2006 XK8....

This morning I noticed that the passenger headrest was fully extended. I was puzzled because my wife always keeps both headrests in the fully-lowered position. I lowered the passenger headrest using the lever on the side of the seat. It lowered properly, but as soon as it did and I released the lever, it slowly rose to full extension all on its on. So I lowered it again, and when i released the lever, up it went all on its own again....

I glanced at the drivers headrest and noticed that it was raised just over an inch. I walked to the drivers side of the car, used the lever to lower the drivers headrest, and as soon as I released the lever, it slowly rose to just over an inch high again. So I lowered it again, and when I released the lever, up it went to just over an inch high again....

Last weekend, it was the airbag system throwing a false code 17. This weekend, it's the haunted headrests. Anyone have any idea why these headrests are moving all by themselves? All I want to do is put them both in the fully-lowered position and keep them there permanently....

 

Have you tried to re-memorize the desired headrest (and seat) position?

 

No, I have not....

But what apparently worked was using the headrest controls on the bottom side of each seat. When my wife used them to lower the headrests just now instead of using the lever on the top side of each seat as I did, her headrests both went down and stayed down. I was not aware of the headrest controls on the bottom side of each seat. Now I am. But that still does not explain how these headrests moved all on their own without input from either of the two headrest control switches for each seat....

Yet another electrical quirk, I suppose. This car is full of 'em....

 

Aha--I had to read through your post twice to figure this one out. The lever at the top of the seat is NOT a headrest adjustment. Lifting that lever is for slanting the seatback forward to have access to the rear. It also serves to temporarily lower the headrest so that it does not scrape against the headliner when moving the seatback. Absolutely normal operation.

As you found out the switch at the BASE of each seat is the one that adjusts the headrests.

Doug

 

But that still does not explain how both headrests originally raised themselves without anyone activating the switches on the base of either seat....

The car is haunted, I tell you....

 

Nothing to explain here. This is more or less normal operation for these vehicles. My memory function has frequently worked incorrectly with seats and seatbacks moving into positions that I had never set. Goes in the same category and random warning messages that come on for no reason and then go off again, etc. I guess it is the ghost of Lucas.


Doug

 

Doug,

Nice try, but Halloween is coming it must be a ghost!

 

The Lever on The Side of the seat lets you move the seat back foward when this is done the headrest lowers when pulled back the headrest resumes it last possion.

 

The poltergeist could be in the Seat Back Tilt/Headrest adjustor:



This is my driver's seat viewed from behind with the seat back tilted forwards. UK RHD so it's the opposite way round to yours.

The microswitch circled in red controls the headrest retract / reset. As the seat back is tilted for access to the rear seat, the headrest fully retracts. When the seat back is returned to the normal position, the headrest returns to its preset height.

This headrest movement can be triggered by pressing the microswitch blade. If you have a harness fault to the switch or it needs cleaning, this could be the cause.

Graham

 

Thanks for the additional information, Graham. If this situation reoccurs, I'll attempt to clean the microswitches and harnesses. Thus far, both headrests have stayed completely lowered since Saturday morning....

 

My wife reported more evidence of this car's electronics systems being haunted today:

While she was driving about 50 mph in a long sweeping curve, two messages appeared on the dash. "Cruise not available" and "Check rear lights". After coming out of the curve, she tried to engage cruise control, and it would indeed not work. So she pulled over, shut the ignition off, waited a minute or two, cranked the ignition, and resumed her trip. No more messages, but cruise control still would not function. She arrived at her meeting, parked, shut the car off, locked it, and went inside. After her meeting ended a couple of hours later, she returned to her car, cranked the ignition, and left. No more messages, and now the cruise control functioned perfectly....

I installed a new Bosch 49-850B vented battery just one month ago due to random DSC and ABS messages along with the trunk popping open all by itself a couple of times. Those issues stopped after the new battery was in place....

Two weekends ago, she had the false airbag code 17. Last weekend, it was the haunted headrests that moved all by themselves. Not to mention the worn-out plastic intake tube that I discovered and had to replace....

Now this new issue all of the sudden. Are there yaw and pitch sensors that may be throwing false codes? Or should I just check the battery ground for solid contact?

Any assistance or recommendations would be greatly appreciated. This XK8 is eating up far too much of my time. I am beginning to truly dislike this car....

 

Jon,

I'm also less than impressed with anything to do with DSC on the 4.2 vehicles. It may have looked wonderful in a CAD drawing at the Browns Lane factory but is nowhere near sufficiently robust or reliable in practice.

If it's any consolation whatsoever, I've had similar amber warnings which disappear when the vehicle is next used. These don't set DTC's and the only way I can think to troubleshoot them is to drive around with AutoEnginuity permanently connected and recording on each trip!

The 'Check Rear Lights' is not one I've had. According to the handbook, it indicates a blown bulb. Logically it shouldn't therefore go out until the faulty bulb is replaced. Of course, if you don't have a bulb blown in the first place, it's yet another example of over sensitive sensoring.

Graham

 

Thanks for your feedback, Graham. I wonder what additional false messages this car will decide to throw this weekend. I'm sick of messing with it....

 

In the five page list of Warning Messages in the Driver's Handbook, there's one I'm eagerly waiting to appear. It's a red warning:

DRIVER INTERVENE

The handbook usefully explains the meaning as 'driver intervention required' with no further advice or explanation.

I'm fascinated to discover what driving technique or situation causes this one to appear.

Graham

 

Jon, the 'cruise control' and 'check rear lights' is classic symptom of a brake pedal switch. We (I use that as the majority of XK8-r members) have replaced theirs.

Gus has a good link on his repair page that makes R&R on it a one-man job, just need a new pedal switch from the dealer... $120, or pull yours out and tighten and clean the contacts on it.

 

I am an engineer but electronic is NOT my strong suit. But my impression is that the onboard diagnostic systems were really just getting off the ground back in the early to mid-1990s and that the CAN system used in our Jaguars was unusually complex due to multiplexing, which I think means using the same signal lines for various purposes rather than for dedicated purposes. Consequently, a problem with X can sometimes trigger an error message for Y.

As an electronics idiot I am probably oversimplifying or mis-stating the situation but I have read several times about the complexity of the systems used in our cars.

Doug

 

Matt,

I looked at Gus' website but I do not see a one-man fix for this brake pedal switch repair. I did see his write-up regarding using a stick to help position the new switch in an effort to fit it where it belongs, and the need for two people to do it this way. Would that be one person working inside the car and one person working underneath the car, or one person working inside the car and one person working under the hood? Maybe it's just me, but Gus' write-up was a bit confusing....

Any pointers would be appreciated, especially regarding how to do this as a one-man job. My best neighborhood buddy with all the automotive experience and massive array of tools (and the very small hands) recently moved to Florida, so I'm on my own now....

 

Jon,

You will be relieved to hear the troublesome kickdown switch Matt mentions doesn't appear on the later 4.2 model.

The throttle position is determined by the APP (Accelerator Pedal Position - item 2) sensor housed under the LH bulkhead cover:



The accelerator cable operates a cam in the APP sensor to send throttle position to the ECM (Engine Control Module).



This is why the throttle limits have to be reset after a battery disconnect to enable full throttle and kickdown to operate correctly.

Graham

 

Graham,

Thanks for your additional feedback and diagrams, but that prone-to-fail brake pedal switch that Matt mentioned does indeed exist on my wife's 2006 XK8. I just checked with two different Jaguar dealership parts departments using our VIN, and both confirmed that this switch exists on our car as part number LJB6420BB. My local Jaguar dealership parts guy told me to call him and reserve one before making the drive over to him because he sells these switches like candy due to frequent failure and runs out of them on a regular basis. He also said that when these switches begin to go bad, the car throws spurious warning messages on the dash just as my wife saw this morning....

Why do you believe that the 4.2 XK8 does not have these switches? According to his signature, Matt has a 2003 4.2, and he says that he has had to replace his....

I surely do not want to purchase a non-returnable electric switch that our car does not have, so some further guidance from you, Matt, and Gus would be much appreciated....

 

Jon,

Here is the early throttle with the troublesome kickdown switch (item 12):



Many, myself included, have had to replace this part.

The Final Series XK8/XKR has a different throttle design:



The kickdown switch has been replaced with a pedal stop (item 9) and sensor (item 13) linked through the throttle cable (item 12) to the APP sensor in the bulkhead.

Although reports of failures on the early kickdown switch are frequent, I have not come across reports of issues with the later sensor or APP.

The comment from your local Jaguar Dealership suggests otherwise and I'm interested to hear which part of the Final Series throttle is failing at such an alarming rate.

Graham