Hi I have a lovely 2002 XJ8. It drives beautifully and is in good condition except for… it will drive for 2 hours and then go into fail safe and won’t turn on for hours. I’ve had it in three mechanic shops. They’ve been through the wires. They’ve even put a new computer. They have done everything they can and cannot figure out why it does this. At this point I don’t know what to do or how to get rid of the car. I love this car and I’m sad (it was my mothers and i got it when she passed.) but I owe the mechanic $1100 for new parts and they are not charging me labor which would’ve been several thousands of dollars. I don’t know if this is something I sell for parts or how to do that. But it’s the end of the line for Jaguar unless somebody wants to try it has a project. It’s really nice and drives so smooth and is comfortable and all the good things. But It’s just unreliable and no one can figure it out. Any suggestions? How to unload for parts or sell? Thank you. - in Denver CO
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When you say it won’t turn on, does that mean the car is 100% dead when you turn to key position 2? I know you’re past the fixing it stage but, I would check to make sure the battery bar isn’t (trust me on this) overtightened. It’s getting more common that the positive and negative braided battery cables are failing due to internal breakage. Check the connections at the mega fuses for clean and tight mountings in front of the spare tire. Check the bulkhead battery connection in front of the engine ECM. Don’t give up just yet.

 

It turns on but then eventually goes into transmission fail safe and won’t start for a period of time. It’s been through three Jaguar mechanics and in a shop since September and had multiple visits before because it wouldn’t act up in front of them for a long time. Its had a complete wire tracing and a new computer and other things I don’t understand how to explain. At this point I need next steps. I have to pay for the parts and I can’t keep a car that I can’t get fixed.

 

The brake light switch seems to be the issue for many who have reported these same problems.. That switch must tie several circuits together including the cruise control.
It may be a "long shot" but see if your cruise control is working and if not working properly, it could be brake light switch at fault.

 

What kind of mechanic was messing with the car? If its not a Jag mechanic you’re dealing with a situation that could leave you feeling hopeless. Dont let this get you down. So what’s interesting is that it happens after 2 hours of driving. Are you driving for over 2 hours often? I know that I can drive for many hours.

 

2 of the mechanics were Jaguar only specialists, one who specialized in classics and anything pre 2005 (they have rebuilt many from the shell), and another mechanic was a transmission specialist. He was a go to for Jag people here. At this point, are there any suggestions on how to offload (respectfully) the car? It’s got to be great for parts. Unless someone wants to buy it and keep trying.

 

This may have already been addressed but is there any change in the way it runs in fail safe mode? Does it sputter or misfire or does the throttle act strange (other than the RPM being limited)? I had similar issues with my dad's 98 XJ8 and after replacing the ground straps, battery cables and brake switch it still would randomly go into failsafe mode but independent from the cruise control so that part seemed fixed. Ultimately I replaced the throttle body with a used one as it seemed to coincide with random surging/sluggishness. Since then it hasn't reappeared. Considering it has 170K and the previous owner was pretty rough on the interior he didn't want to invest a lot. I believe the TB can be rebuilt (several online rebuilders) if you go that route and want more assurances. The 2002 has an electronic throttle whereas the 98 is vacuum assisted. I believe the later throttles could have issues too.

If you have Jaguar experts working on it, they may have already ruled these issues out. I'm no mechanic but I usually start with the simplest solution and move from there if I can't pinpoint it. The ECM would be the LAST resort for me unless everything was ruled out. Maybe these guys did some advanced testing and found some ECM errors.

Just sharing my meandering experience but I am curious what exactly led them to the ECM. If I missed the explanation my apologies. Best of luck, I want as many of these on the road for as long as possible.

 

Can you post on here what engine and transmission codes you get when failsafe occurs?

When the car dies and you turn the key off and then back on again, you get a digital readout on the instrument cluster yes?

When you go to start the engine, does the engine crank over?

 

unload the car eat the loss

you can’t diag this over the internet and it may be out of your local tech’s skillset

 

We know that the failsafe mode kicks in to prevent further damage to the car when it detects a fault. It is true that the warning light is quite vague and can point to a number of issues.
The failsafe mode is computerized and thus, any fault that is detected in the car by the computer system can cause the car to activate it. It seems the most obvious faults that cause
the failsafe mode to come on are normally found in the systems pertaining to the transmission. That system is responsible for controlling the speed and direction in which the Jaguar is
driven. The system is made up of several different parts, any and all of which can be culprits when the failsafe light comes on. Also, when any of the other vehicle functions that are
computerized develop a detected problem, then the failsafe mode can be activated. There are a lot of sensors that control things like the pressure of air in the engine, for example,
can also trigger the light. Because the failsafe mode works based on the car’s computer, a fault anywhere in the electrical system can also cause the computer to misread situations
and this can cause the warning light to come on. Such faults could arise from even a blown fuse or maybe a problem in the wiring harness.

Given that in your case, the failsafe kicks in only after being driven a while, I would focus attention on the transmission, or engine cooling areas of the Jaguar.
When the vehicle’s transmission system goes into failsafe mode, the immediate effect is tha

 

UPDATE: Car went in for transmission work and was basically stored for 2 years. However... The mechanics found there was a security glitch that actually had to do with the key fob... where clicking the buttons back and forth took it out of fail safe mode. Installed a newly refurbished computer. Car drives smoothly. However,
since its been sitting ... other (more minor) items need to be addressed. Its a beautiful car, but I don't want a project (not my lifestyle). So I will be listing it in the for sale section. I just wanted to post this because I'd never heard of the security issue related to the door and key fob. The mechanic found this out by accident while fiddling with the fob.