2004 Jaguar XJ Problems: 11 Known Issues

On the 2004-2009 Jaguar XJ, an NVH pad fitted to the underfloor undertray of early X350 XJ sedans traps road salt and moisture against the steel brake pipes running under the floor and over the rear crossmember. The pipes corrode from the outside in and eventually lose mechanical integrity. Because the X350 uses a diagonally split dual circuit, a single pipe failure gives long pedal travel and reduced braking in one circuit; if both circuits lose integrity, service braking is lost entirely. Jaguar issued a voluntary safety recall covering 14,493 US vehicles built at Brown's Lane between 2 January 2003 and 19 January 2004. This is a corrosion-driven failure that keeps appearing on unrepaired salt-belt cars long after the recall window, and on later X350/X358 cars that were never in scope.

On the 2004-2009 Jaguar XJ, the X350/X358 replaced the mechanical handbrake with an electric park brake driven by a module mounted in the boot, behind the right-hand trim panel ahead of the wheel arch. Two failure paths dominate. The module itself is in a location that sees moisture from the well-documented boot water leaks on this car, and it corrodes. Separately, the system requires a service-mode retract and a recalibration whenever the rear calipers are opened; a rear pad job done without that procedure leaves the actuators out of position and sets a permanent fault. The failure mode owners fear most is the brake seizing applied, which immobilises the car — it cannot be released by pulling a lever, because there isn't one.

On the 2004-2009 Jaguar XJ, the naturally aspirated and supercharged 4.2-litre AJ34 V8 in the X350/X358 carries an unusually large amount of load-bearing plastic in the cooling system. The thermostat housing is plastic and its internal support fractures, which lets coolant recirculate through the engine while bypassing the radiator — the car overheats even though the coolant level and the pump are fine, which sends people chasing head gaskets. Separately, the water pump uses a composite impeller that erodes and shreds, and the plastic retaining ring holding the pump's O-ring crumbles at the bottom of the pump. Additional chronic weep points are the overflow nipple on the coolant expansion tank and the two heater hoses that run beneath the intake manifold. This is a distinct problem from the X351's water pump failures — different engine family, different parts.

On the 2004-2009 Jaguar XJ, this page previously presented one 2004-2009 electronic-throttle-body failure pattern as established fact. The audited official material does not verify that broad cause or model-year scope. It does show a direct safety conflict: NHTSA manufacturer-communication record 10017595 identifies Jaguar bulletin XJ303-10 for the 2004 XJ as “Electronic Throttle Body - Cleaning Prohibited.” Treat throttle symptoms as a reason for model-year-specific diagnosis, not proof that the throttle body needs cleaning or replacement.

On the 2004-2009 Jaguar XJ, the rear crankshaft main seal on AJ-V8 engines in the XJ develops a slow oil leak over time. The leak worsens as the seal hardens and the crankshaft seal surface develops minor wear grooves. Oil drips onto the transmission bellhousing.

On the 2004-2009 Jaguar XJ, x350/X358 cars leak water into the cabin and boot by two separate and frequently confused routes. In the boot, water runs down the boot aperture and gets behind the black plastic strips at each rear lamp cluster; the rear vent seals behind the rear bumper below the lamps also fail. The boot floor then pools water, soaking the carpet and, critically, the modules Jaguar located back there — the electronic park brake module and the rear electronics. Separately, the sunroof drains run down the A-pillars and clog with pollen and debris; when they block, water backs up into the headliner and drops into the front footwells onto more electronics. Both routes explain a large share of this car's reputation for unexplained electrical faults: the electrical symptom is downstream of a water problem.

On the 2004-2009 Jaguar XJ, the 2004-2009 X350/X358 XJ was Jaguar's first all-aluminium monocoque, yet it is notoriously prone to paint blistering. Steel particles from the panel presses trapped in the aluminium sheet before painting, plus galvanic action where dissimilar-metal fixings and trapped salt water meet the aluminium, cause filiform (worm-like) corrosion under the paint. Owners report it first on the leading edge of the boot lid near the rear screen, then door bottoms, wheel-arch lips, bonnet edges and the A/B/C pillars. Jaguar's corrosion warranty (6 years UK, 10 years US) covered some cars, but many owners were refused once out of warranty even though the blistering clearly started earlier. It is cosmetic rather than structural, but it is expensive to repair correctly because aluminium panels must be stripped back, treated and repainted.

On the 2004-2012 Jaguar XJ, the XJ suffers from cascading electrical faults caused by body control module (BCM) software glitches and CAN bus communication errors. Phantom warning lights, inoperative features, and intermittent failures across multiple systems are common, especially after battery disconnection or jump-starting.

On the 2004-2009 Jaguar XJ, the 2004-2009 X350/X358 uses a saddle-shaped fuel tank straddling the driveshaft, with a lift pump on one side and a venturi jet pump transferring fuel from the other. When the jet pump or the lift pump module degrades, the engine side of the tank runs dry even though the gauge shows fuel: owners report momentary stutters or stalls at highway speed, hard starts in cold weather, and gauges that drop suddenly or read unreliably because the level senders are built into the non-serviceable pump modules. It affects the V8 and V6 petrol cars and the 2.7 diesel. The pump module is a sealed unit so the sender is replaced with the pump.

On the 2004-2009 Jaguar XJ, the X350/X358 uses aluminium front lower control arms with pressed-in rubber bushings that were not originally available as a separate service part. The rubber delaminates from its inner sleeve and the arm develops fore-aft play, producing a clunk over bumps and when the suspension is loaded in corners. Because the aluminium body and double-wishbone front end are otherwise well regarded, owners often misdiagnose the noise as a ball joint, a sway bar link, or — expensively — as an air suspension fault. Untreated, the play walks the front alignment out and eats front tyres on the inner edge. Owners commonly report the bushings gone by 65,000-100,000 miles, well ahead of the ball joints in the same arm.

On the 2004-2009 Jaguar XJ, the X350's ZF 6HP26 six-speed automatic passes its transmission control module wiring through a plastic connector sleeve in the side of the case, and uses a plastic oil pan with an integrated filter. Both parts are heat-cycled by transmission fluid for their whole service life and both eventually harden and leak — the sleeve at its seal, the pan at the gasket face or through fatigue cracks. The leak is deceptive: with the car parked, fluid level sits below the sleeve, so nothing drips until fluid migrates back to the sump over several days, which is why owners chase phantom drips. Jaguar's original 'sealed for life, no dipstick' fluid policy means most cars reach this point on original fluid, which compounds the problem with harsh or delayed shifting. Fluid wicking up the sleeve into the loom can also reach the TCM connector and produce electrical shift faults.