I typically drive in Sport mode. When I start out cold, I notice the transmission often launches me from 2nd gear. As if it knows that my driving is very light when the car is still cold! It anticipates I won't really need 1st gear. But not always.

When I was having severe engine troubles due to the bad ECU, the transmission light would also come on. But it didn't enter Limp mode, stuck in one gear, it was still changing gears, but the changes were abrupt. This could be the same Default mode you feel. I'm not familiar with that document, is it a TSB?

Would you do a valve body drop/check-again/reinstall to be sure of your work?

On the other hand an experienced technician would really know what to look for. All those little devices in the valve body have to be set up just right.

Pop off the end cover of the TCM and check the EPROM. It should have BSKK 1623 0527 on it. Although there also should have been a sticker for it. Seems odd the car missed that upgrade.

 

So the document I'm referencing isn't a TSB. It's dated 1996 and I believe is a supplement to the standard transmission workshop manual as it includes details not mentioned in the main transmission workshop manual. Here's the link:

- http://jagrepair.com/images/Training...s/200_1996.pdf

As far as I am aware (according to the main transmission workshop manual and this extra doc) It should technically never start off in first in Normal mode unless you've really floored it from a stop. It's been happening to me when driving it gently after it starts to act up so something is definitely up. In this doc it says a key cycle will clear the default mode and I have experienced that, but I have noticed it will sometimes start acting totally normally again in the same drive cycle.

Removing the valve body is certainly an option. I'm 99.7% confident all was done correctly, but going back will be on the list if the transmission shop dosent find anything out of the ordinary. FWIW, I also replaced the internal harness while I was in there. My original harness was fine/didn't have any broken pins and the new one went in without an issue so I doubt this is the issue.

In terms of the EPROM update, I'll check again, but I'm fairly certain it hasn't been performed. Theres zero mention in the Carfax and the long term second owner who purchased the car in 1997 performed almost all of his own maintenance work so many TSBs never got performed (it had the original BR6EF spark plugs indicating that the TSB with BR7EFs had never been done!) If it had been performed, it might have been done during the first two years it was leased but I don't have any records indicating this. Once I get back to the car, I'll dig deeper into my passenger footwell.

At the moment, I am back home in Texas (The XJ12 lives in California) so in terms of working on it, I'll just be hearing indirectly from the transmission shop once they can see it. Really I just want to make sure the fluid level is finally correct and that its operating within spec. Its a shame since I wish I could drive it a little harder now with its Michelin AS4s and XJR rear sway bar but the transmission just dosent seem to be happy with any sort of spirited driving.

 

G’day Swagger,

Your mention of replacing the auto box internal harness jogged my memory as I had done the same previously.

When I had my trans rebuilt the techs had some problems with the interface between the box and the tranny ECU and it turned out that the new inner harness had slightly smaller pins than the original and it didn’t connect with the plug to the ECU correctly.

It might be worth checking this out.

Cheers,
Jeff.

 

Update:

My dad was able to find time to bring it in to our neighbor's transmission shop. Despite the fluid level registering as high on the dipstick, it was actually about 1/2 quart low. Topped up and so far it sounds like its all good! I'll check for myself once I'm back in California in a few weeks, but it seems like it was just low fluid level! I'll be embarking on a 1000+ mile roadtrip in August so we'll see how it performs. Fingers crossed!