I have aproblem with my 1998 VDP XJ8
I have owned it for one year with o problems.
Last week I replaced the battery because of a internal short in the battery.
A few days later while driving I had my cruise on and then it went off and gave me a engine failsafe mode light.
I turned off the engine to see if the error would clear and it did for about 15 minutes.
The next day I drove about 70 miles ad at about the 50 mile point the light came back on and the cruise stopped working.
At my destination I disconnected the battery for about 30 minutes to clear the code from memory.
On the trip home I didnt use the cruise and I didnt get a light.
Today I am going to drive with the console cruise switch on but not activate the cruise to see if the light remains off then later with the cruise operational
I also spoke with my Jag tech ad he told me 2 other people had within the last week reported the same problem.
Is it possible that bad air would cause this problem?
We have had 2 days of very bad dust amd smoke filled air that blocked out the sun to the worst degree that I have seen in my 25 years of living in Arizona.
My tech said it is not posting a code and he has no clue as to what the cause is.
PLEASE HELP

 

And, the answer is... check the brake light switch. I don't know if the same circuit is used on this car for the lamps and the cruise control circuit, but it can give that behaviour. Check and see if the brake lights are working after you have the problem. Check the archives, or, hopefully, someone else will chime in with the correct reoubleshooting diagnostic procedure. ( I do not have access to the manuals at the moment)

Bad air? Common now.

 

Had this with my `98 XJR. It turned out to be a plastic 4way connector on the vacuum lines that are directly behind the throttle body under the central plastic cover that had got brittle and snapped. had the same symptoms as your car, and it threw no codes.

 

Andrew thanks for responding to my question.
Is it possible to take a picture of the area and lines you mentioned?
Vic in Arizona
vtmeek@gmail.com

 

Will take some photos tomorrow. Has just reminded me that I bodged this connector about a year ago when it broke, should really put a proper connector in.

 

Well, I have taken some photos, but the I.T. department ( A.K.A the kids ) are not coming round today, and I have NO idea how to post them. If you take a vertical line through the windscreen wiper spindle down to the bracket on the bell housing that holds the o2 sensor plugs, the connection is about halfway between. the vacuum hose at the bottom has a white trace, and is in a + as opposed to a x orientation.

 

My 98 xj8 recently did this the day after having my rad repaired! Things always seem to happen right after u spend money (has me a little Leary) I've owned my car for a few months now and this is first time I got the failsafe engine mode! But I found if I leave key in on position, and just jolt the shifter in park a little! The light goes out and she starts! That's just my case! Looks like time to spend more money lol

 

Yesterday I drove 120 miles half with the cruise off and no problem.
The second half with the cruise on about 50 miles into the trip the cruise dropped off and the console light went dark and the cruise would not come back on.
I check my brake lights in this condition fine
The failsafe indicator was on...cruise light off...no reset for the cruise.
I turned the ignition off and back on and the cruise light came back on and the fail indicator was off.
I dont know if loosing vacuum would cause the cruise light to go off.
Any ideas?

Andrew when you reply page down to additional options and click on manage attachments to upload pictures

 

I have the throttle body, supercharger etc removed because I have to renew the heater hoses. but hey, it gives a clearer view. the connector you are looking for is the red dice in the photo. Mine was broken so I made a temporary one by drilling through a dice and gluing some plastic tube in place. It worked that good I forgot about it until this thread.

 

Just a thought, it may be all transposed to what you have, as my car is right hand drive. Hey, it worked... can post photos without needing young people. thanks vicsrc.

 

there's two microswitches within the brake pedal switch assembly - one for the rear lights, the other for cruise. If the microswitch is faulty this causes limp mode in cruise, far far more common than Andrew's obscure fault, I'd suspect Ross has put you onto the correct fault diagnosis.
Our resident archivist Jim Lombardi has put a superb thread together here so you don't have to do much else than call for a new part and fit it. No biggy.
https://www.jaguarforums.com/forum/x...switch-102921/

 

I replaced the brake switch this morning and I only have 80 miles of stop and go with the cruise and no failure yet.
If posible I would like to list where I got the switch from.
When talking to the sales person he assured me that the switch was new a original Jaguar parts no after market part.
He also said that the part was guaranteed for life AND here is the thing that blew me away!!

Send it back if it does not solve my problem...

Jaguar Brake Light Switch - Genuine Jaguar LNB6420BB | FCP Euro

 

I got away with using circuit board cleaner, then alcohol followed by high pressure air. now works fine
used a sewing needle to peel the red rubber seal back,
if anyone is interested cruise uses the two outside pins on the plug. They are normally closed, and the circuit is broken when you depress the brake pedal, and that's how I tested and diagnosed mine. thanks for the help