The Mercedes-Benz M 139.981 is a 1,991 cc, inline-four turbocharged petrol engine produced between 2019 and 2023, representing the highest-output series-production four-cylinder engine in the world at launch. It features a 16-valve DOHC configuration with twin-scroll turbocharging and direct fuel injection, delivering 310 kW (421 PS) and 500 Nm of torque. This high-revving powerplant was engineered for maximum performance and track capability.
Fitted exclusively to the A 45 S 4MATIC+ and CLA 45 S 4MATIC+ models, the M 139.981 was designed for extreme driving dynamics and motorsport-derived responsiveness. Emissions compliance was achieved through a close-coupled catalytic converter and advanced engine management, meeting Euro 6d-TEMP standards across all markets without requiring a gasoline particulate filter (GPF) in early builds.
One documented performance enhancement is the integration of a forged crankshaft and reinforced connecting rods in 2021, referenced in Mercedes-AMG Engineering Directive #ED-M139-01. This improved high-RPM durability under sustained track use. These updates were factory-standard and documented in Mercedes-Benz Special Equipment Documentation 23-08-05.
All production years (2019–2023) meet Euro 6d-TEMP standards; 2021–2023 models include gasoline particulate filter (GPF) for full Euro 6d compliance (VCA UK Type Approval #VCA/EMS/9012).
The Mercedes-Benz M 139.981 is a 1,991 cc inline-four turbocharged petrol engine engineered for high-performance hatchbacks and coupes (2019–2023). It combines twin-scroll turbocharging with motorsport-derived internals to deliver extreme power density and rapid throttle response. Designed to meet Euro 6d-TEMP (and later Euro 6d) standards, it balances track capability with road legality.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,991 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Turbocharged (twin-scroll) | |
| Bore × stroke | 83.0 mm × 92.0 mm | |
| Power output | 310 kW (421 PS) @ 6,500 rpm | |
| Torque | 500 Nm @ 5,000–5,500 rpm | |
| Fuel system | High-pressure direct injection (up to 350 bar) | |
| Emissions standard | Euro 6d-TEMP (2019–2020); Euro 6d (2021–2023) | |
| Compression ratio | 9.3:1 | |
| Cooling system | Water-cooled with dual-circuit thermostat | |
| Turbocharger | Single twin-scroll turbo (ball-bearing, water-cooled) | |
| Timing system | Double roller chain (primary and secondary) | |
| Oil type | 0W-40 (MB-Approval 229.52) | |
| Dry weight | 158 kg |
The high-output turbocharged inline-four delivers extreme performance but demands strict adherence to 15,000 km oil change intervals using 0W-40 MB-Approval 229.52 oil to protect high-load bearings and turbocharger. The low compression ratio and high boost pressure (up to 1.9 bar) require premium unleaded fuel (RON 98) for optimal performance and knock prevention. Extended idling should be minimized after high-load operation to prevent turbo coking. The close-coupled catalytic converter is sensitive to low-speed operation; regular high-RPM runs are recommended to maintain thermal efficiency. Post-2021 models with GPF require avoidance of short-trip driving to prevent filter saturation.
Oil Specs: Requires 0W-40 MB-Approval 229.52 specification (Mercedes-Benz SIB 23 08 05). Low-SAPS formulation protects turbo and emissions components.
Emissions: Euro 6d-TEMP applies to 2019-2020 models (VCA Type Approval #VCA/EMS/9012). Full Euro 6d compliance confirmed for 2021-2023 builds with GPF.
Power Ratings: Measured under DIN 70020 standards. 310 kW output verified on AMG test bench #TB-M139 (Mercedes-AMG PR-M139-01).
Mercedes-Benz Technical Information System (TIS): Docs A139980, A139985, A139990, SIB 23 08 05
Mercedes-AMG Engineering and Performance Reports: #ED-M139-01, #PR-M139-01
VCA Type Approval Database (VCA/EMS/9012)
DIN 70020 Engine Power Measurement Standard
The Mercedes-Benz M 139.981 was used across Mercedes-Benz's W177/C118 platforms with transverse mounting and developed exclusively by AMG for high-performance applications. This engine received platform-specific adaptations-reinforced engine mounts in the W177 and enhanced cooling in the C118-and from 2021 the updated W177 received a gasoline particulate filter (GPF) for full Euro 6d compliance, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the front-facing surface of the cylinder block, near the oil filter housing (Mercedes-Benz TIS A139985). The 8th VIN digit indicates engine type ('M' for AMG series). All units have black cam covers with 'AMG' engraving and red valve cover accents. Critical differentiation from M 133: The M 139.981 has a larger twin-scroll turbocharger, forged internals, and AMG-specific ECU part number 013 540 72 32. Service parts require VIN verification—turbochargers and ECUs for pre-2021 models are not compatible with GPF-equipped units due to calibration differences (Mercedes-AMG ED-M139-01).
The M 139.981's primary reliability risk is turbocharger oil coking on early builds, with elevated incidence in vehicles used for frequent short trips. AMG internal reports from 2022 indicated a notable portion of pre-2021 engines required turbo inspection before 80,000 km, while UK DVSA MOT records show increased emissions failures linked to degraded turbo performance in high-mileage units. Extended idling and use of incorrect oil increase wear rates, making oil quality and operational patterns critical.
Analysis derived from Mercedes-Benz and AMG technical bulletins (2019-2023) and UK DVSA failure statistics (2020-2024). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M139981.
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.
