OK - I've done research ~ad nauseum~ but still need some info. 2003 XK8 with only 18,000 miles. My issue was the fairly severe bump from 2nd to first gear when coming to a stop - sometimes a full stop and sometimes a "rolling" stop, and then accelerating lightly. Feels like someone "kissed" the rear bumper when stopping. From the research I've done, I figured with the age of the car, the trans could probably use a refill and replacement seals.

Yesterday, a friend and I drained the fluid; fluid was very clean, as were the pan and Mechatronics unit. We replaced the connector sleeve, rectangular valve body sealing sleeve, the four tubular valve seals and refilled with Mercon SP fluid. Had a lot of "fun" with the connector sleeve, but got it in OK. Re-installed the Mechatronics and pan, filled the transmission while cold, started it up and ran through the gear positions as instructed, then topped up with more fluid until it ran out - temperature between 40 and 50 celsius, measured with an infrared thermometer at the bottom of the oil pan. I then took a drive down the road a bit to check it. Seemed fine, until I pulled back into my friend's driveway and did a rolling stop - bump into first is still there.

Today we're going to drain the pan to get the fluid that was in the torque converter out and refill. Is there anything we've left out? Is there a "hard reset" procedure that needs to be done? Will this sort itself out with time?

Thanks for any assistance!
Mickey

 

Transmission adaptations need to be reset with dealer software.

 

Thanks - was hoping there was something we could do without having to go to the dealer.

Will drive it a bit today before draining and filling and see what happens...

 

What you describe is infamously called "The Lurch". It has been an issue with a number of ZF 6HP26 transmissions in various automobile models for more than a decade. Some owners report successful fixes with ATF drain-and-fills and then doing the Drive Cycle Adaptations procedure. Some owners report not being able to fix it regardless of what they try. Some owners report simply learning to "drive around it". Years ago there was a website devoted exclusively to this issue. I believe it was called thelurch.com. It may still be active so you may want to check it out....

 

Thanks, Jon - will do!

And please say more about the Drive Cycle Adaptations procedure...

 

Found thelurch.com - and this:

BMW TSB - SIB240305 bulletin:

SUBJECT
Harsh 2-1 Downshift

MODEL
E60 (545i); E63/64 645(Ci/Cic) with 6HP26 up to 04/05

SITUATION
Customer may complain of the following:

An excessively harsh 2-1 downshift when decelerating to a stop, or

Transmission "bangs" into gear when accelerating from a full or a "rolling" stop
(vehicle did not come to a complete stop).

CAUSE
EGS software.

CORRECTION
On a customer complaint basis only, reprogram/recode complete vehicle using SSS
with CIP on-line update 17.01, or higher.

Important:
Transmission temperature must remain below 50 deg C and trans shifter must be
placed in P position prior to the start of CIP programming.

Looks like I'll be heading to the dealer...

 

The ZF Adaptations Drive Cycle is fully documented in Jaguar Technical Service Bulletin JTB00145 (Issue 1 was dated February 3, 2009 so Jaguar has been aware of the various ZF glitches for more than a decade now). It may very well be your next step in attempting to resolve your specific problem....

You should also seek the advice of ZF Tech Support in Chicago, phone (800) 451-2595. Ask for Steve Jaffe or Joe Laubinger. Both of them were quite helpful to me when I was attempting to resolve the intermittent rough shift issues with my wife's 2006 XK8 in 2013 and again in 2016....

 

WOW - excellent! Thanks, Jon!

 

Other things to check

• Tire pressure, especially the driver rear. The road speed comes from the ABS sensor and a tire with low pressure will not represent the true vehicle speed. This is mostly about having consistent pressure left/right rather that an exact number I suppose. Check the sticker under that arm rest for a starting point.
• Wheel bearings all around. Loose bearings give out incorrect road speed to the ABS sensors and induce bad software decisions. Double check the reluctor rings, as they occasionally come loose and give bad readings.
• Also, if you search the TSBs on jagrepair.com, there is a range of earlier XJs with problematic output flange. Apparently, there is some play with the splines and a rough transition coming to a stop. It can be tested by sitting still and going from (D)rive to (R)everse slowly back and forth a few times and testing for this lurch. It is a pretty uncommon issue, AFAIK, but it's there and worth checking.
• Transmission mount for oil contamination. Fairly cheap and easy-ish to replace. Check the rubber coupling to the driveshaft too.
• Half shafts, and grease them while you are there (seriously, grease gun and all).
• Differential either for excessive play (unlikely with such low miles)
• FWIW, some hand-held devices claim they can do the reset of these adaptations.

Best of luck, keep us posted.

 

Lots to digest - thanks!

We did the second drain and fill today. Drove it home (about 15 miles), and it was much better. It did lurch once, on an uphill stop; otherwise, it felt fine. Other stops were uneventful - no bumps into first. Shifts were very smooth (but then, they were before, as well). I'm going to drive it a bit, and then try the Adaptive Driving Cycle process and see where that lands us.

Thanks again to all for your advice!

 

Without going into all the gory details, it looks like I'm gonna need to replace the Mechatronic/valve body unit. When I took it in to the local dealer for a reflash of the software, it crashed; failed to communicate with their computer, and now I'm in safe mode. I'm assuming at this point about the only valve bodies available are rebuilt - at least any that are affordable! I've done a web search, and they are all over the map. Anyone have some good, proven resources for these?

Thanks,
Mickey

 

The gory details may help someone else with a similar ZF 6HP26 issue, so share them here when you have the time....

 

You're right of course, Jon - here goes:

In an earlier thread I sought information about changing transmission fluid due to the hard 2-1 downshift issue in my '03 XK8 - odometer reading today is ~18,500 true miles, no other transmission issues. With the help of a good friend with a lift, I drained and refilled the transmission with Mercon SP, replaced the pan/filter, the connector sleeve, the bridge seal, and the four cylindrical valve body seals. Did the proper procedure of filling, bringing it up to temperature (~40 c), and continuing to add until it started to run out of the fill hole.

After driving it a while, the issue was still there, though it did seem to be less dramatic. I disconnected the battery's negative terminal for ten or fifteen minutes while turning on the headlights. No change. So, I figured I needed to take it to the dealer to "reflash" the software. Did that last Thursday, and in the process, they said the "computer crashed", meaning the TCM didn't "talk to" their computer. (Can you tell I don't know what I'm talking about here?) Apparently, their experience has been that if the "older" (again, this is an '03 model) transmissions' electronics software hasn't been updated, there are problems with trying to do the necessary re-learning. So, the upshot is that I was told that they need to keep the car overnight with the battery disconnected, and then they are going to attempt to do the reflash. Apparently that has worked for them in the past. I was told that if all this doesn't correct the problem, then most likely the issue is a failed valve body (and TCM?), and they want over $4100 to fix it!

I will say that after my friend and I changed the fluid/filter/seals, the issue didn't seem to be as severe, and In fact, when I took a short drive with the service writer to replicate the problem, it didn't even happen. But it definitely is there, and occurred twice when I drove it to the dealership. Which got me to wondering if it was gradually getting better and would self-correct... Again, can you tell I'm in over my head??

OK, if you're still with me...!! I've restored several cars from the ground up. Mechanically, I'm somewhat proficient. But this electronic crap really irks me big time! I know in my gut that this transmission mechanically is quite fine. Remember, though the car is 19 years old, there are only 18,500 or so miles on it (documented).

So, after the car sat overnight with the battery disconnected and the cables touching each other, the dealer tech attempted to have their equipment communicate with the transmission once again. Once again, no luck. I talked to the tech (very nice, knowledgeable guy), and he shed some light for me. Apparently the valve body/Mechatronic unit has failed. Which apparently is why they couldn't get the software to communicate with each other. He also said that Jaguar is not very supportive with "older" cars' electronics (!). Looks like my choices are either replace the transmission or source another valve body and install that and go through the reflash process. I was able to drive it home Friday afternoon, though it's now stuck in third (?) gear, presumably in fail-safe mode, as trying to engage the J-gate was fruitless as well. Engine light and transmission fault message are proudly displayed on the dash...I do have contact info for ZF support (in Michigan, I think), and will be giving them a call later today to confirm all this.

Really frustrating to me, as the car has only 18,500 miles on it. (I know - I keep repeating that!) And as I said - I am quite sure there is nothing wrong mechanically with the transmission. Which leads me to try sourcing another valve body. Would be mega-cheaper than replacing the transmission, which would most likely be a rebuild and a pig-in-a-poke venture. I just have to decide now whether to swap the valve body myself and drive it back to the dealer, or have them do the whole job. Kinda leaning toward the latter, as I assume I'd at least have some sort of warranty on the work. And, of course, all this is assuming the TCM is still good..... SHEESH!

OK, with all that out of the way, and if anyone's still with me here, if you know of a good resource for a rebuilt Mechatronic/valve body, please let me know. Also, I understand the TCM is located on the passenger side of the engine bay, against the firewall. I wanted to take a look and get the ID numbers in case I need to replace that as well. So I removed the plastic cover and saw the panel held on with the four screws. Removed those, but the panel did not lift off. What am I missing?

Thanks for your patience with a greenhorn!

Mickey

 

If you cannot communicate with the TCM then something is wrong with the chip in this unit not necessarily the valve body.

 

Thanks. Just got back from the dealership, as I had to make a run into Knoxville. Had the chance to chat with the tech again, and discovered, as mentioned above, that the TCM is integral with the valve body, and not remotely mounted. His recommendation was to replace the valve body, which would include the TCM. Still trying to wade through all this and understand what my viable options are.

If the TCM can be changed apart from the valve body, that would certainly be a LOT cheaper than replacing the entire unit. But either way, it's going to require bringing it back to the dealer for the reflash - at least that's my understanding. But if changing the TCM alone does not solve the issue, then I'd have to go through yet another drain and fill, which is the last thing I want to do!

 

It is possible to re-flash the TCM with the trans empty of fluid.

I just did that.

Of course you cannot drive with an empty transmission so you have to be at whatever location you need to be to do this.

 

Thanks - understood. But in order to keep this as inexpensive as possible, I was hoping to do the swap myself, then bring it to the dealer. The alternative, of course, would be to purchase the parts and have them install and reflash.

 

Understood.

I have the software set up on a dedicated laptop so can do this myself thank goodness.

I also use Mercon SP and no longer LF6 as that cuts costs quite a bit especially if you end up doing a drain and fill a couple of times while working on faults as I have.

Anyway good luck!

 

Don't suppose you and your laptop would like to make a roadtrip to the Smokies, would you?

 

I ended up buying a low mileage transmission for my car because of valve body cost. I attempted a trans rebuild but got the same hard fault.

I believed that my TCM was fine because I could re-flash it. The unit I bought was from 2007 XKR so I had to swap that TCM for my original 2005 XJR one.

A lot of work with no lift but I took my car for a test drive today and no TCM faults.