Hello guys,
My XJ6 X300 1997 4.0 liter cruise control stopped working for unknow reason. When I turn on the cruise control, it lights red which means it's working, but when I click the button that takes the current speed, nothing happens. I was wondering what would be the cause? Could it be a fuse that is burnt?

 

Mine too a while back. Awaiting instructive responses!

 

I don't have time to check the electrical diagrams now, but if there is a brake pedal switch like the XK8 and XJ8 that is a likely culprit.

 

Vacuum hose adfrift from actuator under the bonnet ?

 

Hi yahyazz2zz,

As RJ mentioned, there are two brake pedal switches involved in the cruise control, the Speed Control Brake Switch, and the main Brake Switch. If your brake lights work properly, the main brake switch is probably fine, but the speed control brake switch could be faulty.

The system is vacuum operated, so melhookv12's suggestion about a vacuum hose being disconnected or cracked is another good possibility.

A very common failure point is the dump valve, Part 2 in the diagram below. It's mounted in the left front of the engine bay under the relays, near the cruise control vacuum pump (Part 1). The dump valve's default mode is to pass air, but when 12V is applied, it should close and hold vacuum. Its purpose is to immediately release the vacuum when the brake pedal is applied. If the dump valve fails and will not close, or if there is a problem with its power supply, the cruise system cannot work. You can test the dump valve by blowing through it when unpowered and then again while applying 12V.





Failure of the vacuum pump or its power supply is another possibility. Also the cruise actuator, Part 3, which is mounted near the throttle body. Failure is rare but you can inspect the bellows for damage and test the actuator with a hand vacuum pump.

Cheers,

Don

 

if the black rubber boot #3 the actuator is cracked or broken cruise wont work

 

if this is craked or broken cruise wont work it call cruise control actuator

 

I can confirm that if you have a rupture in the #3 cruise actuator the cruise control will not work. Happened to me. On the to-do list.

 

My cruise control stopped working some months back. As I don't do much driving now where I would make much use of it, I did miss it somewhat and hated having a facility that wasn't working, but decided to live with it (or rather without it!). Checked this thread and examined the cruise control actuator but couldn't see any problem with it so guessed the fault was with other harder to access components.
Anyway as I've a journey coming up where CC would be so useful I looked in the engine bay yesterday at the cruise control actuator again. It looked okay as before, but when I shone a torch around it I saw a tiny, tiny hole in the rubber surround.
Hopeful that this was the problem and with fingers crossed, I found some strong rubber adhesive and spread this in the area of the hole then stuck a piece of black insulation tape over this and then another layer of adhesive. The adhesive is supposed to set in two hours but advises 24 hrs for full effect.
Anyway, this afternoon, just been out in the car, clicked on the CC and it's working!! So now I know where the fault lies and the part to replace.
All thanks to this site and this thread. So a big thanks to those who contributed their advice and illustrations. Really appreciated.