Any codes may help.

 

Upon further reflection, I should make it clear that a cruise control malfunction will not result in limp mode. You have another problem and should investigate before taking a trip.

 

I think what RJ237 is saying is cruise malfunction does not set true limp home & I agree. I've lost cruise 2 times in 14 years. My symptoms were the same. Both times it was a bad brake microswitch.

Your symptoms are in line with the usual suspects - bad brake pedal microswitch or vacuum leak (cruise only used Vacuum on 98's and perhaps a few early run 99's). Neither of those set any codes when they are the cause as with those faults Limp Home is not actually set - ie you get the dash lamp, but the power train is not put in limp home. (transmission shifts normally, etc).

So ... if no shifting issues, codes, or other obvious signs of a bigger problem, go back to the 2 common causes - the relay on the brake switch or vacuum. If cruise failed under WOT, it is possible a vacuum hose gave up.

I would pull any codes and if none, look for a split on a hose, not one completely off, & would focus on where the hose terminates at the solenoid on the firewall as many other posters in the past have found the trouble there (Left side, behind the brake master cylinder). If none, then check to connector to the brake switch to make sure it is making contact OK & if nothing there, replace the brake switch.

 

Usually it's kinda the other way round: limp (or restricted) mode suppresses cruise.

 

Ok, The Limp home mode comes on and or the Cruise quits. I will be driving along with or without the cruise on when the Limp home comes on and the light on the cruise button goes out. It will all be fine after I stop, turn the motor off and remove the key for a few seconds.

 

Now I understand. The failure of cruise is just a symptom, something is causing the ECU to put the car into limp mode. It is unlikely that it could go into limp mode without leaving a code. You need to get the codes read, either at a local auto supply store, or buy a reader yourself. When you have the codes, report them here and we will help interpret them.

 

Thanks, I did check the codes and came up with P1000. That didn't help any. I've driven about 100 miles today with having to stop and turn off motor at least 6 times. That entailed Interstate driving as well and no Engine error at all and used Cruise as well.

 

Check codes. Still P1000? Then. not good. P1111, then all OK so far. Other codes? Post 'em

 

Don't understand...I need to hope for P1111? What about a problem of the Evap that's under the car that takes fumes from tank?# months ago while dealing with my Fatigue from cancer I just loosened a hose from one of the switches that moves the fumes the stuff to the front. The Fuel would not go into my tank so I did this. But this was 3,000 miles back...could it be the problem after all these miles?

 

Yes it could. P1000 means emission tests not complete. I expect the evap. system is part of the test sequence.

 

I really meant my post (#28). You always want P1111 and nothing else.

 

Go back to my post. No codes, performance unimpaired and limp home set in the message centre = fault isolated to cruise = most likely fault with microswitch or vacuum or wiring. It is not another fault. For some reason Jag engineers made a cruise fault set the message centre alarm to "Limp Home" but did not define any OBD codes. They did design the circuitry to disable the lamp on the cruise switch on the console when the ECM disables cruise operation.

P1000 says the ECM has been reset and a full cycle has not completed. When it completes fault free you get P1111.

If you have limp home from a major fault you will know. Transmission will start out in 3rd and codes, usually many, will be set.

From the Manual:
"The ECM continuously monitors the cruise control switches. If a switch fails closed, on the initial failure the input is treated as a driver command and the system responds accordingly. However, after subsequent disengagement then re-engagement of the system, the input from the failed switch is diagnosed as a fault. On detection of a switch fault, operation of cruise control is inhibited until the fault is corrected."

To test. Disable cruise after clearing codes and the message centre alarm and drive around. My bet is that with cruise off, you will not get the limp home message. Turn cruise on and it will come back - if it does vacuum, microswitch or a more difficult fault (bad switch, wiring fault or corrupted ECM).

My money is on the brake microswitch

 

I did run yesterday without the cruise light on and the Limp home never showed up. I ran fro about a mile with it on and no problem, the turned it off for the rest of the drive. I'll do the same for a few days to see. I'm still open for more input though...many thanks for you guys!

 

No you went over my head. It has already been accepted that the cruise quit because the Limp home showed up. I need to fix why it goes to limp home then it will cure the cruise problem. I mentioned that I've had a problem with my Evap system and just put a band-aid on it by leaving a evap hose under the car loose so as to let the gas tank breath when I put fuel in it. Otherwise I can't get but a little bit of fuel in it. This was done about 3,000 miles back so I doubt that it is the cause.?? A Vacuum hose loose would be more often if not all the time. Now, has this light on the on-off switch on Console ever been into play when the Brake Micro Switch was bad?

 

What is the part # for the Brake switch?

 

Brake switch


1998 JAGUAR XJ8 Brake Light Switch

Do you know if it's actually bad, or just giving this a try?

 

Excuse my ignorance but how does one turn the cruise control on? I see NO master button, just the SET / CANCEL / DECEL buttons. While driving along I press the SET button but nothing happens.

When I scan, I got no codes but 1 pending code, P1111.

 

The button is to the lower left of the shift gate, next to the sport mode button.

 

Ok, thanks. I was looking for heated seat switches there. LOL Didn't know what that button was for. Looks like a timer symbol on it.

 

The symbol is supposed to be a speedometer. Had me fooled when I bought my XK8. This is where having the owners manual is useful. I bought one on ebay, but it can be downloaded from the forum.