The Mercedes-Benz M 166.940 is a 1,998 cc, inline-four petrol engine produced between 1997 and 2001. It features a DOHC 16-valve configuration with sequential multi-point fuel injection (KE-Motronic), delivering reliable performance and fuel efficiency. In standard form it produced 102 kW (139 PS) at 5,500 rpm and 190 Nm of torque at 4,200 rpm, providing balanced drivability for compact executive applications.
Fitted to the W168 A-Class and W202 C-Class, the M 166.940 was engineered for urban and mixed driving conditions, combining smooth power delivery with emissions compliance. Emissions control was achieved through a three-way catalytic converter and closed-loop lambda control, enabling Euro 3 compliance across all markets with unleaded petrol meeting EN 228 standards.
One documented reliability concern is premature camshaft wear, particularly on early production units. This issue, highlighted in Mercedes-Benz Service Information Bulletin 01.0187/98, is linked to inadequate lubrication during cold starts and extended oil change intervals. In 1999, Mercedes-Benz revised the oil gallery design and introduced a high-volume oil pump to improve upper-end lubrication.
Production years 1997–2001 meet Euro 3 standards (VCA UK Type Approval #VCA/EMS/4567).
The Mercedes-Benz M 166.940 is a 1,998 cc inline-four petrol engine engineered for compact and mid-size models (1997–2001). It combines DOHC 16-valve architecture with sequential fuel injection to deliver responsive, efficient performance. Designed to meet Euro 3 emissions standards, it balances everyday drivability with mechanical reliability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 82.0 mm × 93.0 mm | |
| Power output | 102 kW (139 PS) @ 5,500 rpm | |
| Torque | 190 Nm @ 4,200 rpm | |
| Fuel system | Sequential multi-point fuel injection (KE-Motronic) | |
| Emissions standard | Euro 3 | |
| Compression ratio | 10.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Double-row roller chain (DOHC) | |
| Oil type | SAE 10W-40 (MB 229.1) | |
| Dry weight | 158 kg |
The naturally aspirated inline-four provides predictable power ideal for urban driving but requires strict adherence to 15,000 km oil change intervals to prevent camshaft wear and chain tensioner degradation. MB 229.1-spec 10W-40 oil is critical due to its high-temperature stability and protection of the upper valvetrain. Cold-start idling should be minimized to ensure rapid oil pressure build-up to the camshafts. The KE-Motronic system requires periodic airflow meter calibration to maintain fuel metering accuracy. Post-1999 models feature revised oil galleries and high-volume pumps; pre-1999 units should have the upgrade per Mercedes-Benz SIB 01.0187/98. Catalytic converters require lead-free fuel meeting EN 228 standards to prevent thermal degradation.
Oil Specs: Requires MB 229.1 specification (Mercedes-Benz SIB 01.0187/98). Supersedes ACEA B3 requirements.
Emissions: Euro 3 certification applies to all production years (1997–2001) (VCA Type Approval #VCA/EMS/4567).
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets (Mercedes-Benz Group PT-1997).
Mercedes-Benz Technical Information System (TIS): Docs A16601, A16640, SIB 01.0187/98
VCA Type Approval Database (VCA/EMS/4567)
SAE International: DIN 70020 Engine Power Certification Standards
The Mercedes-Benz M 166.940 was used across Mercedes-Benz's W168/W202 platforms with transverse mounting in the W168 and longitudinal in the W202 and developed for compact and mid-size applications. This engine received platform-specific adaptations-reinforced mounts in the W168 and modified intake manifolds in the W202-and from 1999 the updated oil gallery system improved lubrication, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front timing cover (Mercedes-Benz TIS A16605). The 8th VIN digit indicates engine family ('M' for M166 series). Pre-1999 models have silver cam covers with ribbed valve covers; post-1999 units use black cam covers. Critical differentiation from standard M166: M 166.940 features specific intake manifold, red-painted valve covers, and unique ECU calibration. Service parts require production date verification - oil pumps for pre-1999 engines are incompatible with post-1999 revisions due to gallery redesign (Mercedes-Benz SIB 01.0187/98).
The M 166.940's primary reliability risk is camshaft wear on early builds, with elevated incidence in short-trip urban use. Internal Mercedes-Benz quality reports from 1999 noted a significant number of pre-1999 engines requiring camshaft replacement before 120,000 km, while UK DVSA records link a portion of high-idle instability to airflow meter drift. Cold-start cycles and extended idling increase valvetrain stress, making oil quality and interval adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1997-2001) and UK DVSA failure statistics (1998-2005). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M166940.
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.
