Hi Jaguar Enthusiasts, i bought my Jag xj8 (build 1998) in the UK 2009. I love it, but the MOT (in Germany TUV) stopped her Driving Life for 4 Years. A lot of rust and some holes in the Car Body we have to fix.

Now it is fixed, but she doesn't want to start. My Mechanic Friend didn't work on the electric (because that is ok). He only fixed the Rust Problems, plus Breaks and put some underbody Protection. In January 2024
we make a test Start and she starts and runs well. But than he fix the Rest of her Rust Problems (Metal holder of the Front and Rear Bumper) and finish the Underbody Protection.

Then we put a new Battery in and try to start, but she can't. She shows on the Display Electric Fault, Suspension Fault, Failsafe Engine Mode and incorrect part fitted and also the remote Key cant open the Car. With the
normal Key, i can open the Driver's door and the Alarm stops. That's it. My Friend and I are not really good in Electric. So we take her to a garage on a Trailer, but they check the Main Control Unit and every Relay, and we make a Hard Reset but nothing happened. We connected a long Cable from the Battery Negative to the Front Engine and only the "Gearbox Fault" is on. But how can we find the Ground Cable or mass Problem. My Garage is not really a
Jaguar specialist and i talk to a Jaguar Technic man in a Jaguar garage in Hamburg, but they all have no idea. Because in Germany I think we have not enough People with JAGUAR Experience so I ask here on this Forum for Help. Dorothy, That is the Name of my Jag was nearly 15 Years (minus the 4 Years of standing in the Garage for Repair) my second Love (after my Wife :_))) and I want to use her. Also because my Friend who repaired all the rust Problems and me are looking forward to see Dorothy on the Street again. She is dark red and pretty. And she is English. I am born in London but over 60 years in Germany so sorry for my English.




Greetings Barry . .

 

Nice Jag.
There is no place like home! (That's what Dorothy says in the Wizard of Oz... Maybe that's why she does not wanna start and leave home...
I understood all you wrote there in English - but you added an involuntary joke there...:
> ... my second Love (after my Wife :_))) and I want to use her.
...because in that context "use" has a completely different meaning...
I am from Germany, too, but I live in Australia, and thus I understand the finer nuances of the language...

OK, about your problem:
You are relying on the error messages on the display... Don't do that. The display will tell you anything. If there is an error message on the display, you know that something "may be" wrong, but you do not know, what it is. I have the permanent annoying message that my rear bulb is blown...: No, it's not, I just use LEDs...

At another occasion I forgot to put the connector back onto the throttle control motor, and I had all kinds of "love letters" (messages) on the display, like: ABS failure, and lots more, and all those messages were wrong.

You need a OBDII code reader. you can find them online, and even dirt cheap (AUD$ 10 - 15), and those do work AT TIMES real good, but occasionally they fail to communicate an occasional error to you, hence I'd recommend to spend a bit more...

You did already make an important discovery, when you connected the battery-minus with a starter cable to the engine block to the effect that some error messages disappeared. So yes, it really looks like you forgot to reconnect a ground cable - or did not connect it properly.

Maybe this helps (XK8 and XJ8 should be fairly similar in this regard):
JagRepair.com - Jaguar Repair Information Resource

AND: As I already mentioned above (something I did wrong): Check again, if you reconnected each and every connector, which you disconnected before.
And something I always do, before reconnection a connector: I spray it with CRC 2.26 (electric contact spray).

Gruesse an den Michel und lass Dir ein Matjes-Broetchen vom Fischmarkt schmecken!

 

It is my understanding there could be many electrical issues with these ladies if
major welding is done without the battery being disconnected. It might be wise
to search for postings where major welding was done to see if you could gain
some insight into the particulars.

 

Somewhere you have a missing connection, as noted, most likely a ground.

See if the attached helps. Also, on this forum you will find a wiring diagram.

 

On the power side there is a easy test to ensure power is distributed to all points of car

Have key in run but not started , remove the 4 relays that I will post after research and thee relays should click in your finger tip back to open

A relay can click getting the correct command but still be bad relay intenally ( power contacts inside comprimised ) so there are swapping options of the same part #

ECM control relay is one , ignition positive #1 relay engine comportment fuse box . ignition positive # 2 located left heelboard fuse box , Trunk fuse box relay ( never mind ) , Auxillary relay right heelboard fuse box

This can be seen on page 31 of your wiring guide linked below

X300 98/E COVER

This test also verifies the ignition switch and if at fault the Ig switch removes from key barrel so no new key needed




Research and editing done , ask questions

 

There was someone recently that did some welding on a X300 or very simular X308 that gave him a spot of stumble under his bonnet

There are the points of the car as the false bulkhead in the engine compartment and the nuts on the bus protection module ( mega fuses can be blown) and their large battery cable terminal nuts on the module , contributers have good pics

Battery condition and never install battery in backwards , positive post car fwd ...............ask me how I know . recoverable

 

Adding to the comments above: IF a relay is your problem, the problem with that relay is most likely that the contacts inside of that relay are oxidised, i.e. when they touch, they do no longer produce an electrical contact. Most relays can be opened up and then you can visually inspect those contacts, and if required clean them (in really bad cases with very fine sandpaper).

I have never welded anything on a Jaguar, but - as mentioned above - I hope you had the battery disconnected, when you did.