yes. Mercedes recalled OM651 cars and vans built between February and November 2014, plus some older vehicles fitted with a replacement engine, because the seal at the chain tensioner could leak oil. The seal was replaced free of charge. On a 2014 vehicle, ask a Mercedes dealer to confirm the work on the VIN.

Which cars have the OM651 engine?

Mainly the Mercedes C-Class (W204, W205), E-Class (W212), GLK, GLC, ML 250 and GLE 250 d, the A-Class, B-Class, CLA and GLA diesels up to about 2018, the Sprinter (W906 and early W907), the Vito, Viano and V-Class, plus the Infiniti Q50 2.2d. It was badged 180 to 250 CDI, later 200 d to 250 d.

Sources

Last updated: 2026-09-26