XJ X350

Jaguar have always been an innovative company but have started to create very complex vehicles since the turn of the millennium, virtually pioneering modern aluminium construction techniques with the launch of the X350 XJ model. This modern take on the classic Jag uses fibre optic cables for its data transmission systems and is fitted with a dynamic air suspension setup. Because of this, the X350 and facelifted X358 XJ require specialist diagnostic equipment to trace certain problems and require an even higher level of caution than normal just to lift them off the ground.

With over 100 years’ experience working on JLR vehicles, our access to SDD and the TOPIx system, K Motors are uniquely qualified to provide technical support, to troubleshoot and to find and fix any faults on the XJ.

This is a list of some of the more common faults found on the X350 and X358 XJ with solutions on how to fix them.

As with other vehicles using this engine, the X350/X358 can suffer from crankshaft failure, this engine can unfortunately spin its mainshaft bearings, starving the engine of oil and the crankshaft can actually snap!

Because of the extensive damage caused by crankshaft failure, a replacement engine will need to be sourced from Jaguar.

The XJ has a double wishbone suspension setup affording it terrific handling capabilities for such a large car, unfortunately this makes it pretty hard on suspension bushes, coupling that with the fact that rose joints are used on some of the wishbone bushes means that the control arms on the XJ can have a life expectancy of around 5 years.

You may notice a nervousness to the handling especially over bumps, or a knocking noise on rougher roads, but because the XJ is so well insulated from noise, you may not notice they have failed until the MOT tester informs you. Apart from the front air struts needing to be removed to get the upper wishbones out, all 4 arms are pretty straightforward to replace. We strongly recommend a 4-wheel alignment after installation because changing control arms tends to alter the geometry of the vehicle.

By far the most common issue with the air suspension on the X350 XJ is a fault with the air compressor itself. The symptoms are the “Air Suspension Fault” message and an amber warning light. Plugging an XJ afflicted with these problems will likely bring up the infamous C2302 – levelling plausibility and/or C2303 – Reservoir plausibility errors. These basically mean that the suspension is not getting air quick enough to rise to the correct level and fill the reservoir in the boot. This is generally caused by the Teflon ring around the piston wearing thin and not creating a proper seal as it goes up and down, forcing it to work harder to get the suspension to the correct height and top the reservoir up. This can eventually cause the compressor to wear out.

There are two options for repair, either replace the compressor assembly behind the left-hand wheel arch liner or pull it out and replace the Teflon piston ring, likely, this will be all that is required. It is essential to replace the relay when repairing or replacing a faulty compressor as it will have faced excess on/off cycles having to keep switching the compressor on so often generating a lot of heat.

The height sensors are rarely the issue with the air suspension on the Jaguar XJ, but if you find that the ride height is incorrect on one corner, that sensor may need to come off for cleaning or replacement and the system may require calibration. Note that 2003 models had 4 height sensors (one for each wheel) whereas newer models make do without the sensor on the front right-hand side.

The valve block is a control solenoid fitted to the air reservoir in the boot which is fed from the compressor, the valve block has a port for each air spring and releases controlled bursts of pressurised air from the reservoir to inflate them. Over time the valves used in these ports can get sticky or blocked with contaminants, this can cause similar symptoms to a failed air spring so should not be overlooked in the diagnostic process.

Replacement involves discharging the system and recalibration but is straightforward due to its location in the boot.

Whilst Brembo brakes are a desired feature on most vehicles, they can cause problems on R model Jags, the front calipers can sometimes stick on slightly making the brake pads very hot and resulting in either brake fade and/or warped discs which causes a wobbling steering wheel when moving or braking.

The fix is new discs, pads and a brake caliper rebuild where the seals are replaced and the pistons are cleaned or replaced. When changing the brake discs at the front a DTI gauge must be used in order to mount the discs as square as possible on the hub.

The main cause of problems with the Brembo brake system on these cars is pad knock-back. Brake pad knock-back or brake knock off is a phenomenon that occurs mostly in motorsport where movement of the brake disc pushes the brake pads away from the centreline of the discs rotation, meaning there is a large gap between the pads and discs when the pedal is pushed. This is seen regularly on early X350 XJR models and is the main reason Jaguar swapped over to the ATE floating caliper setup as quickly as they did.

Pad knock-back can cause the brake pedal to feel spongey or soft and because of the void between the pads and discs, can make it feel as though the brakes are not doing anything when the pedal is applied until you take your foot off the brakes and apply them again.

To minimize knock-back it is important to keep on top of brake pad and discs changes and to monitor the condition of the Brembo calipers ensuring that the aluminium pistons are not seized.