So, I got an 03 XJ8 two weeks ago, 60k miles.
When I got it, the ABS light was on, and it showed ASC Fail/TCS Fail on the display. The 'Trac Off' button did nothing (light did not illuminate when pressed). I accepted this, as I've never been a fan of ABS or TCS systems anyway, and argued my way into a good price cut for it. The Check Engine light was not on.
I've driven about 200 miles so far, and loved every second of it (my first jag - always a dream of mine to have one). Yesterday, however, I encountered something strange...I hopped in to drive home from work (back roads), and at one point I had to brake hard and noticed the ABS kick in for the first time. I hadn't noticed, but all of the warnings were gone and the lights were off. The Trac Off button worked now. Accepting this as a fluke, I continued on with my newly working systems. At night, when I got back in to go to dinner, the lights and warnings were back.
Today, I was driving in to work, took the highway this time. ABS Light and warnings were still there. About 6-7 miles in, the check engine light came on, and the ABS light was still on but the TCS/ASC Fail warnings were gone, and my trac off button worked. I have gone out and started it a couple times, and it remains in this situation.
I am stopping by autozone on the way home to get the codes pulled - but this sounds entirely too strange, like the diagnostics systems are freaking out randomly...Has anyone ever seen anything like this?
Thanks.

 

Update...got the codes, P0128 and P1000
P0128 is engine not reaching operating temperature/thermostat stuck open. I've never had an issue with the car warming up, it's always right up to normal operating temp quickly...if it's a few degrees short, it's not noticable. However P1000 means drive cycle not complete - could explain the weird diagnostic issues, but after 200+ miles, shouldn't I be alright?
Also, my ABS worked fine on the way to autozone, and was off when I left...

 

pilot, based on what you are describing, I would be venturing to guess that your engine coolant temp sensor (ECTS) is acting up and has failed, making the computer think that the coolant system is cold. But, due to this, the computer is looking at other sensors and figuring out a viable temp indication from another sensor to substitute in.

What I would tell you to do is to get your hands on one of the infrared thermometers and check the temperature at the point where the coolant enters the radiator or where it leaves the motor (whichever is easier to get to). It should be reading in the neighborhood of 180F. If you are down around 150F, it could be that your thermostat is truely stuck open. Sounds like the rest of the system is functioning properly as it relates to the coolant system.

As for the ABS system, it could be a number of things causing what you are seeing. Because the speedometer is pulled off of the 4 ABS sensors and these signals are also used for activating the ABS system and the traction control system, it is very possible that if one of the sensors had some gunk on it from not being driven or one of the wires was sitting funny, it would cause your lights to come on. If a sensor fails, it will cause the ABS not to engage but your speedo will still work as it will look at the other wheels and ignore the one it thinks is bad.

Hopefully this gets you back on the road with no lights on.

 

Thanks. reply:

1. Hrm, what other sensor would it get a temp reading from to transmit to the gauge? I'm guessing it may be the thermostat...though with it wide open, I'm amazed it heats up as fast as it does with this horrid cold front coming through this week (35-40 deg in october!)
Though an IR thermometer would be a nice thing to have, I'll have to pick one up.

2. Is there any documentation on working with the sensors? like, a voltage I could test at standstill to find out which one is broken, where they actually are mounted, etc. I'm perfectly comfortable working on brakes and such but have never owned a car with ABS before and so I'm new to the sensor bit...every car I've had was just a single speed sensor where the trans meets the driveshaft, easy to get to under the car, and obvious when it had a problem.

3. With that P1000 code...I won't be able to pass inspection with that, which is due Nov 30...Am I missing something on completing this 'drive cycle'?

 

arada, I am attempting to locate more information, but unfortunately my JTIS is a little FUBAR'ed at the moment and isn't playing nice. I will see what I can find. Some times the computer will also look at things like the cylinder head temperature or something silly like that and figure out engine temp. I will see what I can find and pass on the info to you. I would say to get on E-bay and spend the $10 or so on your own JTIS CD. I think you will find it very informative and will also help you get into aspects of your car that you don't normally play with. For example, if I remember right, if you get 3 different resistors (100 ohm, 180 ohm, and 260 ohm), that will exercise the temp gauge between the low, mid, and high points. I know those resistances are good for the fuel tank level gauge.

Something else you may want to consider is simply disconnecting the battery from the car for a few minutes and then reconnecting. Sometimes this will make the computer relearn things and solve silly problems like this. Just keep in mind that you will more than likely end up having to insert a code into the radio to make it work again and reprogram the windows. may be a few other things based on options associated with your car. But, normally redoing those takes but a few minutes.

 

ha, damn, a code? where would I find such a code?
I miss the days when the worst problem was resetting your clock and radio stations...

 

replace the thermostat, its bypassing coolant and is partially sticking open, its never been a sensor.

 

Alright, latest update. I checked the coolant again and noticed it had gone down slightly from where it had been and so I topped it off...but there was no sign of coolant in the oil or smell of it in the exhaust (thank god). Then I decided to let the car idle and see how well it warmed up, as the issue here seems to be that it is underheating...better than the alternative, I suppose.
So, as soon as it starts to heat up, sitting in my driveway...a little stream of coolant-smelling white smoke starts seeping out from under the hood. Wouldnt've been noticable when driving, but standing still for a while it built up. Popped it, it was coming from behind the engine on the driver's side, right under the coolant reservoir. Turned it off and got a flashlight, and noticed some wet spots on the wire insulation right between the tank and the exhaust. There was no noticeable drippage, but I felt around and found a little damp drip down the side of the reservoir under the covering, right at the seam of it. Looks like it was slowly leaking down and burning off when it hit the hot exhaust.
I let it sit and cool, checked the coolant the next day and it was down to the level I had noticed it at before, and no longer had any signs of dripping (the level had dropped below the leak, it seems). So, a minor external coolant leak, that's something I can fix.
My question remains, though. How would a tiny coolant leak throw the code for a stuck-open thermostat? Wouldn't that, if anything, deprive the system of coolant? It still runs cool. And I'm sure in a vehicle with so many possible notifications, there would be an error showing for low coolant...if what was in there after it dripped some out was not enough.