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Mercedes OM626 Engine (1.6 L Diesel)
The Mercedes OM626 is a 1.6 L inline-4 diesel engine (closely related to the Renault R9M) developed for the W205 C-Class (2014–2018).
Compact yet efficient, it delivers 114 hp and 192 lb-ft of torque enough for daily driving, while returning around 50 mpg and meeting Euro 6 emissions standards with advanced EGR, DPF, and SCR technology.
But like most modern diesels, the OM626 comes with its own set of quirks: EGR clogging, DPF blockages, and turbo seal issues if neglected.
This guide covers specs, strengths, common problems, fixes, and maintenance tips to keep the OM626 reliable.
For a complete overview of all Mercedes powerplants, visit our Mercedes Engine Types Hub.
Quick Facts: OM626 at a Glance
- Type: 1.6 L inline-4, common-rail diesel
- Origin: Based on Renault R9M, modified by Mercedes
- Applications: Mercedes-Benz C-Class W205 (2014–2018)
- Output: 114 hp / 192 lb-ft
- Fuel System: Common rail (1600 bar)
- Turbo: Variable-geometry turbocharger (VTG)
- Emissions tech: EGR + DPF + SCR (AdBlue)
- Claimed economy: ~50 mpg, ~104 g/km CO₂
OM626 Engine Specifications
| Spec | Details |
|---|---|
| Displacement | 1598 cc |
| Bore × Stroke | 80 × 79.5 mm |
| Block | Cast-iron with aluminum alloy head |
| Pistons | Steel pistons (Mahle) with low-tension rings |
| Valvetrain | DOHC, 16 valves |
| Injection pressure | Up to 1600 bar |
| Turbo | VTG (variable turbine geometry) |
| Power | ~114 hp |
| Torque | ~260 Nm (192 lb-ft) |
| Emissions | Euro 6 |
Key Design Features
- – Steel pistons: Stronger than aluminum, better thermal efficiency.
- – Low-friction internals: Improves fuel economy.
- – Variable-geometry turbo: Optimized boost across RPMs.
- – Start/stop system: Saves fuel in city driving.
- – Advanced aftertreatment: EGR + DPF + SCR for Euro 6 compliance.
OM626 Engine Problems & Troubleshooting
Despite its efficiency, the OM626 has a few predictable weak points:
| Problem | Symptoms | Recommended Fix |
|---|---|---|
| EGR valve blockage | Loss of power, limp mode, rough idle | Clean or replace EGR valve; periodic motorway runs help |
| DPF clogging | Limp mode, rough running, high fuel use | Regeneration on long drives; forced regen/clean at workshop |
| Turbo/seal failures | Oil in intake, smoke, limp mode | Inspect turbo, charge pipes, PCV separator; replace seals/turbo if needed |
| Oil leaks (valve cover) | Visible oil on intake/hoses | Replace gasket or crankcase breather |
| Carbon build-up (intake) | Throttle hesitation, rough idle | Walnut-blast or intake clean every ~60k mi |
Related case studies:
Loss Of Power In Car While Driving : Case Study & Solution
Maintenance & Care Checklist
| Task | Interval | Notes |
|---|---|---|
| Oil & filter change | 15–20k km (10–12k mi) | Use MB 229.51 low-SAPS synthetic |
| Fuel filter | 30–40k km | Prevents injector stress |
| EGR & intake check | 60k km | Clean to avoid clogging |
| DPF regeneration | Ongoing | Include long motorway drives |
| Turbo hoses & PCV | Every service | Replace at first sign of leaks |
| Valve cover gasket | Inspect each service | Replace if sweating oil |
Pro tip: Most limp mode events are EGR-related. Cleaning early prevents breakdowns.
Fuel Economy & Emissions
- – Combined economy: ~50 mpg
- – CO₂ emissions: ~104 g/km
- – Emissions systems: Start/stop, DPF, SCR (AdBlue)
- – Driving tip: Short-trip use accelerates EGR/DPF clogging. Add highway runs weekly.
Applications: Which Mercedes Models Have OM626?
- Mercedes C-Class (W205, 2014–2018) – C180d / C200d
OM626 vs. Other Mercedes Diesels
| Feature | OM626 (1.6) | OM651 (2.1) | OM654 (2.0, successor) |
|---|---|---|---|
| Output | 114 hp | 136–204 hp | 150–245 hp |
| Block | Cast iron | Cast iron | All-aluminum |
| Pistons | Steel | Aluminum | Steel |
| Issues | EGR, DPF, oil leaks | Timing chain, injectors | Fewer known (newer design) |
| Best use | City + light duty | Mixed driving, higher torque | Efficiency + emissions compliance |
OM626 Reliability & Verdict
The OM626 is reliable when maintained, but it’s not a high-mileage warrior like the larger OM651 or OM642. Its steel pistons, compact design, and Euro 6 compliance make it a clever commuter engine.
- – Pros: Fuel economy, modern tech, lower CO₂.
- – Cons: Sensitive to short trips, limp mode from EGR/DPF, modest power output.
For owners: Stick to good oil, proper regen cycles, and regular intake/EGR care and the OM626 will serve faithfully.
FAQ
Q1: Is the Mercedes OM626 reliable?
Yes, if serviced correctly. Most issues (EGR clogging, DPF, turbo leaks) stem from short trips and poor maintenance.
Q2: What cars have the OM626?
The OM626 was used in the Mercedes-Benz C-Class (W205) from 2014–2018 in C180d and C200d trims.
Q3: What’s the oil capacity of OM626?
Around 5.3–5.5 liters with filter, using MB 229.51 spec synthetic.
Q4: OM626 vs OM654: which is better?
The newer OM654 is more efficient, powerful, and has fewer emissions issues. The OM626 is simpler but less robust for high mileage.
For a complete overview of all Mercedes powerplants, visit our Mercedes Engine Types Hub.
Author
Written by Mercedes Expert
With years of hands-on experience diagnosing and repairing Mercedes-Benz systems, he brings technical depth and practical case studies to help car owners, technicians, and enthusiasts troubleshoot complex automotive issues. His work focuses on clear repair guides, OEM-level procedures, and knowledge-sharing to empower both professionals and drivers.
Last Updated: September 2025
