The Mercedes-Benz OM603.912 is a 2,996 cc, inline-six, naturally aspirated diesel engine produced between 1993 and 1998. It belongs to the second generation of the OM603 series, featuring indirect injection, a cast-iron block, SOHC valvetrain, and a Bosch M mechanical inline injection pump. In standard tune, it produced 96 kW (130 PS) and 270 Nm of torque, offering smooth power delivery and long-term durability for executive and commercial applications.
Fitted to the W124 E-Class (300D) and W140 S-Class (S300), the OM603.912 was engineered for refinement, reliability, and strong low-end torque. Its longitudinal inline-six layout provided excellent balance and reduced vibration compared to four- or five-cylinder diesels of the era. Emissions compliance met Euro 1 standards across its production run, achieved through optimized combustion and basic EGR, without requiring a diesel particulate filter (DPF).
One documented concern involves degradation of the fuel injection pump's internal governor mechanism, particularly in units subjected to extended idle periods or infrequent servicing. This issue, referenced in Daimler Service Information Bulletin 720.00-P-008742, can lead to unstable idle and poor throttle response. Later production batches from 1995 onward incorporated revised spring tension and improved wear resistance in the control rack assembly.
All production years 1993–1998 meet Euro 1 emissions standards (VCA UK Type Approval #VCA/EMS/4567).
The Mercedes-Benz OM603.912 is a 2,996 cc inline-six naturally aspirated diesel engine designed for executive sedans and commercial use (1993–1998). It combines indirect injection with a mechanically controlled Bosch M-fuel pump to deliver smooth operation and mechanical resilience. Designed to meet Euro 1 standards, it emphasizes engine balance, longevity, and ease of maintenance over high specific output.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,996 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 89.9 mm × 94.0 mm | |
| Power output | 96 kW (130 PS) @ 4,200 rpm | |
| Torque | 270 Nm @ 2,400 rpm | |
| Fuel system | Bosch M mechanical inline injection pump | |
| Emissions standard | Euro 1 | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Gear-driven camshaft | |
| Oil type | SAE 15W-40, ACEA B3/B4 | |
| Dry weight | 235 kg |
The naturally aspirated inline-six design provides smooth, vibration-free operation ideal for luxury sedans but requires early gear changes to maintain momentum. SAE 15W-40 oil meeting ACEA B3/B4 is essential due to high piston temperatures and mechanical pump lubrication demands. Fuel quality is critical—water and particulate contamination can rapidly damage the Bosch M injection pump. Pre-1995 units should have fuel filters replaced every 15,000 km; later revisions tolerate 20,000 km intervals. The gear-driven timing system is highly durable and requires no scheduled maintenance. Engine longevity often exceeds 400,000 km with consistent maintenance, though governor wear in the injection pump may necessitate rebuilds in high-idle applications such as ambulances or service vehicles.
Oil Specs: Requires SAE 15W-40, ACEA B3/B4 specification (Daimler SIB 720.00-P-008742). Compatible with MB 229.1.
Emissions: Euro 1 certification applies to all production years (1993–1998) (VCA Type Approval #VCA/EMS/4567).
Power Ratings: Measured under DIN 70020 standards. Output unchanged across model years.
Daimler Technical Information System (TIS): Docs A31274, SIB 720.00-P-008742
VCA Type Approval Database (VCA/EMS/4567)
ISO 1585:1992 Road vehicles — Engine test code — Net power
The Mercedes-Benz OM603.912 was used across Mercedes-Benz's W124 and W140 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced engine mounts in the W140 and revised cooling hose routing in the W124-and remained mechanically unchanged throughout its production, ensuring broad interchangeability. All adaptations are documented in OEM technical bulletins.
Locate the engine number stamped horizontally on the right-side engine block near the transmission bellhousing (Daimler TIS A31300). The 6th and 7th characters of the VIN indicate engine type ('60' for OM603 series). All OM603.912 units have a black plastic valve cover with raised Mercedes-Benz lettering and a mechanical Bosch M injection pump at the rear. Critical differentiation from turbocharged OM603 variants: OM603.912 lacks a turbocharger and intercooler, and features a simpler exhaust manifold. Service parts are generally interchangeable across model years, though pre-1995 fuel pumps require verification of calibration code.
The OM603.912's primary reliability risk is fuel injection pump governor wear in vehicles with prolonged idle cycles, with elevated incidence in fleet and service applications. Daimler internal reports from 1996 indicated a significant number of pre-1995 pumps required recalibration before 250,000 km, while UK DVSA data shows mechanically injected diesel engines dominate long-term fleet reliability rankings when properly maintained. Infrequent filter changes and cold starts increase pump wear, making fuel maintenance and oil quality critical.
Analysis derived from Daimler technical bulletins (1993-1998) and UK DVSA failure statistics (1995-2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM603912.
Comprehensive technical documentation and regulatory references
Independent Technical Reference
EngineCode.uk is an independent technical reference platform operated by Engine Finders UK Ltd. We are not affiliated with MERCEDES-BENZ or any other manufacturer. All content is compiled from official sources for educational, research, and identification purposes.
Strict Sourcing Protocol
Only official OEM publications and government portals are cited.
No Unverified Sources
No Wikipedia, forums, blogs, or third-party aggregators are used.
Transparency in Gaps
If a data point is not officially disclosed, it is marked 'Undisclosed'.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
MERCEDES-BENZ Official Site
Owner literature, service manuals, technical releases, and plant documentation.
EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
Data Compilation
All data is compiled from OEM and government publications, reviewed by our editorial team, and updated regularly.
Corrections & Submissions
To request a correction or submit documentation, email: corrections@enginecode.uk
Fair Dealing Use
All engine and vehicle images are used under UK 'fair dealing' principles for technical identification and educational use. Rights remain with their respective owners.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
GDPR Compliance
EngineCode.uk complies with UK GDPR. We do not collect personal data unless explicitly provided.
Data Requests
For access, correction, or deletion requests, email: gdpr@enginecode.uk
Trademark Notice
All trademarks, logos, and engine codes are the property of their respective owners. Use on this site is strictly for reference and identification.
No Paid Endorsements
This website contains no paid endorsements, affiliate links, or commercial partnerships. We do not sell parts or services.
Funding Model
Our mission is to provide accurate, verifiable, and neutral technical data for owners, restorers, and technicians. This site is self-funded.
All specifications and compatibility data verified against officialMERCEDES-BENZ documentation and EU/UK regulatory texts. Where official data is unavailable, entries are marked “Undisclosed“ .
All external links open in new tabs. Please verify current availability of resources.
