2006 XK8 with 59,100 miles. New Bosch battery in late September 2012. New brake pedal switch in late October 2012. Brake fluid reservoir is full and clean....

My wife has experienced several different issues regarding the ABS and DSC systems this week. I will describe them as best I can since I was not in the car for any of these episodes....

On Monday, she was rounding a curve while applying the brakes at perhaps 45 mph. Here's what happened:
1. She heard a faint "clunk" that sounded as if it came from the engine bay.
2. She felt a slight pulsation in the brake pedal.
3. The ABS light and DSC light illuminated on the dash.
As she continued to drive, she did not hear any additional noises. She also did not feel any additional pulses in the brake pedal. Both the ABS and the DSC lights stayed on until the next drive cycle, when everything was normal again.

On Wednesday, she was driving on a straightaway at perhaps 35 mph when both the ABS and the DSC lights illuminated and stayed on until the next drive cycle, when everything was normal again.

Today, she was rounding a curve while applying the brakes at perhaps 45 mph when she heard the faint "clunk" again and felt the slight pulsation in the brake pedal again. Neither the ABS nor the DSC light illuminated this time.

I have not read any reports similar to what my wife is describing. I know that when only the ABS and DSC lights are playing havoc, the first suspicion is always the battery while the second suspicion is usually re-soldering the two terminal posts inside the ABS module. But in her case there is sometimes a noise as well as a brake pedal pulsation, if only for a second or so....

I'm looking for guidance on where to start. My hope is that someone will recognize this combination of on-again / off-again symptoms and point me in the right direction....

 

In hard cornering, with use of brakes, I have seen my DSC light come. That is just traction control doing its job. To test, you could find a curve to recreate the problem, then turn off traction and put it in sport mode. If it doesn't come on with a repeat run around the turn, you are probably OK.

Brake pulse is just ABS helping out I suspect.

IMHO.

How fast was she taking that corner again and how sharp a turn was it?

 

I have had the same pulsing in a panic stop, just the abs pump. Just recently I had the lights come on braking into a corner. When I got home the AE found a left front sensor problem which may be a connecting cable defect, or just another example of the abs system functioning. I haven't driven it since then to check further.

 

Seems possible there is something wrong here beyond the ABS system. That system may just be confused by what's going on. The clunk is a red flag.

(Ask your wife to be aware of this distinction: ABS/TRAC light coming on just indicates the system found work to do, which is different from the "ABS/TRAC not available" light. Are we talking the "not available" light in all cases?)

Any chance of a loose road wheel or wheel bearing issue? Or maybe severely worn control arm bushing.

 

The late 4.2 model with DSC feels very different from the earlier ABS / TRAC setup on the 4.0 models when cornering at what I consider to be reasonable speeds.

DSC controls ABS, Traction Control and Yaw Control together. It does this in addition to the normal AntiLock and Traction functions by applying individual brakes and reducing engine power without driver input to ensure the vehicle follows the intended direction of travel.

This brake application sometimes feels through the pedal like a brake 'grabbing' with a sound almost like metal to metal contact and is only very brief. My Jaguar Dealer advised that this was normal and gave me another 4.2 to try which behaved in exactly the same way.

I've had the warning light come on regularly with DSC but not had the error light since the battery was replaced. Prior to that when it did come on, it stayed on but cleared at the next restart.

I haven't had the DSC and ABS error lights together............yet!

Graham

 

Jon, your post triggered a memory of mine of a previous member's documented experience with intermittent ABS errors. More importantly, the slight 'clunk' that was heard, was the leading trigger...let me see if I can find it for you.

https://www.jaguarforums.com/forum/s...-sensor-34343/

I thought it had pictures with it, perhaps age lost the linked photos.

His ABS ring wasn't fully seated in one of his hubs, and it would come away from the ABS sensor triggering all kinds of faults due to the lack of a wheel speed sensor signal being present. ring didn't fall out, but its movement flared up from time to time (such as a corner under braking perhaps?) You'd have to pull the rotor to physically examine it, and having a C code to reference would at least tell you which wheel it was happening on, saving you some dirty knuckles and wasted labor to check both. Hope that helps ya.

 

Thanks to all for your input. I forgot to mention that I cleaned all four wheel speed sensors in late September 2012 per Sam's video. I believe that I properly reinstalled all of them. Perhaps one of them is beginning to fail at this point....

I've instructed my wife to keep me posted on the car's behavior throughout this week. If these quirks keep happening, my first step will be to pull all four wheel speed sensors again for a close inspection and perhaps a re-cleaning while I have them off the car....

On the other hand, perhaps this does indeed fall under the "normal behavior" category as Graham's dealer stated. But after owning the car for just over a year now, it does not seem normal to me. My wife states that at no time was she pushing the performance limits of the car in those rounded curves. She is a very conservative driver....

Thanks again for your feedback. If anyone has any additional thoughts or suggestions, please let me know....

 

As has been mentioned the 'not available' message is a fault, not normal.
If you got that and it occurred on cornering it could be the well-known ABS sensor harness wire break.
As Graham said the system reduces engine revs when the traction control operates as well as braking individual wheels.
The loss in power can feel quite spectacular on icy roads.

 

I just thought of another possibility....

A couple of weeks ago I reported that my wife had driven through the worst greasy grime I had ever had to clean off of a car. It took me three car washings over a week-long period to finally get that crap off the paint and visible underside. Perhaps some of it was also slung all over at least one of the wheel speed sensors....

Could this be the issue now? Perhaps I need to remove and scrub all four wheel speed sensors again....

 

Get the wife to do it - her fault, of course.

 

Jon,

I hadn't associated the two incidents but it's certainly possible there's a connection.

When cleaning the Sensors, it's worth checking the Sensor Rotors are clean and intact (item 5 in the 'Front' diagram and item 12 in the 'Rear' diagram):





It's the gap in these toothed rings creates the signal.

Graham

 

Thanks, Graham. I'll attempt to get a good look at the sensor rotors this weekend....

 

Even if the ABS sensor ring got 'goo' on it, that doesn't explain the clunk just before the error occurred. I'm still leaning towards a more mechanical/physical issue.

 

I also wonder about the clunk she described. Until I hear it myself, I can only speculate. Perhaps it was the ABS pump kicking in....

I'll be pulling all four wheel speed sensors later today and taking a good look at the rings and harnesses. If I find anything out of the ordinary, I'll post it here....

 

Update:

I finally got to the car this afternoon after other projects kept me from working on it yesterday. I found something wrong at all four wheel speed sensor locations. Here's the scoop:

1. The left front sensor had one clogged-up hole (out of four holes total). I cleaned it out with the end of a paper clip.

2. The right front sensor also had one clogged-up hole. My trusty paper clip again did the trick.

3. The left rear sensor harness rubber boot was split open less than an inch down from where the sensor plugs into it. I could bend the rubber boot back, open the split, and see the two wires inside it. I cleaned the rubber boot as best I could and wrapped it with two layers of electrical tape.

4. The right rear sensor harness rubber boot was also split open in the exact same place. I did the same electrical tape repair to it.

After re-installing all four sensors and wheels, I took the car out for a ten-mile test drive. My speeds ranged from 25 mph to 75 mph and I got into some curves fairly fast while quickly applying the brakes. No clunking noises, no warning lights or messages on the dash, no ABS pulsations felt in the brake pedal, no issues at all. The car behaved normally....

Back on the subject of both rear sensor harness boots being split open, I used my hand to follow the harness wires underneath the car as far as I could but I eventually lost their track. Where do these harnesses terminate, how long are they, and what is involved in replacing them? Do they plug into another electrical connection somewhere in the trunk or perhaps behind the back seat? If so, how do I get there?

I know that wrapping the rear sensor harness split rubber boots with electrical tape is not a permanent fix. Is there a more permanent way to seal up the splits in the rubber boots, or is replacing the harnesses with new ones the only viable solution?

 

Anyone familiar with these rear wheel speed sensor harnesses? Can you answer the questions in my post above? Thanks for any assistance you can provide....

 

I can't help with the harness but you could fill the boot with neutral cure silicone - NOT the sort that smells of vinegar.

 

Steve,

Any ideas where "neutral cure silicone" can be purchased? Never heard of it....

 

It's very common now.
Exterior Siding/Trim neutral cure silicone,10.2 oz,Clear - RT Sales
I'd guess you'd get it in any plumbers in the US.
It is non corrosive when it cures - ideal for 'potting' electrical stuff.
Obviously clean the boot and dry it with a hair dryer beforehand.

 

Update:

I was out running errands in my wife's XK8 this afternoon. Did about 25 miles with no issues or warning lights on the dash. But I'm not convinced the problem is fixed....

I'll be doing the car's 60,000-mile regular service in about another 1,000 miles. While I have the wheels off the car to rotate them during that service, here's my comprehensive plan for trying to fix the intermittent ABS/DSC warning light issues going forward:

1. Seal up the two rear wheel speed sensor harness rubber boots that are split using the RTV "neutral cure" silicone product recommended by Steve above. I'll try to really build up multiple layers completely around those splits in the boots in an effort to keep any moisture out for years to come.

2. Cut the factory plastic tie-straps that secure the two front wheel speed sensor harnesses to the front wheels, wiggle them around to create more slack, then re-secure them once they are definitely looser. When they are factory-tight like they are now, too much stress appears to be placed on them via hard steering and the electrical connectors can apparently pull apart just barely enough to throw the dash warning lights.

3. Disconnect the electrical connectors between the harnesses and the wheel speed sensors, spray the connectors liberally with contact cleaner, let them dry out, then firmly re-connect them once they are sparkling clean.

4. Spray all four of the toothed cog rings (the part that the sensors read when the car is in motion) with brake parts cleaner in an effort to remove all grime and potentially magnetic brake dust residue that may be confusing the wheel speed sensors, causing false readings and then throwing the dash warning lights.

5. Scrub the wheel speed sensors again with a toothbrush and dish soap as I initially did in late September 2012 when I first attempted to chase down these dash warning lights. Make certain that all four small holes on each sensor are clear and not plugged up with debris.


After I'm done with all of these tasks, I should have the cleanest wheel speed sensor system on the planet. I hope that resolves the intermittent ABS/DSC warnings my wife has been receiving during the past week or so. I would not be surprised if these steps need to be added to the routine maintenance required by her XK8 at every oil & filter change / tire rotation (which I do at 6,000-mile intervals)....

If anyone has any additional suggestions or experiences regarding fixing this pesky issue, please chime in here....