The Citroen UKZ (ZPJ4/Z) is a 1,998 cc, inline-four petrol engine produced between 1998 and 2004. It forms part of the PSA ZJ engine family, featuring a dual overhead camshaft (DOHC), 16-valve configuration, and multi-point fuel injection (MPFI). In standard tune, it delivers 89 kW (121 PS), providing balanced performance for mid-size platforms such as the Xantia and 406.
Fitted to models such as the Xantia Exclusive and 406 Coupe, the UKZ (ZPJ4/Z) was engineered for refined, highway-oriented driving with smooth power delivery and low NVH. Emissions compliance was achieved through a three-way catalytic converter, meeting Euro 3 standards throughout its production run. The engine features hydraulic tappets and a timing belt, designed for ease of maintenance and long-term durability.
One documented concern is cylinder head cracking around the exhaust ports, particularly in early production units, highlighted in PSA Technical Service Bulletin TSB-ENG-0213. This issue is typically linked to prolonged overheating or inadequate coolant maintenance. Later production revisions incorporated improved cylinder head casting techniques to reduce thermal stress concentration.
Production years 1998–2004 meet Euro 3 standards (VCA UK Type Approval #VCA/EMS/3456).
The Citroen UKZ (ZPJ4/Z) is a 1,998 cc inline-four petrol engine engineered for mid-size platforms (1998–2004). It combines multi-point fuel injection with a dual overhead camshaft to deliver responsive mid-range performance. Designed to meet Euro 3 standards, it balances drivability with durability for everyday ownership.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.6 mm | |
| Power output | 89 kW (121 PS) @ 5,500 rpm | |
| Torque | 178 Nm @ 3,750 rpm | |
| Fuel system | Multi-point fuel injection (MPFI) | |
| Emissions standard | Euro 3 | |
| Compression ratio | 10.2:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Timing belt (interval: 120,000 km or 6 years) | |
| Oil type | SAE 10W-40 (ACEA A2) | |
| Dry weight | 132 kg |
The naturally aspirated DOHC design provides linear power delivery ideal for highway cruising but requires strict adherence to 120,000 km or 6-year timing belt replacement intervals to prevent valve damage. SAE 10W-40 oil meeting ACEA A2 is essential for valvetrain longevity. Extended high-speed operation without cooling system maintenance may accelerate head gasket or exhaust port cracking. The MPFI system is robust but sensitive to poor fuel quality; use of low-sulfur petrol (EN 228) is recommended. Pre-2001 units should have cylinder head integrity inspected per PSA TSB-ENG-0213.
Oil Specs: Requires SAE 10W-40 meeting ACEA A2 specification (PSA SIB 02 13 01). Compatible with API SL in non-turbo applications.
Emissions: Euro 3 certification applies to all models (1998–2004) (VCA Type Approval #VCA/EMS/3456).
Power Ratings: Measured under ISO 1585 standards. Output consistent across fuel grades meeting EN 228.
PSA Technical Information System (TIS): Docs ZPJ4Z-001, ZPJ4Z-002, ZPJ4Z-003, TSB-ENG-0213
VCA Type Approval Database (VCA/EMS/3456)
ISO International: ISO 1585 Road vehicles — Passenger cars — Test code for determination of net power
The Citroen UKZ (ZPJ4/Z) was used across Citroen's Xantia/406 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced mounts in the 406 Coupe and revised intake manifolds in the Xantia Exclusive-and from 2001 the facelifted Xantia models adopted updated engine management software, creating minor calibration differences. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the left-side cylinder block near the exhaust manifold (PSA TIS ZJ-1998). The 8th VIN digit indicates engine type ('G' for ZPJ4/Z). Pre-2001 models have red valve covers; post-2001 units use black valve covers. Critical differentiation from XU10: UKZ (ZPJ4/Z) uses a 1,998 cc displacement with 87.0 mm bore, while XU10 has 1,905 cc and 86.0 mm bore. Service parts require production date verification - timing belts for pre-2001 models are incompatible with later revisions due to pulley redesign (PSA SIB 03 04 12).
The UKZ (ZPJ4/Z)'s primary reliability risk is cylinder head cracking on early builds, with elevated incidence in high-load operation with delayed coolant changes. Internal PSA quality reports from 2002 indicated a notable number of pre-2001 engines requiring head replacement before 150,000 km, while UK DVSA records show timing belt neglect as a leading cause of engine seizure. Prolonged motorway driving and coolant degradation increase thermal stress, making cooling system maintenance critical.
Analysis derived from PSA technical bulletins (1998-2004) and UK DVSA failure statistics (2000-2010). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about CITROEN UKZ-ZPJ4Z.
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 CITROEN 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.
CITROEN 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 officialCITROEN 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.
