I am still trying to sort this thing out. It was working for a while, but quit again. I need some expert help before I take the steering wheel off.
There are two circuit wires and a ground from the cassette. The circuit wires are s/r and s/g and go to connecter 10 of the ECM. With power on I read line voltage at both pins whether cruise control is on or off. When I disconnect the battery and pull the connecter there is no continuity between the two pins when I press the set button. Am I oversimplifying The function of the buttons? Or is the problem in the button or cassette wiring?
RJ ________________
97 XK8 85K mi

 

What is it doing and not doing? Hard to identify the problem without knowing what is taking place. Do you get any codes?

 

The behavior you describe is expected.

While disconnected measure the resistance as follows:
BO to SR, Set- should be 680 ohms when pressed, Set+ should be 430 ohms when pressed.

BO to SG, Cancel should be 680 ohms when pressed, Resume should be 430 ohms when pressed.

Check that you have a good ground on BO.

If all that checks out your problem is not with the clockspring cassette or steering buttons.

 

The contruction of the cruise control switch on the console is a bit lacking. I wouild definitely be suspicious of that.

 

Gus, sorry for not mentioning, no codes. Steve, thanks for all that. I'll go after it tomorrow when the garage is cooler. It's in the basement, but even so it's upper 80's in there this afternoon and I have a cold just to aggravate the situation.

 

The console switch and brake switch both check out.

 

The garage has cooled a little. I removed the airbag and find 3 wires coming out of the cruise control module. I assume these are equal to the sr,sg and bo in the wiring diagram. I'll check them first in the morning before taking the wheel off.

 

The control buttons and cassette check out, but still no cruise control. I can read the power on/off at the ECM so the console switch is working. In fact, everything is working as it should right to the ECM. Could it be that there is no input to the throttle from the ECM?
I do not look forward to a six hour trip without cruise control, I'm getting too old for that.
RJ

 

Do you have JTIS? Section 310-03 contains speed control troubleshooting charts.

 

Does the XKR/XK8 have the controls on the steering wheel? My ls has this problem and it is the clock spring which is broken.

 

Amerituner- the cassette is the clockspring and it is OK.

 

I have looked through JTIS 310-03 and I have already performed the majority of the tests. I will have to set up a plan to go through all of them. What bothers me about the JTIS is that my Autoenginuity software should display a P code if any of those faults have occurred, but I don't have any codes. When I go to the dealer to get a spare key next week I'll ask them to check.
RJ

 

I think I am finally headed in the right direction. The cruise control vacuum switch on the throttle body is not being activated. XKR Racer explained where to find the solenoid in the fender well and I will test it tomorrow morning.
RJ

 

Please let me know where the solenoid is as well. I have an intermittent in cruise control as well and I was suspecting the vacuum to the throttle body.

 

Just take the liner out of the right front wheel well. All three solenoids are towards the rear. Test the solenoids by removing the plugs and applying batt. voltage. I removed them from the car and used my trickle charger with a couple of test leads.
Unfortunately, mine all work, so I need to look elsewhere. I'm still not sure if I have vacuum at the throttlebody switch so I'll check that tomorrow.

 

I decided to check the vacuum system. By running a tube into the passenger compartment from the fitting that slips on the vacuum control on the throttle body I was able to determine that there is no vacuum. In fact, I was able to suck air through the tube. I then determined that there was line voltage to all three solenoids from the ECU when the ignition is on.
Confusing- There was vacuum in the accumulators next to the solenoids, the solenoids all work when bench tested, there is power to the solenoids when the ignition is on. I'm missing something.
RJ

 

Yep! You are missing the possibility of a failed or more likely intermittent brake pedal switch. It will likely set a code P1571, but generic scantools generally can't read it. The default for that failure is no cruise control. Many times a key off and restart will give you cruise control, until you try the brake, when it will register the fault and kill the cruise.

Just a thought.......

 

No, I'm using Autoenginuity and can read P codes. Also, I have repeatedly checked pin EM10-11 on the ECM which receives power after the brake switch/cruise control switch. That doesn't eliminate the possibility that not enough current is available to activate the vacuum solenoids, but I don't think there is much chance of that being the case. maybe I'll try bypassing both switches and see what happens.
RJ______________
97 XK8 85K mi

 

You might try removing and cleaning up the two ground points in each enclosure, one by the brake booster and one over by the coolbox. I've had those give me cruise and EMS trouble.

Cheers,

 

I checked the voltage at the three solenoids today. Two of them are grounded through the engine management fuse box and read 0 V with the power and CC on. The third is grounded directly and reads 9.1V. This one appears to be the control for the CC vacuum and maybe the voltage increases when the CC is operating, but 9.1V is not enough to open the valve. I have buttoned everything up and resigned myself to waiting until I get to the dealer and see if they can sort it out without replacing everything.