I picked up a 2000 X200 3.0 V6 SE auto in September. It had an issue with the traction light constantly flashing. I took it to a grage and they diagnosed a front wheel sensor, which they replaced and it went away. A short time after I had the front discs and pads replaced, and the fault came back, but this time I had the flashing traction light sometimes and a constant traction light at others. It seemed to flick between them with each successive engine start. I took it another garage, and they did a calibration on a steering wheel sensor, and the car was fine for a week or so. Then one day I was driving along and I got "DSC SYSTEM OFF" followed a few second later by "DSC SYSTEM FAULT". I took it back to the second garage and they cleared some codes and it was again ok for a while, but then the "DSC SYSTEM OFF">"DSC SYSTEM FAULT" happened a few times so I took it back. They said that it looked like the ABS unit could have a fault, and that the best thing to do would be to send it away to a specialist for a repair. I decided not to proceed at that time as there were a bunch of other things the car needed, and I had a really good run from that point where I didn't get any fault lights for a few hundred miles. Then last week the "DSC SYSTEM OFF">"DSC SYSTEM FAULT" happened while I was driving, and it's been showing "DSC SYSTEM FAULT" ever since.

If when starting the car the light is out and stays out until you touch the brake peddle. the problem may be you need a brake servo.

 the issue is the solenoids that sit on the front face of the servo has gone down. they say that you cannot buy them separate from the servo although they just screw into the servo. cost of new servo £449.00 + vat. you may have issues with the ABS system on early models  this also may require changing and would need pairing together after fitting. Jaguar have the diagnostic equipment to establish this, normal garages may not have this capability. cost around £40-50. If light is on permanently same applies.