Hi everybody,
I am encountering a cold start issue on my 1997 Jaguar XJ8 3.2 V8: sometimes the "Gearbox Fault" message appears when trying to shift from P to D (D light doesn't stay on, flickers briefly if I jiggle the lever). Other gears (R, N, P) engage fine with lights on. After warming up, everything works perfectly—no faults, all gears shift smoothly.

A short while ago, I went down to the garage to film a short video to attach to this post and, as is often the case, the problem didn’t occur as usual; instead, the fault happened the first time I changed gear (from P to R).

No codes read yet (need OBD scanner), but symptoms point to J-Gate microswitch or shifter contacts per other threads.

Any advice on DIY fix, part numbers for the switch (LJA6190AC?), or common causes?

Located in Rome, Italy—local specialists welcome too. Thanks!

 

You might want to check your ATF (Automatic transmission Fluid) level.
I think it needs to be done with the engine running: Car safely secured on stands, engine running, opening the check plug and the ATF should just drip out a bit.
If it's too low, you might want to do a complete ATF flush:
https://www.jaguarforums.com/forum/x...-flush-265900/

 

Just don't use atf, lt71141 goes there

 

On my 2003 XJR (that I don't have anymore) the transmission would act weird at times. I had to adjust the shifter cable under the center console shifter assembly a but to get it to work. I think it was not contacting the little microswitch correctly that is part of the shifter assembly.

Also, I used to get GEARBOX FAILED warnings on my first 2000 VDP. After changing everything, (including the transmission and throttle body) it turned out to be a faulty connector on the throttle body pedal position sensor. Not the actual throttle position sensor. Of course the throttle body on your car would be different. All that to say sometimes it's not an actual failure but some other problem causing the failure.

Lastly, I'd certainly check the fluid level in the gearbox. It's a rather involved procedure though. No dipstick..

 

> Just don't use atf, lt71141 goes there

???
Yes, LT71141 goes into THAT gearbox - LT71141 IS AN ATF! ATF (as I wrote in brackets above) stands for Automatic Transmission Fluid.
My attached link above - containing all the details - also specifies LT71141.

 

If you don't specify the type of fluid most will happily drop red atf there and call the day, to avoid mistakes we call this stuff by its name

 

Hey Eduardo,

Yes, it may be a fluid issue, as you suggest that, once warm, it drives well.
However, I recommend you do some initial checks . . .

It is also possible that you are correct that it may be either a shift cable or Park microswitch issue.
Why? Because that blinking Park light (on - off - on - off) is an electrical switch issue . . . not a fluid level issue.

Suggest you read my thread in this X308 forum "Rare XJ8 Sport with broken gearbox . . . or was it?"
<https://www.jaguarforums.com/forum/x...earbox-246896/>

Several pics of switch layout and advice . . . vital for me as workshop manual either misleading or wrong for my vehicle.
First, check that auto end of the shift cable is fixed firmly
Then, adjust by small increments, the locking nuts either side of selector end to engage the P position precisely.
Finally, treat R&R of selector (to get at microswitches) with care, as it's easy to damage the switch blades.

Note that most likely fail is dislodgement or breakage of the tiny SS blade of the Park microswitch.
If so you don't need the entire switch, wiring and connector . . .
Just buy a generic switch that has same lever blade and swap it in.

You may still need to address fluid level, but my advice is do these things first.

Cheers and best wishes,

 

Thank you so much for the suggestion, Peter.

I’ll probably follow the detailed instructions you provided in your post.

I really appreciate your help. I just have one question: what kind of pump did you use to fill the transmission with ATF? Could you perhaps suggest a link where I can buy a similar pump? My trusted mechanic, a dear friend, doesn’t usually work on automatic transmissions and told me that a very expensive pump is probably needed for that job.

Thank you so much for your help, David. I also think that before changing the oil, I could try a more cost-effective solution by checking for a loose connection or something similar inside the transmission housing—though I’m not sure, even with my mechanic friend’s help, that I’ll be able to tackle it myself. I’ll try to take advantage of the advice other users have given in the posts they suggested I read. However, my situation may differ slightly from others in that these two factors are present:
once the car is warm (about 10 minutes after starting it), the problem no longer seems to occur;
the problem occurs almost exclusively when shifting into D; it’s the gear that the transmission most often struggles to “read,” and consequently, the corresponding warning light doesn’t come on.

Thank you for your support.



Thank you so much for the suggestion; I’ll try to make the most of the photos you took of the components and the instructions you recommended.

I’ll keep you updated.