I recently took my 2008 Ford Expedition in to be serviced because the ABS light was on. I was told that the left front wheel speed sensor needed to be replaced. As they go to do the repair then the wheel hub needed to be replaced. After ordering the part and the work was started I was then told that now the right wheel speed sensor needed to be replaced. Should the initial computer diagnostic system picked up that both needed to be replaced instead after the work was started?
Sometimes not, depending on how it failed. The ABS computer watches and compares all four sensors while you're driving. When one fails, there is nothing else to compare it to. It can't rely on the rear sensors because it knows they will be going at different speeds when you go around a corner. Once the first sensor is replaced, the computer will be able to detect the other sensor is not working. The mechanic has no way of knowing that until the first one is replaced. I'm not sure which type of sensor Ford is using but if it is built into the wheel bearing assembly, GM has been using that design and they are having a huge problem with the signals dropping out from the tiny normal play that develops in them. Their junk metal bins are full of those bearing assemblies. Funny thing is those bearings would work perfectly fine on cars without anti-lock brakes. To make it worse, the same exact bearing without the sensor costs almost twice as much as the bearing with the sensor.
March, 17, 2011 AT 1:39 AM
Hey Caradiodoc, yep Ford is using same style, and my junk bin is full of them.