Figured I'd built a bit of faith in the Jag with recent repairs so I went and took it on a 60 mile each way trip I needed to make today. Right as I headed out and got on the highway, revs went up for merging and then wouldn't go back down after letting off the throttle. This was starting out stone cold, maybe a half mile of neighborhood roads then getting right on the highway. RPM was at 3200ish when going around 55-60mph, I don't remember exactly. I tried various things to encourage it to shift in either way, varying throttle input, switching in and out of sport mode (I always drive with Sport on), sweeping the J gate, etc. Everything but shifting in and out of neutral... Since this trip was time-critical I turned home and parked the XJR and took another car. On the slower roads home the transmission almost felt like it was in limp mode, it was still stuck in that same gear it was in before. When I got to my driveway I tried reversing and drive again just to make sure it somewhat worked, but only to move forward/back a few feet. There was no error codes at all on the dash, which was the strangest part to me.

Came back to it later, drove a few miles to the local grocery store and back, no issue at all. The shifting has been a bit clunky so I have had a fluid/filter change on the list for a bit, but it felt like it has when I drove it to the grocery store. I tried the J gate and shifting up to a higher gear had a very long delay, maybe a couple seconds, while shifting down was pretty fast(this was also with the transmission fairly cold). There's a bit of a clunk downshifting, but I'm going to assume it's worn suspension/subframe components until I do those and trans fluid and find otherwise.

For a bit of history, I posted a while back about a persistent P1797 code with no symptoms (see https://www.jaguarforums.com/forum/x...mptoms-176735/) and the suggestions were replacing the electrical coupler along with the fluid/filter. Then life happens and I've not been able to get it yet. I did check fluid levels around that time and found the fluid was rather low, with the trans warm the fluid barely touched the dipstick. I bought a liter of Pentosin atf1 LV and using all the proper fill procedures, topped off the trans until fluid measured to about 2/3 between the 25C and 80C marks. At the time my thermometer measured the pan at 60C, I was worried about overfilling so I let it be there.

So... what the hell? Could it just be trans fluid being old? I'll try and crawl around and get at that connector to take a look if I get the time, it seems like there's exhaust nearby to make it difficult to access. And to think I was ready to buy a press and tools for the front end, guess those will get pushed back by trans parts...

 

What color was the fluid when you checked it? It sounds like a dirty filter, hopefully its that simple, but now you have symptoms for that prior 1797.

 

You need to check the TCM for DTCs. The ECM might have logged a fault but the TCM will tell more of a story than just the engine 'referring' to a gearbox fault.

bob

 

It's a sort of dark yellow/grey, hard to describe. The Pentosin stuff that went in was the expected bright red. It seems really strange to have the limp mode happen without "gearbox fault" or anything popping up on the dash, and the P1797 has two separate causes listed, only one of which causes a limp mode...

In any case, I ordered a kit of parts for the trans: 8 things of shell atf 134, gasket, filter, plug+seal, and electrical connector. Hopefully that comes in on a day that it's not raining and I'm free to do the fluid change, and if I'm really lucky that's enough atf for two drain/fills, or I could use the torque converter plug if mine has it.

EDIT: just saw your post bob, would that need higher level tools than my OBDII scanner? There's a nearby indy that says they work on Jaguars, I've been meaning to call them and pick their brain, maybe they have dealer tools.

 

I'm not for sure, motorcarman should be able to verify, but I believe your trans is a Merc like my 2000. So if you know a Merc Tech, that should help.

 

I think in theory the elm327 could read the TCM - but no-one's written the software, so yes a dealer-type tool (IDS/SDD, WDS, maybe AutoEnginuity and some others).

Each of the modules can have codes inside but OBD is only about emissions so can't pick them up unfortunately. The car makers tend to refuse to open up the way to DIY this stuff