Hei, next problem. When I bougth Jaguar XJ8 4,0 2001MY, brakes are vibrating when press brake pedal. ASC and Traction failure was active- no signal from front right sensor. I repair wiring and this problem is gone. But after that starts very wierd problem. Almost every time I brake, ABS start to work on front left wheel. No diagnostic trouble codes on ABS and Traction control. If I switch off Traction Control problem still active. I connect computer and drive- all wheel speed sensors working correctly. Where is problem?

 

Your problem is either pads, caliper or rotor for that wheel. I am guessing that the wheel seems to lock or pull when braking. The manner in which ABS works it is doubtful you could feel the action at one wheel.
Visually inspect and see if you have a defective brake pad where the friction material is gone.
Rotate the rotor and see if it seems to wobble back and forth. (warped rotor)
Have someone press on the brake pedal and observe that the caliper releases when the pressure is removed. (frozen caliper)
Try that and let us know what the results are.

 

Sorry, I forgot to say that I replace discs and bads today. Check calipers too and they are ok. And I now how it feels when ABS is working. I work everyday in SAAB service. You can feel it in pedal.

 

ABS will only activate if one wheel or more starts to skid (turn more slowly than the others). How do you explain that one wheel skids every time you apply the brakes? How do you know it's the front left wheel?

 

I can´t explaine , I just feel it and hear too... And this happens not every time but maybe 8 of 10 times.

 

I think that the sensor on your left front wheel is also faulty, but in a different way, one that doesn't trigger a fault. It is losing the signal when you pass below a certain speed, which the ABS interprets as a locked wheel. However, no error is triggered as the signal is OK at higher speed, when the system checks that the ABS is working.

This is possible when the signal is weak. At higher speeds, the inductive pulse is stronger than at low speeds. If the sensor is faulty, particularly dirty, or the wiring has an issue, the signal might be too weak at low speeds to register.

I had exactly this problem on my XJS. Braking was excellent until you dropped below 30mph, when it would suddenly trigger the ABS and veer violently to the left. Quite entertaining. All I had to do to fix it was remove the layer of grease and dirt that had built up on the sensor.

On my 2001 XJ8, I had issues with a bad connection at the inline connectors, just inside the engine compartment. Follow the wires from the sensors and you'll find them.

I would clean and add dielectric grease to the connectors on both sides, and clean the ABS sensors and rings on both sides too. Is there an adjustment between the sensor and ring?

 

Hi again. I check all sensors and clean sensors and connectors. Still nothing.
All sensors showing same speed. Wierd thing is that when computer is connected and I drive brake works normally. When I disconnect computer ABS starts again. No codes in ABS or Traction control. I switch off Traction but still same thing. And no matter what speed is- low or high.