First — which 2003 XJ are you looking at?
This matters before anything else, because a 2003 XJ Vanden Plas can be one of two very different cars. Most 2003 examples sold in North America are the outgoing steel-bodied model (the X308) with a 4.0-litre V8 and a five-speed automatic on conventional springs. The all-new aluminium model (the X350) — 4.2-litre V8, six-speed automatic, and air suspension at all four corners — arrived as a 2004 model, though the earliest cars were built in 2003. The quickest way to tell them apart is the engine: a 4.0-litre is the older X308, a 4.2-litre is the aluminium X350. The rest of this page covers the aluminium X350. If yours is the 4.0 X308, the big-ticket items are different — most notably that earlier V8's plastic timing-chain tensioners — so confirm the car by its engine and VIN first.
Why it can be a good car
When the X350 launched in 2003, Jaguar built an aluminium monocoque luxury sedan that weighed hundreds of pounds less than its predecessor, rode on air suspension at all four corners, and used a fibre-optic data network between its modules. Under the hood is the AJ 4.2-litre V8, thoroughly sorted by this point, mated to the robust ZF six-speed automatic that shares architecture with BMW and Range Rover applications. The aluminium body cannot rust in the conventional sense, and the long-wheelbase Vanden Plas has one of the most comfortable rear cabins ever fitted to a sedan at this price. Well-kept examples go past 200,000 miles.
Why it can be a bad car
The engine is one of the strongest parts of the package — the cost of this car has very little to do with it and almost everything to do with what surrounds it. The air suspension, the A/C, and the proprietary electrical network are where the money goes, and on a neglected example those bills stack up fast. Buy the right one and it is a magnificent car for the money; buy the wrong one and it will test your patience and your wallet.
Does it have a timing belt or a timing chain?
A timing chain. The AJ 4.2 V8 uses chains with metal tensioners — the design that resolved the plastic-tensioner failures of the earlier generation — so there is no timing belt to replace.
The things to check before you buy
- Air suspension The defining X350 issue, with failures common past roughly 100,000 miles. The car should sit dead level, still sit level the next morning after being parked overnight, and the compressor should run briefly at startup and stop — not cycle continuously.
- Air conditioning Confirm it actually blows cold and that the compressor clutch engages; a dead compressor costs far more than a recharge.
- Transmission service The ZF "lifetime" fluid is not actually lifetime. On a neglected unit at high mileage this gets very expensive, so look for a record of a fluid service.
- Front control-arm bushings On the X350, Jaguar's own catalogue often supplies these as part of a complete control-arm assembly, which makes them a pricier fix than a bushing alone (separate aftermarket bushings do exist). Listen for knocks over bumps and during slow turns.
- Electrical system The X350 uses a Jaguar-proprietary diagnostic system — a generic code reader will not see every module. Any persistent dash warning needs a proper Jaguar-capable scan.
What would make you walk (or hard-negotiate)
- Air suspension trouble Any corner sagging overnight, the compressor cycling continuously, or an "Air Suspension Fault" message — full-system wear is documented at this age.
- Transmission fault Any "transmission fault" message, harsh shifts, or shudder, especially with no service record.
- Front-end knock Knocking or grinding from the front during slow turns points to worn control-arm bushings — an expensive job because of how Jaguar sells the part.