Hi

I have an issue with my cruise control. There is a very intermittent issue with it, more often than not it is not functioning but sometimes it comes back to life for a short period of time.

I have checked all that I can, electrical connections, vacuum hoses etc, all seems to be ok in that area.

Having had a discussion with another owner a little while ago who had the same issue, he had his ECU tested and a fault was found, fixed and all seemed well for him after..

Does anyone know of a reputable ECU tester?

My ECU code is LNC1410CA.

I have tried a number of companies and they all say that they cannot test the unit... Someone must be able to!
The only other thing then is to try a unit that is functioning 100%.. but presumably these need coding onto a car?

Thanks in advance..

By the way, no codes are being thrown, only the cruise control is not working...

and the brake switch is working...

Dan

 

There is a diagnostic test sequence in the JTIS for trouble shooting the cruise control circuits from the buttons on the wheel through the clockspring to the ECU.

I had an intermittent fault and it was in the ground connection which runs from the cruise control buttons to the radio buttons on the opposite side of the wheel, then to the clockspring connection.

Your problem is not likely to be the same, but the test procedure will check it out. The wires make some very hard bends in the area of the buttons.

As to the ECU, it's possible to have some corroded connections so it would be worth the effort of cleaning cleaning them with electrical contact cleaner. If you do want to have it tested contact ASI in Tennessee, US. Link below.

Automotive Scientific Inc. | Quality Rebuilt Automotive Electronics | Rogersville, TN

 

Hi

Thanks for that

I have access to JTIS, can you expand on where the section is? That may be very useful to go through to make sure that i haven't missed anything...

 

I don't have the laptop with the JTIS here right now. Navigating is a little difficult until you get used to it, and I don't recall exactly how to access that test.

 

Section 310-03

 

If it was me, I would revisit this brake switch. It is a common failure. As you probably know, it is actually a pair of switches activated by the same cam. One is normally open, the other is normally closed. The ECU can detect when they are not in opposite state and eventually throw a message. That being said, I am not sure how quickly the message comes up, and how quickly the cruise control disengages. Is it 1s, or 10 minutes? Normally, those switches go bad gradually, and have erratic behavior for a while. So it might test ok in your garage, but fail a bit later on the road.

FWIW, I believe the ECU can issue codes for this problem, if you have a Jaguar-aware code reader. These codes most likely reset every time the ignition is shut off, though.

Some folks have re-soldered the individual switch leads to the board, others have located the exact micro switches, and replaced them. I have replaced mine with a new one a while ago.

Best of luck, keep us posted.

 

I agree with checking the brake switch first.

Gus
www.jagrepair.com

 

Hey

So to update on this..

I finally got round to digging out my old laptop with JLR SDD on it, its an old version and sucks to work on.. Incidentally what is the latest version that will run on an 1999 XKR?

So I ran through the testing of the buttons on the steering wheel. SDD also allows you to test for the brake switch... both are working as they should be with no faults..

Also the car does not have any fault codes showing.

I have tried two different cruise control buttons... neither work.. neither show the red light.

Solenoids are working as i tested them by running 12v through and you can hear them open and close, and the vacuum lines are working fine and i can find any leaks.

Does anyone know the pinout to the cruise control button so I can see if voltage is getting there or if there is a ground issue?

The only other thing to do is test the ECU or refresh it... Any other options?

Thanks

Dan

 

You can download the electrical guides for the pinouts here: JagRepair.com - Jaguar Repair Information Resource

 

ok, saw on another post

On the early XK8s, the cruise control is vacuum operated with a couple of electrical solenoids. Power to these comes from the ECU via fuse #10 (5 amp) in the ECU fuse box.
Check this fuse, and also the vacuum hoses - one from the top of the throttle body, and one from just below the right hand side manifold.'

i have tested this and get 12v.... Next?

Thanks Bladerunner will have a look

 

Well i have earth and I have power to the switch.. just need to check the wiring going back to the ecu now...

I still think the ECU thinks it doesn't have cruise control for some reason... can add tell it to reconsider this as an option? lol

 

Do you have diagnostic software (SDD/IDS)? If you have that you can check that it's enabled.
But as the problem is intermittent I think you need to be looking for a bad connection.

 

So, spent a lot of time with JLR SDD... checking this and that... Conclusion?

There is a break from the speed control switch...

It does give me a code.. Break connector. FC063.

I suspect that that just means that theres a break in the wire.

It is the wire that goes from the cruise switch to the ECU. Does anyone know its route? or if i can just bypass the old wire and place a new wire in its stead? Id obviously like to trace the wire and see where it goes but I have no idea where it goes.. it disappears under the gear selector switch and I have no idea where after that.

JLR SDD says brake switch(!!!!!!!!!) is good! Steering controls are good...

Just need this wire.. have had this for the 5 years I have had the car... I'm soon close!!!!!