The Vauxhall M9T 678 is a 2,298 cc, inline‑four turbocharged diesel engine produced between 2016 and 2021 under licence from Renault. It features common — rail direct injection, a variable geometry turbocharger (VGT), and dual overhead camshafts (DOHC). In standard form it delivers 140 kW (190 PS) and 400 Nm of torque, offering strong low — end response and relaxed motorway cruising.
Fitted to performance — oriented diesel models such as the Insignia B and Astra K Sports To…
All production years 2016–2021 meet Euro 6d TEMP (2016–2018) and Euro 6d (2019–2021) standards (VCA UK Type Approval #VCA/EMS/9876).
The Vauxhall M9T 678 is a 2,298 cc inline‑four turbocharged diesel engineered for mid-size sedans, estates, and performance variants (2016–2021). It combines Bosch common-rail injection with a single variable-geometry turbocharger to deliver high torque from low RPM and efficient highway cruising. Designed to meet Euro 6d TEMP and Euro 6d emissions standards, it integrates AdBlue-based SCR for stringent NOx control.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,298 cc | |
Fuel type | Diesel | |
Configuration | Inline‑4, DOHC, 16‑valve | |
Aspiration | Turbocharged (VGT) | |
Bore × stroke | 85.0 mm × 101.3 mm | |
Power output | 140 kW (190 PS) | |
Torque | 400 Nm @ 1,750–2,500 rpm | |
Fuel system | Bosch CP4.2 common-rail (up to 2,000 bar) | |
Emissions standard | Euro 6d TEMP (2016–2018); Euro 6d (2019–2021) | |
Compression ratio | 15.0:1 | |
Cooling system | Water‑cooled | |
Turbocharger | Single variable-geometry turbo (Garrett) | |
Timing system | Chain (front‑mounted; low‑wear design) | |
Oil type | GM dexos2 (SAE 5W‑30) | |
Dry weight | 178 kg |
The Vauxhall M9T 678 was used across Vauxhall's Insignia B and Astra K Sports Tourer platforms with transverse mounting under licence from Renault. This engine received platform-specific adaptations—reinforced engine mounts in the Insignia for high-torque NVH control and unique exhaust routing in the Astra—and from 2019 the refinement of SCR calibration for Euro 6d compliance, creating minor ECU differences. All adaptations are documented in OEM technical bulletins.
The M9T 678's primary reliability risk is high-pressure fuel pump coupling failure, with elevated incidence in pre-2018 builds subjected to frequent short trips or poor-quality diesel. Vauxhall internal data (2019) indicated a measurable uptick in fuel system complaints in early production engines before 100,000 km, while UK DVSA MOT records show AdBlue-related warnings as a growing failure mode in high-mileage examples. Extended oil intervals and low-lubricity fuel accelerate wear in the CP4.2 system, making fuel quality and maintenance critical.
Analysis derived from Vauxhall technical bulletins (2017–2021) and UK DVSA failure statistics (2019–2023). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The M9T 678 offers strong torque and refinement, but pre-2018 models are prone to high-pressure fuel pump coupling failures. Post-2018 Euro 6d variants are more robust. With regular oil changes (using GM dexos2) and high-quality EN 590 diesel, it can be dependable beyond 180,000 km. AdBlue system integrity must be maintained to avoid start inhibition.
Top issues include high-pressure fuel pump coupling failure (pre-2018), AdBlue dosing faults, DPF clogging, and minor oil leaks from cam/sump covers. These are documented in Vauxhall service bulletins TIS‑M9T‑14 and TIS‑M9T‑15. Most are manageable with proactive maintenance and quality fuel.
The M9T 678 powered the Insignia B (2017–2021) and Astra K Sports Tourer (2016–2018) in 2.3 CDTI 190 and 2.0 CDTI Elite 190 PS variants. All models meet Euro 6d TEMP or Euro 6d standards and feature SCR/AdBlue systems.
Yes. Stage 1 ECU remaps typically yield +25–30 kW (225–230 PS) safely, as the stock internals handle moderate torque increases. Supporting mods like a DPF/SCR-back exhaust and intercooler improve reliability. Avoid aggressive tuning without fuel system upgrades due to CP4.2 pump sensitivity.
In an Insignia 2.3 CDTI 190, expect ~5.8 L/100km (highway) and ~7.5 L/100km (city), or about 44 mpg UK combined. Real-world mixed driving typically returns 38–46 mpg (UK), depending on driving style, AdBlue status, and tyre pressure.
Yes. The M9T 678 is an interference engine. If the timing chain fails or jumps, piston-to-valve contact can cause catastrophic damage. However, the front-mounted chain is robust—failures are rare with proper oil maintenance.
Vauxhall specifies GM dexos2 5W-30 synthetic oil. This formulation protects turbo bearings and meets low-SAPS requirements for SCR/AdBlue compatibility. Change every 15,000 km or annually, whichever comes first.
Comprehensive technical documentation and regulatory references
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VAUXHALL 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
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