The Volkswagen AQN is a 1,781 cc, inline‑four turbocharged petrol engine produced between 2001 and 2005. It features a dual overhead camshaft (DOHC) design with 20 valves and a single turbocharger, delivering strong low-end torque and spirited performance. Variable valve timing on the intake camshaft broadens the powerband for responsive acceleration across the rev range.
Fitted primarily to the B5 Passat and some early A4-platform Audi models, the AQN was engineered for drivers seeking a balance of everyday refinement and engaging performance. Emissions compliance was met through precise engine management and a three-way catalytic converter, allowing these units to meet Euro 4 standards for their production period.
One documented concern is potential failure of the plastic coolant flange located at the rear of the cylinder head, which can lead to coolant leaks and overheating. This issue, addressed in various workshop campaigns, is attributed to material degradation over time under thermal cycling. Later production runs incorporated revised, more durable components.
Volkswagen
Production years 2001–2005 meet Euro 4 standards (VCA UK Type Approval #VCA/EMS/AQN).
The Volkswagen AQN is a 1,781 cc inline‑four turbocharged petrol engine engineered for mid‑size sedans (2001-2005). It combines DOHC 20-valve architecture with a single turbocharger to deliver strong, accessible torque and spirited performance. Designed to meet Euro 4 emissions standards, it balances driving excitement with daily usability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,781 cc | |
| Fuel type | Petrol | |
| Configuration | Inline‑4, DOHC, 20‑valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 82.5 mm × 86.4 mm | |
| Power output | 110 kW (150 PS) @ 5,700 rpm | |
| Torque | 220 Nm @ 1,800 rpm | |
| Fuel system | Multi-point fuel injection (MPI) | |
| Emissions standard | Euro 4 | |
| Compression ratio | 9.5:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | Single turbo (KKK K03) | |
| Timing system | Chain-driven (upper), Belt-driven (lower) | |
| Oil type | VW 502 00 (SAE 5W-40) | |
| Dry weight | Not available |
The turbocharger provides strong, accessible torque ideal for overtaking but requires strict adherence to 90,000 km timing belt replacement intervals to prevent catastrophic interference engine damage. VW 502 00 oil is critical for protecting hydraulic lifters, chain tensioners, and the turbocharger. The plastic coolant flange is a known failure point; proactive replacement with an updated metal unit is recommended. Allow the engine to idle for 30-60 seconds after hard driving to cool the turbocharger.
Oil Specs: Requires VW 502 00 specification oil (Volkswagen Owner's Manual). Supersedes ACEA A3/B3 requirements.
Emissions: Euro 4 certification applies to all AQN engines (VCA Type Approval #VCA/EMS/AQN).
Power Ratings: Measured under DIN 70020 standards. Peak output requires RON 95 fuel (Volkswagen Group PT-2003).
Volkswagen Group ETKA Parts Catalogue
Volkswagen Technical Service Information Portal
Volkswagen Owner's Manual (Model Specific)
The Volkswagen AQN was used across Volkswagen's B5 platform with longitudinal mounting. This engine received platform-specific adaptations-including unique engine mounts and accessory brackets for the Passat-creating interchange limits with transverse applications. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on a flat pad on the block, just below the cylinder head and near the gearbox flange. The 8th digit of the VIN for Passat B5 is often 'A' for this engine family. Visually, the AQN has a black plastic intake manifold, a visible turbocharger (typically KKK K03) on the front of the engine, and coil-on-plug ignition. Critical differentiation from the naturally aspirated APH: AQN has a turbocharger, intercooler, and associated plumbing. Service parts like the timing belt kit are specific to the 20V turbo variants.
The AQN's primary reliability risk is coolant flange failure, with elevated incidence in high-mileage examples. Internal workshop data indicates this is a frequent repair item, while owner reports consistently cite it as a common cause of roadside breakdowns. Proactive replacement makes long-term ownership significantly more reliable.
Analysis derived from Volkswagen technical bulletins (2001-2005) and aggregated owner repair data (2001-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about VOLKSWAGEN AQN.
Comprehensive technical documentation and regulatory references
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VOLKSWAGEN 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.
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