Hi, I had this problem earlier this week, I was quoted 1000+ by the main dealer over the phone before he had even looked at the car.
What I did was remove the wheels and the ABS sensor is easily located, it has a 2 pin plug connecting it to the lectrics, disconnect it, get a multi meter and test the resistence of the sensor, it should be around 650 ohms, the lowest I had was 615 ohms and the highest was 658 ohms except for the one that was open circuit!
A new one from Jaguar is 147.95, a used one from my local Jaguar specialist was 20.
Apart from struggling a bit to get the old one out, it's was easy enough to replace.
Wednesday, December 19th, 2007 AT 10:15 AM