Cruise Control not working.
 

Does anyone know how to trouble shoot the cruise control? 1998 XJ8 4.0
I'm going on a long trip and could really use it..
Iwas thinking maybe a fuse?

Are there any error messages? Do the brake lights work? The brake switch is a common issue. There is a plug with four wires above the brake pedal on my XK8, may be the same for you. Disconnect and clean the contacts.
RJ____________________
97 XK8 Conv. 85K mi

Hi
I have provided the brake pedal switch information in forum thread (post# 8 - has a photo of the part and removal/install instructions):

https://www.jaguarforums.com/forum/x...n-light-76654/

This switch is used for brake lights coming on and off, it is also part of the cruise control system.

Jim Lombardi

at 1. it did tell me that my brake lights were not working. but I check the lights and they were. but I'll check that plug above the brake pedal and clean it up. thank you guys I really appreciate it

I forgot to ask if the the cruise control switch on the shift console lights up.

no the cruise control light does not show up on the dashboard. I put wd 40 on the switch it on the contact and it doesn't seem to be working. do I need to take to switch out and clean it out of the car or can I leave it where its at and just spray it down

I think the button has a little red light but nothing on the dashboard if it's the same as my XK8.
RJ_____________________
97XK8 Conv 85K mi

I just bought a '99 XJ8 and couldn't figure out why the cruise didn't work. The answer was that there is a crusie control master on/off switch mounted just to the rear of the gear shift lever. It's the one one the left that looks like it has a graphic for a tachometer on it, to the left of the one with an "S" on it.

I've seen Hondas with such a switch and always figured it was something the lawyers advised so they wouldn't get sued by someone who made a big booboo. There is no other need I can think of for that switch. I guess you could call it a "safety lock" so maybe it's not a bad idea in some situations.

BTW WD40 isn't very good for cleaning electronic switches except in a pinch. It works at first and them turns into a sludge that isn't good. The best stuff (really the only stuff I like) is Deoxit D5. There is no other product that I know of that is as good. THE stuff for audio connections, the only stuff I've seen recommended over and over by high end music recording gear manufacturers.

On 98's the cruise is vacuum controlled. If you find the brake switch relay is OK (my thought on 1st point of failure as well) check for a vacuum leak or disconnected line. As memory serves it runs from the firewall on the Left side to the the throttle body.

Hi
Here is a PDF on intake air distribution (see page 10 about Supercharger inlet air vacuum feed fuel rail pressure regulator and cruise control system).

Attachment 21687

Also here is a JPEG file showing the SC By-Pass Valve fully installed with vacuum line attached (provided by forum member xjrguy):

https://www.jaguarforums.com/forum/a...s-actuator-jpg

Jim Lombardi

I've got a 1998 XJ8 that is having the Cruise not working. It has the problem that looses power to the little on-off switch. Light won't light up at all when the cruise quits.The Limp home comes on as well. If I stop restart it works right for who knows how long? I can't find anyone who I've found who states the same problems.

I had some similar problems. It wasn't the brake switch. The vacuum lines were routed incorrectly and caused the same issue. I'd look into a vacuum leak or see if the lines are hooked up incorrectly.

Could be.....Prior to it not working I entered a Interstate with WOT. A vacuum hose could have loosened but intermittent? I'll check it out in the morning, thanks!

Cruise not Working
 

Vacuum hoses were good, drove the car 12 miles, after 4 the light on the on-off switch on console went off. The Indicator on dash said of engine problem and limp home. Pulled car over turned key off for 10 seconds restarted and drove the rest of the way ok. Returned home on Interstate and Cruise did well. I've removed battery cable to re-boot to no help....any Ideas?

Trouble shooting the cruise control system is a bear if there are any codes. Since CEL and limp home were displayed there is a good chance you have a stored code or two. Have the codes read by one of your local auto parts stores.
If there aren't any codes you will have to use the circuit diagrams from JTIS21, which you can download from the sticky's.
You say the light on the cc button is out when the failure occurs. I checked the electrical guide and found that the switch is powered by the GW wire from fuse #14 in the left hand healboard fuse box. Check there first. If you have power there and the the light is out, you may have an intermittent fault in the switch.
That at least gives you a starting point.

I think you've lost the codes when battery disconnected.

I'm not sure all stored codes are lost, but apparently he can generate them again if they are.

Ok, The light on the Console comes and goes with the operation of the Cruise. When the Limp home is lit up, the light on Console is off. When the Console light is on, the Cruise works fine. The possibility of a Vacuum problem doesn't seem likely because of the intermittent deal.

We are dealing with cause and effect here. When you are in limp home cruise will not be available. If cruise is not working when you are not in limp mode, then there is a problem with cruise. Did I make this confusing enough? I hope not.