Hi, i'm new to the forum but not new to Jaguars, I have had many over the last 25 years and for the last few months my second XK8 1998 ran fine until 2 days ago.
The aforementioned 5 amp fuse blows the instant ignition is turned on. I now get spurious message saying engine failsafe mode, Trac and ASC not available, Gearbox Fault, etc etc. and the driver's blower motor comes on, even with the control panel unplugged! I stopped that by unplugging the little sensor on the underside of the lower dash on the driver's side. I plugged in my code reader but, of course, there were no codes to read. I have removed almost every relay and module but no change. I even disconnected the Inertia Switch....just in case and checked the display whilst it was still unplugged and,curiously, I then got additional messages displayed which never showed before. They were- Low Washer Fluid and Passenger Door Open....which it was but this has never appeared before, also Suspension Fault and Electrical Fault. I'm running out of ideas where to go next.
There was a thread in late 2018 which seemed to be going in the same direction, in that the same fuse was blowing, but it suddenly stopped before revealing the outcome of the investigation!!!! It was like reading a gripping book and when you turn the last page it's been ripped out! Any ideas?
Any ideas would be much appreciated. I will carry on tomorrow removing whatever is left to remove...after that i'm stuffed

 

Welcome to the forums Maurice,

I've copied the question from you Intro for advice from members with the same model.

Graham

 

Jaguar Electrical Guide 1998 XK (S98) shows NO Fuse 10 in the EMS fusebox. (5 inside a square)

I looked at more diagrams and found (circle 5E) #10 5 amp EMS fusebox.

Look at figure 4.2 4.3 4.4 4.5 4.6 AJ26 ROW Engine Management: Part 1 and 2

Figure 1.5 shows the fuse goes to Engine Management (circle E) 39,40,42,43 White/Red wire.
The figure 1.5 also shows 41 to go to figure 5.1 (gearbox normally aspirated)

It powers things like the ECM, vacuum switching valves, and the gearbox rotary switch.

 

Progress! Typically the last module I disconnected was the Transmission Control unit and the fault disappeared!!! The voltage on F10 in the EMS fusebox had been 12.9 at which the fuse always blew. With the Trans. module unplugged it dropped to 10.2 and doesn't blow and I can start the engine and it runs fine. ( have'nt check the amperage yet) Luckily I have a lot of spare parts and amongst them I found another Trans. Controller, fitted it but same result so next to check is the Rotary switch...fingers crossed that's the culpriit but I don't have a spare one of them but I might borrow the one from my XJ8 just to prove the fault.

 

HI, thanks for the info. I unplugged the rotary switch and the fuse didn't blow when I turned the ignition on. I will check later this evening to see if the rotary switch on my V reg xj8 is the same so I can use it to prove/disprove the rotary switch being the real cause of the fault.

 

Joy of Joys! I dived under my XJ8, whipped out the Rotary Switch, well I say whipped it out but I had to jack the front end of the XJ8 high enough to get under it to unbolt the switch in a very narrow space, then wrestle with the plug end then un-clip the cable from 2 retaining clips on the gearbox so it was about 2 hours in total. Then the same thing on my XK8 so that was another 2 hours including fitting the replacement switch but finally I turned on the ignition and all is well, so, it was the Rotary Switch causing all the problems and, like I said, it was the LAST thing I checked!!! But at least I now have a comprehensive knowledge of all the secret places Jaguar hide relays, connectors, sensors,modules etc etc. on the XK8 I think the strangest thing to happen was when I disconnected the Inertia switch and when I turned on the ignition I got a whole lot of other messages which I mentioned already...anybody got any ideas why that would be?