Failsafe comes up at random,could be 100 metres or 60 kilometers..but would appear that with the "cruise" off failsafe does not come on. Cleared codes via OBD and a transmission code that was there has not returned. Following a OP post checked the brake pedal switch and was fine,
OBD now saying ALL seat and door modules are "Faulty" but not showing as a code..
When cruise is ON it will not engage but repeated "advance speed" will make a small surge trying to increase speed.. Got me buggered!! Maybe an earth problem within the cabin area?
Any advice would be greatly appreciated. Nearest Jag garage is 350K away so trying to isolate this myself. There must be a connection with the cruise and failsafe both talking to each other!
Cheers,Neil.

 

Just went through such strange happenings myself. My issue turned out to be the cruise control button micro switch. The problem randomly occurred with cruise button up, never with button down. Exercised the button a number of times before pulling the console apart and so far the problem has gone away. Why that micro switch would be linked to random messages escapes me.

 

Here are three issues I experienced while owning my XJR with similar symptoms, including happening more when Cruise Control was turned on.

First repair I did was the Brake Light Switch. Failsafe Mode went away for months. Then returned.

Next was to clean throttle body and Part Load Breather. Also would fix issue for a while, but only to return later.

Last and permanent fix was the Throttle Position Sensor connection. I did the fix listed HERE, but wiring in new connectors is the known way of a permanent fix.

Try to unplug and re-plug the connection and see if the problem goes away for a few weeks. If so, I would suggest you fix the connection using one of the above methods.

PS: I rarely got a trouble code, only Failsafe Mode, or rough running.

 

Ah fun this one! ;o]
Had the very same problem....after repalcement of two TB's (under warranty, it all dissapeared.
Only happens with cruise engaged.
Turns out my TB's could have ben fixed by the 'replace pins' routine on the TPS connector.
I am not a great fan of cruise anyway so, don't use it.

 

Don't use it xjay8 ? Maybe where you are thats possible.Can you keep your car on a steady 100 kilometres for a few hours without going 2 kilometres over that mark? I cannot. I will pass several randomly placed and sometimes disguised roadside speed cameras every time I go for a drive. These ******* things send you a $175 speed ticket at 2-3 K's over plus a demerit point.10 K's gets you $290 and three points (you start with 12 and they have to last 3 years) and when you have 12 start walking for 3 months (which I have 3 times now)
"Cruise" is the most important button on the car for a comfortable drive.Although I get better fuel consumption without it. Thanks for the information,I do appreciate the input.

 

As far as I can tell XJAY8 was relating his own experience. There was no suggestion as to what you should do personally.

 

Yes he was Plums. "I am not a great fan of cruise anyway so, don't use it."
I did not mean to oppose his choice in any way. I apologise to xjay8 if it appeared that I did,that was not my intention,but to emphasis the importance of Cruise Control to me.
Hard to type in the right tone of voice. But reading back I can see it looks condescending.

 

No problems Gippsland...nmo offence taken ;o)
Your lovely police state definately needs cruise or a very judicious foot ;o)=)
Even on my trip to WA and return in'09 I never used cruise....perhaps that's why I was slugged $390 by a highway patrol outside Kimba in SA ;o)=)

 

SuperSport,

The contact cleaner and conductor pin saved the day. Clive, my wife's 2000 XJ8, X0308 has been giving her fits for the past several months. With a trip to Radio Shack and the purchase of connector cleaner and a contact pen, Clive is acting alot better and my wife is a happy woman. Thank alot for the work and the post.

Regards,

Thomas
2000 XJ8 - X308

 

Thomas....you're right, it's usually the simplest things that can upset the apple cart....including women ;o)=)
It is always far better to attend to the simplest things before throwing mega bucks at the problem.

 

I had a cracked vacuum line at the fpr that caused that same problem on mine also...