could be a bunch of things. check the codes.

 

keep us updated with the problem

 

any codes???? possible throttle body due to the fact that the cruise inop.. but there wud be codes

 

Mine had the same problem, and unfortunately, I did a couple things all at once, so I'm not positive which fix actually fixed it. EDIT: My Failsafe would come on when I tried to activate the Cruise Control.

I sprayed the brake switch with WD40 to get the contacts working again (I believe this was the actual fix).

I cleaned the Air Cleaner, Throttle Body and MAF sensor.

I cleaned the breather hole on the driver side valve cover. While doing this, I noticed a small crack in the vacuum hose leading to this (Might also have been the problem). I applied black silicone sealer to the hose since replacing it meant removing it from under the SuperCharger, and that did not look fun. This hose was VERY brittle, so will probably fail again some day.

Good luck, and I hope something in this thread helps!

 

I don't have a solution for you, but here's the info that JTIS has for your code:

DTC
P1643

Description:
CAN TCM token missing

Monitoring conditions:
Ignition ON > 5 seconds

Default Action:
When fault is detected, ECM:
– Limits throttle to 30%
(Torque reduction request data
missing results in harsh
transmission shifts)

Possible causes:
CAN open circuit fault – TCM to ECM
CAN short circuit fault
TCM failure
ECM failure

The other code you can ignore--one of either P1000 or P1111 will always be present and aren't trouble codes.

TTYL
David

 

The Brake Light Switch is found under the dash connected to the Brake Pedal arm. I never even removed it, just soaked it a LOT with WD40. Spray into any openings you can find. Be sure to place a thick towel underneath it to protect your carpeting and interior. It will drip for a while after doing this, so be sure to leave the towel there until it's finished.

I've done this to many other vehicles in the past and benefited from a few more years use from them before having to replace. Sometimes replacement is the only option due to broken internals.

Attached is an image of the switch.

Just for future knowledge: I use the same method for MANY parts in a car or bike. Door Lock Actuators that don't seem to work anymore, Dome Light Switches in the Door Jambs and Latches, The Trunk Light Switch in the Latch Mechanism, Door Latches, Slow Moving Electric Windows, etc, etc... Sometimes this is only a temporary fix as some items truly need to be cleaned and re-greased. But for this specific switch, it's a permanant fix as long as the switch continues to operate.

 

No problem. By the way, the only reason I cleaned my switch instead of replacing it is because a normally $20 switch on my other vehicles is $50-100 for this car.

Just to be absolutely sure, you could always do a continuity test on the switch to be sure it's working. If not, then replacement would be your only option.

And, as others have mentioned, it could very well have been my throttle body cleaning that fixed it. Either way, all of these maintenance items should be looked after anyways.

I would suggest you look at this thread and follow the link in the first post. It leads to an Adobe PDF File, and is the best tutorial on how to clean these parts that I've seen to date. It's for an XKR, but it's pretty identical. Thanks to Mrtexasdan...
https://www.jaguarforums.com/forum/s...+body+cleaning

Good luck, and let us know how it goes.

 

I had the same problem ( the engine fail safe mode came up when i tried to turn on cruise contol) as "SuperSport" said you should check all the conections around your throttle body and double check all the hoses (small ones) if any of the hose has crack then there is no vacum and no cruise controll.... all those small hoses fom getting old are becomming realy "cracky" so even when you try to move it you may brake it... so buy a meter of hose (inside diameter of the hose is 6mm as i remember) and change all defected ones... good luck

 

Thanks SuperSport, the WD40 trick on the brake switch worked great. I sprayed the switch liberally, let it drip off for about twenty minutes then took the car for ride. The failsafe light came on as usual after a few miles then went off after cycling the brake pedal a few times. It's been two weeks now and still no return of the failsafe indication. My only question is, what lead you to try this in the first place? Seams like SWAG at best. Thanks again for the suggestion! I do not think I could keep my Jaguar XJ8 going without this forum.
T

 

Reading these threads lead me to the brake switch being a possiblity. Other members shared that info. But cleaning it with WD40 is something I've done for many years. Sometimes it works, and sometimes it doesn't.

 

the throttle by sensors are bad if you have it checked the codes should read p0120 fault position and throttle position will come up this part is very expensive since you cant just but those two small parts you have to buy the whole throttle body easy to replace in your garage but look for a used one for about 100 to 600 dollars. Have a reputable mechanic check it out first

 

Had the same problem on my wife's 2000 XJR. Engine Fail Safe light comes on. Cruise control stops working. Initially was intermittent, then consistently would come on after only a couple of miles of driving. Had codes checked and they said "Brake Light Switch" was bad. I followed her to the shop for the repair and noticed that her brake lights came on after a couple of miles. Called her and she said the Fail Safe light just came on. Of course we all know that stepping on the brakes kills the cruise control so I was confident replacing the switch would fix the problem...and it did. (Repair made July 27, 2015).