OM656 vs 2.2 HDi: which engine is more reliable?

According to our risk index, the OM656 carries less risk than the 2.2 HDi: 39/100 versus 48/100 (both moderate risk). The OM656 has 2 documented serious faults, the main one being «Leak in the vacuum-driven coolant pump (fire risk)»; the 2.2 HDi has 3 documented serious faults, the main one being «DPF clogging with additive, especially on the 128-138 hp version».

Risk index

OM656

Moderate risk · 2 serious faults

Lower risk

Risk index

2.2 HDi

Moderate risk · 3 serious faults

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

Reviewed on 9 October 202618 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 2.2 HDi reliable?

This is a diesel derived from the 2.0 HDi that PSA and Ford shared in large saloons and MPVs (407, 607, 807, C5, C6, C8) and that Land Rover and Ford used under their own names (TDCi, TD4, SD4) in the Mondeo IV, the Freelander 2 and the first Evoque. According to fiches-auto it does not suffer chronically from the turbo or dual-mass flywheel problems of smaller HDi engines, but the 128-138 hp version does have a recurring problem of DPF clogging.^{[9][10][11][12]}

See the 4 of the 2.2 HDi faults

Side-by-side comparison

Comparison of OM656 and 2.2 HDi
Item	OM656	2.2 HDi
Technical data
Type	Engine	Engine
Fuel	Diesel	Diesel
Displacement	2,925 cm³	2,179 cm³
Timing	Chain	Timing belt (dry)
Power	272–367 hp	128–204 hp
Production	since 2017^[1][2][13]	2000–2015^{[9][11][14][15][16]}
Reliability
Risk index (what is it?)	39Moderate risk	48Moderate risk
Documented faults	4	4
Of high or critical severity	2	3
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: DPF clogging with additive, especially on the 128-138 hp version High severity: Turbo faults, somewhat more frequent on the sequential twin-turbo versions High severity: Piezo injector wear and failure
Most expensive documented repair	No reliable data	No reliable data
Which versions to buy
BuyRecommended versions	OM656 3.0 diesel with electric assistance (D 30, from 2023)^[4][5][7]	2.2 HDi 150-156 (single variable-geometry turbo, 2006-2012)^[17][18]
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]	2.2 HDi 128-138 (DW12 TED4, single turbo, 2000-2006)^[12] 2.2 HDi 170-175 twin-turbo (DW12 BTED4, 2005-2010)^[12][15] 2.2 HDi 190-204 twin-turbo (DW12 C, 2010-2015)^[15]
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

2.2 HDi

See the 12 models with the 2.2 HDi

Other comparisons

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With the 2.2 HDi

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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
PSA EW/DW engineWikipedia (inglés) · Other source · consulted 27 September 2026
Ford MondeoWikipedia (francés) · Other source · consulted 27 September 2026 · in French
Land Rover FreelanderWikipedia (francés) · Other source · consulted 27 September 2026 · in French
Essai, avis et fiabilité des 2,2 HDI 136 chevauxFiches-Auto · Motoring press · consulted 27 September 2026 · in French
Mercedes-Benz S-Class (W222)Wikipedia · Other source · consulted 9 October 2026
Range Rover EvoqueWikipedia (inglés) · Other source · consulted 27 September 2026
Essai, avis et fiabilité des 2,2 HDI 204 chevauxFiches-Auto · Motoring press · consulted 27 September 2026 · in French
Essai Citroën C5 Exclusive + 2.2 HDI 200 TourerActu Automobile · Motoring press · published 2011 · consulted 27 September 2026 · in French
Essai Peugeot 4007 2.2 HDi DCS 6Caradisiac · Motoring press · published 7 April 2010 · consulted 27 September 2026 · in French
Citroën C-CrosserWikipedia (español) · Other source · consulted 27 September 2026 · in Spanish