Ok I need some opinions, I have a 98 xk8 with the failsafe message, the car runs fine, I have an appointment at the Jaguar dealer on Tues. to have them run diagnostics for $140, but I thought I read somewhere that with out a code they would only be guessing. I have plugged in a scanner and there were no codes. So is it worth it to pay to run diags?

 

The dealer has software that can query modules other than the engine control unit and can read codes other than the OBDII codes required by federal emissions standards. So, they should certainly be able to diagnose a RP. Does your cruise control work?

 

The cruise control doesn't work, the red light on the console comes on, but the cruise doesn't seem to engage. When the failsafe mode comes on the red light goes out. I just bought car so not sure if cruise worked before or not. Are you thinking it might be the stop light switch? And if so would you change it or go ahead and let them do the diags? I think the price of the switch has gone up drastically, I've seen it up near $200, autozone has one for around $90 if it works.

 

Well, I can't answer for what I would do since I have already invested several thousand dollars in the dealer level software and I would just diagnose it myself! I would say depending on how much trouble it is to get to the dealer, it might be less trouble and expense to just have him diagnose it. On the other hand, the symptoms sound very much like a bad dual brake switch is the correct diagnosis. Crap shoot?

 

Would the dealer software call out a bad switch? I don't mind paying for it if it can pinpoint the problem, but if he will just be guessing like I am, then I would rather just try a switch. Also have you heard of people having good luck with the autozone switch?

 

I would suppose a switch is a switch, but I really dunnoh. Yes, if the dealer puts a competent tech on it, he can absolutely call out a bad switch circuit, which means a bad switch unless there is a highly unusual case of a bad connector or bad wire.
BTW, the bad brake switch diagnosis is better than a "guess", closer to a "bet".

 

I had the same problem. I got a new brake light switch from the dealer. I don't recall it being too expensive. However, after pulling out the old one, I wished I had done that earlier, for I could have just cleaned out the electrical contacts instead of buying a new switch. The other way to temporary solve the problem is just to turn off the cruise control completely. For some reason, the brake light switch, cruise control and failsafe mode seem to be related to each other.

 

The reason they are related to each other is that the brake switch disables the cruise control and Jaguar used a second switch as a redundant fail safe control to assure that a single point of failure (the switch) would not result in failure to disable cruise control when braking. There is similar design in the throttle body. If the news reports are accurate, some Toyota owners probably wish Toyota would have used the same design practices.

 

See my earlier post. You guys might laugh, but I used my local Big-O tire store. Diagnosis was free. It said brake light switch. They replaced the switch (bought from local Jag dealer) and replaced it for $318.27 which included a synthetic oil change. No more warning lights and cruise works find now.

 

Cleaning the switch with WD40 as talked about on the first page of this thread is SUPER Easy, and almost FREE. Worth a try to see if that's it. Those switches are susceptible to getting dirty and not always being broken. If you still want, you can replace it if cleaning takes care of the problem.

For what it's worth, I owned a Prius that had this issue. It was actually when the High Voltage Battery Circuits had issues, the car would REV very high. Of course, the Prius was not super powerful, so I was always able to stop it, but for someone who was not comfortable with Surprises, I can see how it could cause an accident. Toyota claimed this didn't happen, but I can confirm it DID! It was easy to replicate...

I'd never laugh at saving $150! Although, I would have saved the other $300 and replaced it myself, but I'm sometimes cheap.

 

I found one on ebay for $40, will try that first and reschedule appointment with dealer if that doesn't work. Will update.

 

Sounds like a reasonable plan. Then you will return and report your results, right ?

 

Ok I am a very excited jag owner. I got the car a week ago today and have fixed the seat module, sent the mirror back for repair, and just installed the new brake switch and the failsafe mode seems to be gone and the cruise is now working. Thanks for your help and thanks to all the people for the other posts that helped me get here. The problem with the old one appears to be the ratcheting part was worn and it would not always return to correct position.

 

Awesome News! I always love when things work out. These forums are invaluable when you own a special car like this. These guys taught me SOOO much.

 

Hi All!

Recently the Failsafe mode light has illuminated on my dash three times on my 1998 XJ-8. Once it happened when I drove through a deep puddle after a storm that caused water to gush up the right wheel well. Today it happened as I was driving in a misty rain. I can't remember if I had applied the brakes before it started today, but I feel sure I applied brakes when I hit the puddle. I can turn off the ignition for a few seconds and my car starts back up and clears the warning. I will try to pay closer attention to my driving if this occurs again. Thanks for the posts. It seems I have a new issue every couple weeks now....

 

Obviously, the brake switch is a candidate. Might also be a frayed wire on one of the wheel sensors since it seems to be caused by water.

 

The brake cruise control cancel switch is the culprit.. I was driving a couple days ago and tried to set the cruise control...it did not activate. I noticed the light on the cruise control switch at the gear lever was still lit. I then lightly pumped the brake pedal and tried the cruise again..it started working. I have done this several times now, so I am convinced it is the switch on the brake pedal.. Here is my question: I drive a 1998 XJ-8 and I noticed in the wiring diagram there are two brake switches shown. One controls the brake tail lights and the other cancels the cruise control. What is the correct part number ?

 

There's a great video on YouTube in which a guy from Tennessee sent his throttle body to be rebuilt at a place in East Tennessee and it totally fixed the problem. Check it by doing a YouTube search for Jaguar Fail Safe Engine Mode.