OM656 vs 2.3 dCi (M9T): which engine is more reliable?

According to our risk index, the 2.3 dCi (M9T) carries less risk than the OM656: 32/100 versus 39/100 (both moderate risk). The OM656 has 2 documented serious faults, the main one being «Leak in the vacuum-driven coolant pump (fire risk)»; the 2.3 dCi (M9T) has 2 documented serious faults, the main one being «Clogged or broken EGR valve damaging the turbo».

Risk index

OM656

Moderate risk · 2 serious faults

Risk index

2.3 dCi (M9T)

Moderate risk · 2 serious faults

Lower risk

The index (0–100) weights the severity and frequency of the three most serious documented faults. How it is calculated

Reviewed on 9 October 202614 sources How we work

Is the OM656 reliable?

The OM656 is the roughly 3.0-litre in-line six-cylinder diesel with which Mercedes-Benz replaced the OM642 V6 from 2017 in the S-Class, E-Class, CLS, GLE, GLS and G-Class (350 d, 400 d and 450 d). It has few documented faults: the known campaign is the coolant pump one of 2021-2022, and the timing chain recall that circulates belongs to the OM654. Guides warn about the AdBlue/SCR system, the EGR and, in isolated cases, the roller rocker arms, without figures.^{[1][2][3][4][5][6][7][8]}

See the 4 of the OM656 faults

Is the 2.3 dCi (M9T) reliable?

The 2.3 dCi M9T is a van diesel with good durability if maintenance is kept up. The weak points cited are the EGR and the turbo, the injectors, and the particulate filter in urban use; the sources are mostly opinion websites.^[9][10]

See the 5 of the 2.3 dCi (M9T) faults

Side-by-side comparison

Comparison of OM656 and 2.3 dCi (M9T)
Item	OM656	2.3 dCi (M9T)
Technical data
Type	Engine	Engine
Fuel	Diesel	Diesel
Displacement	2,925 cm³	2,300 cm³
Timing	Chain	Chain
Power	272–367 hp	100–180 hp
Production	since 2017^[1][2][11]	since 2010^[9][10][12]
Reliability
Risk index (what is it?)	39Moderate risk	32Moderate risk
Documented faults	4	5
Of high or critical severity	2	2
Worst severity	Critical severity	High severity
Main faults	Critical severity: Leak in the vacuum-driven coolant pump (fire risk) Medium severity: NOx sensor failure and AdBlue (SCR) system warnings Medium severity: EGR valve clogged with soot after short journeys	High severity: Clogged or broken EGR valve damaging the turbo Medium severity: Faulty injectors on the 2.3 dCi Medium severity: Diesel particulate filter (DPF) clogged in urban use
Most expensive documented repair	No reliable data	up to €2,300Clogged or broken EGR valve damaging the turboPublished figure^[9][13]
Which versions to buy
BuyRecommended versions	OM656 3.0 diesel with electric assistance (D 30, from 2023)^[4][5][7]	2.3 dCi 100-125 hp (M9T)^[10] 2.3 dCi 130-145 hp (M9T)^[10]
With cautionVersions to be cautious about	OM656 2.9 diesel 350 d (OM 656 D 29 R SCR, from 2017)^[3][4][5] OM656 2.9 diesel 400 d (OM 656 D 29 SCR, from 2017)^[3][4][5][7]	2.3 dCi 150-180 hp (M9T, some twin-turbo)^[10] 2.3 dCi in the Navara D23 (NP300)^[14]
AvoidVersions to avoid	None	None

Severity of each fault: green, low; amber, medium; red, high; dark red, critical. How we rate them

Cars that each one is fitted to

OM656

See the 11 models with the OM656

2.3 dCi (M9T)

Other comparisons

With the OM656

With the 2.3 dCi (M9T)

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Sources

Every fact on this page links to its source. If you find an error, let us know.

Mercedes-Benz OM656 engineWikipedia · Other source · consulted 9 October 2026
Mercedes-Benz OM 656Wikipedia (alemán) · Other source · consulted 9 October 2026 · in German
Rückruf für OM 656 und OM 654 Motoren wegen KühlmittelpumpeMBpassion · Motoring press · published 9 December 2021 · consulted 9 October 2026 · in German
Mercedes-Rückruf: Kühlmittelprobleme bei DieselautosAUTOHAUS · Motoring press · published 5 January 2022 · consulted 9 October 2026 · in German
DVSA – base de llamadas a revisiónDVSA (Reino Unido) · Other source · consulted 9 October 2026
Mercedes-Benz GLC (X253): Alle typischen Probleme & MängelGebrauchtwagenberater · Motoring press · consulted 9 October 2026 · in German
Mercedes OM656 Diesel: Häufige Probleme, Ursachen & Tipps zur Vermeidung von MotorschädenMBpassion · Motoring press · published 19 February 2026 · consulted 9 October 2026 · in German
Mercedes-Benz OM656 Engine Guide: Reliability, Common Problems & Tuning PotentialEuro Premium Parts · Technical documentation · consulted 9 October 2026
Renault Master III 2.3 dCi 130: fiabilité, pannes et coûtsCarverif · Other source · consulted 5 October 2026 · in French
Fiabilité Renault Master 2.3 dCiCarverif · Other source · consulted 5 October 2026 · in French
Mercedes-Benz S-Class (W222)Wikipedia · Other source · consulted 9 October 2026
Renault Master (tercera generación)Wikipedia · Other source · consulted 5 October 2026
Fiabilité du Renault Master RT 2.3 dCi: analyse complèteCarverif · Other source · consulted 5 October 2026 · in French
Nissan Navara wymaga zmian systemu oczyszczania spalinAutokatalog.pl · Motoring press · published 23 August 2023 · consulted 5 October 2026 · in another language