Hello,
My current project is working on my son's 1999 XJ8 and getting everything fixed for my grandson as he just turned 18 and is in process of getting his drivers license. Most everything else is resolved but the last major problem is the power steering is not acting right. It makes no difference what speed you are driving; the level of power assistance does not change.
I started by changing the power steering pump but that had no effect on the problem so I have been looking into the electronics of the PS assistance circuits. It appears that the level of steering assistance is electronically adjusted according to the speed of the vehicle; which I'd imagine is maximum assistance at stop and gradually lessoning as the speed increases. On the instrument cluster there is a "Vehicle Speed" output (FC25-6) that goes to the speed control module which is located under the front bumper left. (See attached) (This control module has also been swapped but it did not resolve the problem). I'd assume the actual speed information is coming across the CAN buss from the ABS module to the instrument cluster and in turn provides the output signal to the PS control module that is connected the steering rack. At the point I have not replaced the rack but before doing that was thinking of putting a meter on the speed line (Instrument Cluster FC25-6) and watching it while I drive the car to see if it changes before I do that. (I did check the 10A fuse, F14, in the left heel box which was good so it's getting power)
So my question to the group, has anyone else experienced this problem? If so, was it the a failure in the instrument cluster, the ABS unit or the steering rack? Or something else that I'm overlooking?
Thanks much, Dave Warner

 

Where the lower steering shaft meets the rack, just to the left of where it couples at is a servo. Make sure it’s clean inside the connector and of course plugged in.

 

Well, I returned from my trip so got back to working on the 1999 Jag steering problem. I plugged my meter into the instrument cluster FC25, pin 6 where the steering control unit signal originates. When stationary it read about 13v and as I increased the vehicle speed it went down to 7.2 v and may have gone down further but I only drove the car about 200 yards; enough to know the circuitry was working. I could find the wiring diagram of Power Steering Assistance Control Module on FIG 11.1 of the 1999 schematics but it did not show in the pages of the module location diagrams so searched the internet and found a picture of its location; behind the driver side front kick panel! (In the original post, I said it was located behind the front bumper; that is the fan control module) I took a module from one of my other cars and plugged it in and the steering works perfectly! I have ordered one from ebay and once installed that item of the 1999 Jag fixup will be complete. I have repaired many problems with this car.....I may post all the problems and resolutions in a later post.
Thanks for the replies Jaguar friends.... This forum has been extremely helpful over the years and I am happy to contribute....best, Dave