Go LPG - Common used X300 faults
Used Jaguar X300's - Common faults.

Back Axle noise, especially on the over-run.

Don't be tempted to buy a car with any appreciable noise on the 'back end' You may have been told that the noise is due to a worn wheel bearing but this often not the case. Mostly, worn differential bearings are to blame.

Repair is expensive in both terms of parts and labour and there aren't many mechanics that can (or will) do the job. Finding a second-hand differential unit that is genuinely quiet is difficult, and the last thing you'd want is to spend a lot of money in having a used Diff. fitted only to find it is also noisy and the assurance that it is 'guaranteed' is worthless. The only way to buy a used unit is to stick to what you can test drive before buying and make sure that it is that unit you end up with. A new or reconditioned differential unit will set you back a long way, possibly costing half of what a car is 'worth', plus the labour of removal/refit.

Note that the labour element of this job is unpleasant to undertake, whilst seized bolts can hinder the job further. In my experience, the labour cost of removal and refit of a diff. unit is somewhere around £400 - £500, and that is without the supply/ repair of the diff. I have got 'lucky' in finding a used diff. unit that proved to be quiet but the total cost of buying it and having it fitted exceeded £800, not good if the car is 'worth' only £2000.

Alleged 'Spongy' Brake Pedal

The X300 braking system is quite different to that fitted to the XJ40. The XJ40 has a real 'drivers' pedal, moving very little before the brakes are being applied. The X300 (and XJ8 for that matter) have much more pedal travel before the brakes actually come into play.

I have heard XJ40 drivers make comments about 'Sponginess' of the X300 / XJ8 brake pedal and making an incorrect assumption that there is 'something wrong with the brakes' on X300's or XJ8's. I even had one MOT tester try to fail a car on 'no reserve footbrake travel' but soon educated him on these differences by inviting to speak to a Jaguar Agent and giving him the chance to try another car.

The plain fact is that the X300 / XJ8 has more pedal travel than XJ40's and some other makes. When someone claims to have found a 'brake fault' it is often due to them being unfamiliar with the model.

Digital Dashboard Clocks

I only see around 5% of cars with this clock actually working. There are replacements available from E Bay or similar, costing £35 - 70 plus fitting which can be DIY, although there is quite a lot of work involved removing trim etc. I have heard that the clock can be repaired by simply sliding in a piece of cardboard behind the PC board connection in order to tighten it up but I have not tried it to date.


I found the description of this repair kindly posted by someone on the excellent Jag Lovers website. Click this link - Jag Lovers - Dashboard Clock

Oil Pressure readings low or Zero and Oil light coming on

This is a common problem, especially on older or higher mileage cars. It can be alarming as it often denotes an engine which is about to expire on other makes. Worry not. I have had several cars that have shown zero Oil pressure, normally just after warm up. The X300 engine is 'bombproof' and I have never seen one quit in such circumstances. When checked out, it always has actual Oil pressure if checked with an in-line (mechanical) pressure gauge. The cause of the errant 'Zero' pressure indication is the electronic sensor which fails to work at certain temperatures when close to the end of its useful life. The cure is to fit a new or even a used sensor. This is a relatively easy thing to do although it is hard to get at.

Central Locking and Alarm Key Fob not Working

Key fob transmitters have a hard life and do wear out. It may be that new Fob Batteries (there are two, part number 2016) will bring the fob back to life. If that is the case then you are lucky. We often see fobs that have only one battery fitted by a previous owner and its not surprise that the fob does not work. Again, if that is the case with your fob you might get lucky, because....

A replacement fob costs around £120 plus VAT from Jaguar and then it must be adapted to the car. A secondhand one can be bought and adpated to suit the car if you can find one that works.

Cars that have 2 servicable fobs are rare, mainly because the first fob packed up and a previous owner moved on to using the second one. To be fair, getting one working fob with a car that has covered 100k miles is a bonus. Two working fobs is almost unheard of! If you haven't got a working fob at all and don't want to replace it, you don't have to buy one at all. The Alarm will be armed and disarmed by using the key to lock the doors. When opening the doors you have to get the key into the steering lock and switch on the ignition pretty quickly to stop the alarm horn sounding. See the Driver's handbook for more on this.

Boot opening (external) switch not working

The button used to open the X300 boot from outside the car operates a small switch. This can fail, although most often the wiring that crosses the boot hinge will have become stiff and broken through. It is not expensive to fix the problem but like many electrical jobs it can soak up a lot of expensive diagnostic time. It is always much cheaper to use the boot button inside the car, or the key from outside and leave well alone!

Heater not supplying hot air

In just about every case, this is due to the failure of the electric circulation pump, fitted on the NSF inner wing. Replacements are not cheap from Jaguar although a used one might be good. Specialists like David Manners can save you money on a new one.

NOTE! If your car is LPG converted a failed heater coolant pump can cause all sorts of problems because the LPG system relies on hot coolant being supplied by the heater circuit. If it doesn't get that, the LPG system will not perform properly.

Another cause of heater failure can be Air Locking, especially if the air is trapped in the heater matrix. This problem is much that same as Air Locking in a house radiator and has the same cure. There are various methods for 'bleeding' the air out. In extreme cases we've had to raise the front of the car whilst bleeding air out of the matrix.

If you bleed the heater matirix successfully only to suffer the same problem later on, start looking for a coolant leak before things progress to a more serious level.

Screen Washer Pump not working

Most often the pump itself will have failed. It is not easy to get at, requiring the removal of the OSF inner wing liner. Jaguar charge £47 inc. Vat for a new pump although note that many types of Ford screen wash pump can be made to fit. I have bought these at £2 each from a breaker. If you go down this route, take some of the wiring and the connecting plug along for the ride. Often these differ whilst the pump is similar mechanically.

Other causes can be simple blocking of washer nozzles and pipes or failure of the in-line non return valves.

There is a pictoral 'how to' item on Screen washer pumps on one of our other Jaguar pages - Jaguar faults

Rear Bumper Top Face Bright Trim.

These are often dented by careless folk dumping heavy items on top of the bumper before opening the boot. The top trim is not chromed steel as many expect, but high quality stainless steel. A new replacement trim costs £165 plus Vat from Jaguar. They are held on by all manner of awkward clips which break easily. Also be aware that the bumper has to be removed before replacement can commence, something which brings its own problems in terms of seized bolts and broken plastic.

Add the labour cost to the cost of the replacement trim and you could easily spend £300 total. If you are lucky and the dent is not serious, it is possible to remove the trim and carefully roll out the dent. For best results, ask an experienced panel beater to do this for you – NEVER use a hammer on the back of the trim without a sandbag on the other side or you'll end up with a worse dent in the other direction!

Rear Windows not working

This is another common X300 problem which is often due to simple lack of use. The motor is not too hard to remove and may respond well to freeing oil and TLC. You can plug the motor back in when it has been removed and check it for operation using the door switch (with ignition on) but mind your fingers!

Rear Shock Absorbers – Rattling noises on the back end………

This problem is often passed off or misdiagnosed as loose exhaust mountings, items moving in the boot or perhaps a loose rear bumper. If the noise occurs most often after going over a pot hole, it is more likely that the mounting bushes and bearings of the rear shock absorbers are to blame.

If the shocks themselves look old it is often a mistake to have them re-bushed. The only way to deal with this is to fit complete new shockers or have then fitted. The Jaguar replacement items are very expensive although David Manners supply a new pair (and I'd only recommend fitting a pair) for £127 delivered.

Don't be tempted to buy cheaper items as the top of the shocker shaft can snap right off during a good jolt, meaning the job must be done all over again. Removal and refit is, like the rear differential, not a fun job. Labour cost is around £150 a side (as long as none of the bolts shear off when being undone) making the total cost of a pair of rear shocks around £450.

I do not recommend DIY for this job. The good news is that the handling of a car with worn and noisy rear shock is dramatically transformed by fitting new ones!

Aerial Mast replacement

Often these are broken, damaged or simply seized. If seizure is the problem they do not normally retract or extend properly. The major cause of seizure is lack of regular cleaning of the mast by the previous owner or driver. As prescribed by Jaguar, the mast should be cleaned every 2 weeks or so using WD 40 and a soft cloth, wiping in an upward direction only. This stops the dirt from being pushed into the joints of the mast. If the mast has to be replaced beware that new ones are not cheap - £47 from Jaguar.

Air Conditioning not working.

By far the most common used X300 fault. The cause is often no more than a lack of use by the previous owner(s). As prescribed by Jaguar, the Air Con, should be turned on every 2 weeks or so to keep it maintained, Winter or Summer. The reason for this is simple once Air Con is understood;

Air Con. has many mechanical parts that require lubrication, bearings, seals and so on. The Air Con. system contains a gas that tends to remove ordinary mineral based oil or grease. To get around this problem a special lubricating oil formulation is added to the refrigerant gas. This oil only circulates to where it is needed when the Air Con. system is working. If this oil is not circulated, mechanical seizure can result.

Secondly, the many seals that keep the gas in the system will tend to dry out and shrink if they do not get a regular supply of this special oil. If the system isn't used regularly the seals will shrink and the gas will escape, leaving the system inoperative the next time it is called upon. As a result of this there is no special oil left in the system either. You will hear many people speak of a car's system needing a 're-gas' but this is often unsuccessful. Once those seals have shrunk to a certain level they will not come back to useful life and the gas just put in will leak out within a few days. A large repair bill then looms.

It is easy to spend £1000 or so on a Jaguar Air Con. System that has been neglected. On older cars it has to be judged as to whether it is worth doing this. If you are lucky enough to have Air Con. working in an X300 or any other car, look after it by running it every 2 weeks or so. It really is a case of 'Use it or lose it'.

Note that cars fitted with 'Climate control' only but having no Air Con, system are actually preferred by many – If Air Con. isn't fitted, it cannot break!

Cars that will not allow 'Drive' or Reverse to be selected from a start

If the brake light bulbs (or the circuit that feeds them) do not work, the gear selector interlock will not release from the 'Park' position when the brake pedal is pressed. It can take ages to select a gear in such a case. Also note that the Brake light switch itself can be faulty or out of adjustment, causing a similar problem although the bulbs are both good and the circuit is working.

Front and Rear Brake Discs - Warping and Wear

Wear is clear enough to diagnose. When the brake discs become too thin they need replacing. They are checked on MOT but sometimes a 'borderline' case will be let through the MOT, only to be well below par after a period of frequent use later on. Only replace them (or have them replaced) in pairs, 2 front or 2 rear, and with new pads. If you are DIY'ing, make sure the protective coating is cleaned off the discs before fitting the pads.

Disc Warping will manifest as 'pedal bounce' and may be felt through the steering, especially in the case of front discs. Replacement as prescribed above is the only realistic cure.

Petrol Cap drain blockage and Water Contamination of Fuel

Owners still using Petrol to run their cars get to see the petrol filler every day or two but those running on LPG rarely see it!

The filler drain hole and its filter are both prone to blockage by leaves and other debris, causing the filler to collect water. This is really undesirable. The water can leak into the Petrol tank under the submerged cap and cause you all manner of problems later on.

Check that your filler drain is clear. If it isn't, take out the filter and clean it. The drain pipe itself can be unblocked with a length of stiff wire. Test it out afterward with a little water and remember to keep an eye out for the next blockage (most likely in Autumn). For pic see our other page on Jaguar faults

Car Wash Damage to Paintwork

Easy to spot and often worse on top surfaces, roof, bonnet and boot lid. The laquer finish is 'fogged' (scratched) by the coarse nylon brushes. Often the damage cannot be polished out. Avoidance is easy - Never put your X 300 through a car wash!

Cars that Idle Eratically or Stall at Junctions

The first thing to check for is any air leakage after the air mass meter. The rubber 'Bellows' fitted to the inlet manifold is the main area to concentrate on. The second thing is much more subtle - Have you recently changed the spark plugs or had them changed?

X300's are notoriously sensitive to spark plug resistance. If this is incorrect, the ignition timing can oscillate between high advance and retard values, making the engine speed change dramatically. This makes the engine idle badly or stall. Some engines may not even start at all. If you find this just after changing the plugs, put the old ones back in until you have sorted out what is wrong with the new ones.

Replacing Oxygen (Lambda) Sensors

These are a consumable item and have a finite life. Testing or replacing them can be difficult. We came up with the X300 Lambda Connection Modification to make life easier.

Siezed Front Brake Calipers

A lot of X300 calipers sieze, we have replaced many. Dissasembly shows the cause to be split rubber piston seals which allow road water and salt in, resulting in corrosion. Almost without exception, the blame lies with the last but one person to change the pads, having used some unsuitable instruments and little care. The seal is damaged then, and in time corrosion takes its toll on the unprotected piston. Next time new pads are fitted, even by a careful person, the corroded portion of the piston is forced back into its cylinder and it will eventually sieze up.

Replacing the Fuel Filter

Take great care when undoing the union nuts to the filter - Often the fuel pipes are corroded and fall into a pile of dust. If that happens it's best to go back to good pipe both sides and splice new sections in, but it would be unwise to do this with worm drive clips and bits of fuel hose. Get same diameter push-on hydraulic or air connectors, they are an absolute doddle to fit and no risk of leaks as they are designed for far higher pressures than present in Jaguar fuel delivery. Best to check that the parst you are buying will be fuel proof! For the missing pipe you can use new plastic fuel pipe. At the filter end(s) things might be easy or complicated, depends on the conditions of the union nuts. If they are scrap then you could replace them or go for a filter with different connections that can be bought to match.

Replacing the Throttle Position Sensor (TPS)

The TPS is driven (rotated) by a tang much like the end of a standard screwdriver. Because of that it can be wrongly installed, 180 degrees out.

I have seen one that read over 4.5V at idle, the result of the fitter rotating it before putting the bolts in. To ensure correct installation you should see around 0.5V or less than 10% on a scanner at idle. If you don't have a scanner you can check the voltage on the green wire with yellow bands (TPS signal wire to ECU) using a multimeter. The engine does not have to be running to do this check (it is better that it isn't!), just have the ignition on, look for 0.5V at idle position and around 4.5V full throttle.

Just to finish this off, one should not expect to see 0V at idle (that shows that the circuit is dead) nor 5V at full chat. Those clever backroom boys left margins at both ends (a) to show the ciruit is live and functioning as described above, and (b) for the avoidance of increasing (over time, with age and corrosion)) resistance potentially messing up idle values. It is a lesson that Ford learned a while ago and carried over.

Engine Cranking - No Start.

During cranking, observe the tachometer - It should show around 200 RPM. If if doesn't, the Crank Position Sensor (CPS) is likely to be at fault. This test has been demonstrated not to be definitive though, the sensor may still be bad even if the tacho. shows cranking RPM. The sensor is easy to get at, being mounted close to the front Crankshaft pulley on the fornt of the engine. The worst you will encounter are siezed mounting bolts. If the sensor has done more than 50K miles or so, replace it anyhow - They do not last forever and will catch you out one day.

The X300 Crank Sensor

Rough Running after Plug or Coil Changes

If the coil wires for cylinders 5 and 6 on an AJ16 are mixed up (easily done) your previously smooth running pride and joy can be turned into something akin to a bag of spanners. I've seen one of the cat.s glowing red hot on a car bought here for diagnosis as the fuel was not being burned in either cylinder, but it was in the cat. The wiring for coil 6 often had a ring of yellow tape around it (even Jaguar suffered this problem) but with age the tape can fall right off, it is then very easy to mix the two. It's really good practice to replace it (whether the tape is present or not) with a tiny cable tie which should last the life of the car.

Wiring for Coils 5 and 6 are easily mixed up, The Yellow tape show which is meant for 6.

The Yellow tape marks the wiring for Cylinder / Coil 6.

Noisy Fuel Pump? Is it about to fail?

The pump may indeed be about to fail, but let me put a slightly different slant on it;

If the pump were struggling to supply fuel due to some kind of restriction (say a blocked fuel filter), then you'd expect it to be noisier in operation because of the increased load placed upon it. You might then expect it to fail as a result of that increased load.

It might be prudent to check the entire fuel delivery/return system for restriction before diving in to fit a new pump which, after all, is as likely to be noisy if there are other problems.

X300 Gearbox Warning Lamp

There are few things on an X300 that cause more confusion and misunderstanding than this one.

The most common reason for this lamp to be illuminated has nothing to do with the Gearbox at all.

The warning is often generated by an engine stall. It simply means that the engine management system knows that something does not add up (and it wouldn't if the engine isn't running!). The illumination of this lamp merely indicates that the gearbox has been limited in is operation. It does NOT mean that the gearbox fluid is low, nor does it mean that the gearbox is malfunctioning or has suffered any damage.

If the lamp has been illuminated as the result of an engine stall, it will clear (turn off) if the engine is stopped for a minute or so, then restarted. Normal service will then be resumed, at least until the next engine stall. You'll need to progress by focussing on why the engine is stalling, not by worrying if there is anything wrong with the gearbox.

X300 Poor Idle Quality - Exhaust Valves Sticking Partially Open

This phenomenon was well known to Jaguar, but not their fault. The use the vehicle was put to was a major factor, along with fuel quality.

Click HERE to read a page from the service bulletin.

X300 Engine Timing

This isn't needed very often, but mostly after head removal as the cars get older. There wasn't much clear advice on the 'net when I wanted it so here are the basic facts;


Engine Immobiliser

To check if the engine is immobilised by the chip-in-key system;

Begin with the key removed for around 2 mins or more.
Put the key in and rotate to the Ignition position, but do not crank the engine or move the key to that position.
You should get a full set of warning lights as shown in the picture below;

After 30 sec.s or so, all of those warning lights, EXCEPT the Check Engine Light (CEL) should extinguish.

The CEL should remain lit as in the picture below;

If the CEL is extinguished before cranking, the engine has been immobilised.

X300 Boot Lock Mechanism Access

To get the Boot (Trunk) lid open when all other methods fail, remove the rear number or licence plate and cut a hole in this location. The boot can be easily opened now and in the future. A hole saw is great for the job.

The lock mechanism can be easiy operated by working out which rod comes from the outside lock, and then pulling it with fingers or pliers.

When finished, the hole can be covered with heavy tape and once the numberplate is re-fitted the hole will be invisible.

With more time, the best method would be to find a suitable size body Grommet and cut the hole to suit it. The edge of the hole should be painted or at least greased to prevent corrosion.

It may not be necessary to bore a hole this large into your Boot lid just to get it open, the example picture shows a large hole primarliy chosen to show you the mechanism inside. With good aim you may well get away with a smaller hole, but remember that if using a hole saw, you only get one chance as the centre is then gone.

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