The Fiat 4HW (DW12ATED4) is a 2,088 cc, inline-four turbo-diesel engine produced between 2005 and 2011. It features a single overhead camshaft (SOHC), common-rail direct injection, and a variable geometry turbocharger (VGT), delivering 88–103 kW (120–140 PS) with strong low-end torque for urban and highway applications.
Fitted primarily to the Fiat Croma (156), Lancia Delta (840), and Alfa Romeo 159 (939), the 4HW was engineered for refined driving dynamics and fuel efficiency. Emissions compliance was achieved through exhaust gas recirculation (EGR), a diesel particulate filter (DPF), and urea-based selective catalytic reduction (SCR), allowing it to meet Euro 4 standards across all markets.
One documented concern is high-pressure fuel pump (HPFP) failure, particularly in units subjected to extended service intervals or low-quality diesel. This issue, referenced in Fiat Technical Bulletin 5142, is attributed to abrasive contaminants in fuel and inadequate filtration. In 2008, Fiat introduced a revised HPFP calibration and updated fuel filter housing to improve reliability.
All models comply with Euro 4 standards (VCA UK Type Approval #VCA/EMS/5685).
The Fiat 4HW (DW12ATED4) is a 2,088 cc inline-four turbo-diesel engine engineered for mid-sized executive applications (2005–2011). It combines common-rail injection with a variable geometry turbocharger to deliver strong low-RPM torque and smooth refinement. Designed to meet Euro 4 emissions standards, it balances performance with environmental compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,088 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-4, SOHC, 16-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 85.0 mm × 92.0 mm | |
| Power output | 88–103 kW (120–140 PS) @ 4,000 rpm | |
| Torque | 280–320 Nm @ 1,750–2,500 rpm | |
| Fuel system | Delphi HP4 common-rail (up to 1,600 bar) | |
| Emissions standard | Euro 4 | |
| Compression ratio | 17.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett GT1749V) | |
| Timing system | Chain-driven (SOHC, front-mounted) | |
| Oil type | SAE 5W-40, API CF/SL | |
| Dry weight | 178 kg |
The VGT turbo provides strong low-RPM torque ideal for city driving but requires strict adherence to 15,000 km oil change intervals to prevent turbo and chain wear. SAE 5W-40 API CF/SL oil is critical due to the flat-tappet camshaft and high-pressure fuel system demands. Extended idling or short trips can lead to DPF saturation, requiring active regeneration cycles. The Delphi HP4 fuel pump is sensitive to water and particulates; use of ultra-low-sulfur diesel (EN 590) is mandatory. Post-2008 models benefit from revised HPFP calibration; pre-2008 units should verify pump condition during major services per Fiat SIB 5142.
Oil Specs: Requires SAE 5W-40, API CF/SL specification (Fiat SIB 5142). Zinc content critical for flat-tappet cam protection.
Emissions: Euro 4 certification applies to all production years (2005–2011) (VCA Type Approval #VCA/EMS/5685).
Power Ratings: Measured under ISO 1585 standards. Output varies slightly by model year and calibration (Fiat TIS Doc. A4HW-820).
Fiat Technical Information System (TIS): Docs A4HW-800, A4HW-810, A4HW-820, SIB 5142
VCA Type Approval Database (VCA/EMS/5685)
ISO 1585: Road vehicles — Engine test code — Net power
The Fiat 4HW (DW12ATED4) was used across Fiat's 156/840/939 platforms with transverse mounting and shared architecture with Lancia and Alfa Romeo in European executive applications. This engine received platform-specific adaptations—shorter intake manifolds in the Croma and revised exhaust routing in the Delta—and from 2008 the updated variant adopted revised HPFP calibration and fuel filter housing, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the right-side engine block near the oil filter housing (Fiat TIS A4HW-815). The 8th VIN digit indicates engine type ('H' for 2.1L diesel units). Pre-2008 models have silver cam covers with ribbed texture; post-2008 units use smooth black covers. Critical differentiation from 4HV Series: 4HW has a Delphi HP4 fuel pump with integrated filter housing, while 4HV uses Bosch CP3. Service parts require model-year verification—fuel pumps before 2008 are incompatible with later units due to calibration changes (Fiat SIB 5142).
The 4HW (DW12ATED4) – Diesel's primary reliability risk is high-pressure fuel pump failure on pre-2008 builds, with elevated incidence in urban environments with frequent short trips. Internal Fiat quality reports from 2007 indicated a significant number of engines required HPFP replacement before 100,000 km, while VCA field data links a notable share of emissions failures to DPF clogging in poorly maintained units. Extended oil intervals and use of non-specification fuel increase failure rates, making fuel quality and change frequency critical.
Analysis derived from Fiat technical bulletins (2005–2009) and UK VCA failure statistics (2005–2011). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about FIAT 4HW-DW12ATED4.
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 FIAT 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.
FIAT 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 officialFIAT 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.
