When I apply my brakes either the brake light or anti-lock light or both come on.

I've had the car for about 2 weeks and doing the brakes are on my to do list, but the system appears to be working (i.e. it stops the car smoothly without any noise).

Fluid level is at the correct level.

Nothing out of the ordinary about brake pedal operation.

So why are the lights coming on?

 

Likely that the brake accumulator vessel in not holding pressure, so the pump must activate every time you hit the brakes. The clicking you hear under the dash is the ABS pump motor relay activating on every application, which it shouldn't need to be doing.

 

JagTechOhio,

Would cleaning the ABS sensors improve the Anti-Lock light issue? If I remember correctly, you need an 8mm socket to remove them. Also, what would recommend as a cleaner?

Mike

 

No, that is completely unrelated to the issue he is having on this model. The pressure switch is activating the warnings when he steps on the brake pedal, either because the switch is bad (less likely) or because the accumulator vessel is not maintaining reserve pressure (more likely).

An ABS sensor fault on XJ40 will cause the ECU to fail the self-test and illuminate the warning, but it will be constant in most cases. Such a fault will not illuminate the brake warning light, just the anilock light. If Mr. Puppy presses his VCM button at the same time he applies his brakes, the word "Fail" will appear instead of his odometer mileage. That's fail because the brake boost pressure is low, and in that case the ABS will not have the requisite reserve pressure to function properly either.

I read about cleaning ABS sensors on all models constantly, and wonder what I've been missing. I think it's much more likely that people who go through the procedure are unknowingly improving bad connection problems, or getting lucky when they manouver the harnesses which are the real culprit. I've seen sensors covered in grease from failed seals, metal filings from torn up rotors, and corrosion from Ohio salt: the sensors all still worked fine, unless they were failed sensors. You can clean them with Brakleen, Electronic cleaner, MAFS cleaner, or whatever you got.

 

JagTechOhio,

You are absolutely correct; I do get "fail" when I push the VCM button.

When you refer to the accumulator, is that what is typically called the brake booster on most cars or is it something in addition to the brake booster?

Thanks

 

I only work on Jaguars, so I don't have a basis for comparison as to what is used on most cars. When compared to a common vacuum operated brake assist booster, the system on your car is a completely unrelated animal. You need a good manual with a system operating description before you attempt to troubleshoot and repair your brakes.

 

Where are the ABS sensors how do u og about replacing them?