I'm keeping my fingers crossed hoping the fix is permanent. Good news. Maybe the DSC sensed some slippage and interfered with the uprev. I'm just guessing. You must be happy to have it fixed.

 

DGL, that does sound like a plausible explanation. It's weird, the drivetrain just seems much more direct, especially when letting off the throttle.

 

Like everything good in my life, there is a catch to this. I now have a check engine light on. Car is still driving great, but I will scan the code tonight.

 

Well, 20 days later, I experienced the lazy downshift problem this morning. However, if it only happens once a month I'll be happy. Seems like a lot of you guys have the same issue, but very infrequently.

 

I drove a lot of miles this weekend in the XKR--probably about 100 or more. The paddle shift issue kept popping up after extensive use.

I seemed to be able to control when I could cause the glitch to occur. It seems to happen most frequently when you are going up a grade with moderate throttle. Then if you hit the downshift paddle, I think the TCM must get confused with how much throttle blip is need to revmatch, since you already have your foot on the gas pedal. Then after that, all of the downshifts are lazy and don't occur correctly until a restart.

Of course it's still possible, even likely, that this is a battery-related electrical gremlin. I look forward to the day when I can have the car plugged in to a power receptacle but right now that is not possible. Until then, I will probably buy another AGM battery to replace this one. I hear there are much cheaper options than when I went through this last time.

I am starting to become indifferent to this car. I understand it has special needs (a battery charger life line) but getting a fun performance car with an automatic transmission was already a huge stretch for me. Having this particular gremlin is sort of killing the magic for me...

 

Have you changed out your battery yet?
Since you can't plug the battery tender in where you park, can you use a solar panel charger? If there is "some natural light" it will help or use it when parked outdoors..say at work???
Sorry to hear of all these problems. Very frustrating.
I don't use a battery tender by the way, but lock the doors every time I get out....Been two years so far and only drive it 2-3 times a month. I am keeping an eye out for any glitches tho!

 

I changed out my battery about a year ago, which seemed to solve the problems, but those problems came back just a couple months later.

I am using a solar charger, but I am parked in covered parking (with some natural light). Unfortunately, I don't think the solar charger does anything because the opening to my parking space is facing north, which gets very little light.

I wonder if this issue is limited to 4.2 XK models. I have never heard anyone with a 5.0 have these problems. Is it a good excuse to upgrade?

 

I had this issue for the first time today since I got my '08 XKR last summer. I also noticed, when in D and not using the paddles, that the gearbox seemed to struggle to make up it's mind what gear to use. I got home, checked for fault codes, cleared them and stopped and started the engine.

Seems fine now... For now...

Fault codes were "U0402:
Type Network - Network Data - ISO/SAE Controlled Description Invalid Data Received From TCM


and
U0405 - Generic Type Network - Network Data - ISO/SAE Controlled Description Invalid Data Received From Cruise Control Module

 

8bit, this is very helpful--most of us with this issue just chalk it up to an older/weak battery, but haven't actually digged deeper to see what was causing the problem! What sort of scanner did you use? This doesn't sound like the typical OBDII codes--or at least not one I've heard of!

 

Battery doesn't seem entirely unlikely, that's the first time I've known this car do this and it's been fine since it did it yesterday. I used an Android app called Torque Pro using an OBD to Bluetooth adaptor. Looking at the workshop manual it seems there are several different versions of each of those codes; the "official" Jaguar ones have two further digits at the end which give some more specific information. I guess I'll have to get some sort of Jag-specific code scanner to find out for sure.

Have you had your transmission serviced since you first noticed this?

 

I think the transmission is working fine, I think it's to do with the engines brain.

IMO update the engine and transmission module to the latest firmware. That would be a good place to start.

 

The gearbox is different - the 4.2 has the ZF 6HP26, the 5.0 has the 6HP28, which is significantly better. It changes faster, locks up the torque converter in every gear where possible, and can skip up to 4 gears when changing up or down.

 

Wow, I can't believe I didn't realize the 5.0 XKs had a different transmission!

 

Yeah, they didn't really make a song & dance about it when the 5.0 came out - too busy singing the praises of the new donk. But it's a significant contributor to the increased performance. It figures out what gear you need to be in within 100ms of you changing your inputs (e.g. stomping on the loud pedal) and completes the change within 200ms.

 

How can I tell if the current firmware is out of date? Jaguar TOPiX says there are no outstanding recalls for my car and the dealer claims they check it at service time...

 

The TCM software and/or maps might be up-to-date, but they might have been corrupted. Re-flashing the TCM could cure the problem, or it may have no effect. Worth a try, though, if it's really bugging you.

Also, what's your mileage, 8bit? Could it be time for a transmission oil change?

 

I had my TCM reflashed and the lazy downshift issue eventually came back.

 

Mine's done about 77k miles. I called the dealer I bought the car from recently, they checked the service history it had with them and they had no record of the transmission fluid being changed. It's on my to-do list but I thought I'd read somewhere that the 6HP26, when showing this symptom, might need the mechatronic solenoid valves changed as well. They're accessible once the transmission pan is off, by removing the mechatronic block.

Thanks to moar's very useful video I'm happy to change the tranny fluid myself, if I can get the solenoids then I think I can do that too, but I guess reflashing the latest TCM software is a dealer job? I guess I'm slightly wary of doing that (and presumably paying a tidy sum for it) given that amacdonal86 found the issue came back...

 

8bit, I have heard the same thing.

The TCM reflash is about a 1 hour job ($130 or so), so you won't be out a whole lot of dough if it doesn't work. It's not reprogramming the TCM, just clearing the adaptations. I think reprogramming the TCM is significantly more time consuming.

 

Well if it is just clearing the adaptions then I guess disconnecting the battery for an hour or two should do the same job. Which (and I'm making a bit of an assumption here) would possibly point back to battery issues causing the corruption in the first place...