XKR downshift jolt only 5-4?

Hi, I’m new here so hope this is the right place to post.
I just bought an XKR 4.2 S, probably should have done a more thorough test drive, but I’ve got it now, so…

When it downshifts from 5 to 4 there’s a harsh jolt from the transmission, it does this on a trailing throttle and kickdown. It doesn’t do it on any other downshift or on upshifts. It’s also less harsh, sometimes barely noticeable if I’m braking. It happens at 35-40mph.
Is it a fluid or filter problem, or more serious, and am I doing any damage driving it, everything else is fine!

Hi Graham and welcome.

Considering the age and possibly mileage of the car, the first thing would be to change the oil and filter on the gearbox. Despite Jaguar’s claims, they are not sealed for life and do suffer from age related oil.

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Thanks Jimbov8, that was what I was hoping. So, should I just try an oil change, or go for the pan/ filter change I’ve read about elsewhere? At rhe moment I’ll have to get my local garage to do it, as my garage is full if stuff, later I’ll tackle smaller jobs such as this myself.

A fluid/filter change is the first thing!!
Clear adaptations and/or reconfiguration and re-adaptation is probably in order.

MANY TSBs for the ZF6HP26 gearbox.

IDS version 118.5 or later SDD versions will have the latest software for the ‘reflash’.


Thanks for the advice, I’ll pass this info to the garage this morning. I’m not familiar with the different diagnostics/programming tools, but presumably they are universal (??) so the one they use on the other cars they service, such as my BMW will do it ?


Update: I’ve taken it to usual Garage, they’ve sent me to a local transmission specialist – they only do transmissions, on anything and everything. It’s now booked in in for a fluid and filter change and full flush next week. I forgot to ask about TSBs though, that was on my list for the garage, so I’ll nip back tomorrow.

By clear adaptations and/or reconfigure, is this the hard reset I’ve read about, remove Negative battery lead and connect to positive for 20 seconds to discharge the capacitors ?? That got me thinking that this car has maybe sat for quite a while with a completely flat battery, and only been sorted for the MOT just before I bought it, reason being is that it appears to be ‘learning’ at the moment, when I picked it up, it seemed a bit soft and lazy as though it moved into a higher gear as soon as possible., now after a hundred miles or so, it feels more like I would drive a manual.

A ‘hard-reset’ has nothing to do with ‘reconfigure’ or ‘clear adaptations’.
The TCM stores the info in a non-volatile area of the memory.
Dealer level diagnostic devices are required for these procedures.

A reconfigure must be preceded by ‘clear adaptations’. When the ZF6HP26 was introduced we had to remember to do this first but the later software does this as a matter of course.

Several older TSBs are here for you to familiarize yourself with the procedures.

S307-17 Harsh Transmission Shifts.pdf (29.6 KB)
TCM reconfigure2009.pdf (37.4 KB)
TCM reconfigure2009Trans Harsh Shifting.pdf (42.3 KB)


Thanks Bob, really useful info. I’ll talk to the transmission guys tomorrow, From what you say I guess they should know all this and may be what they recommend after oil/filter change and flush. Or do it as part of the service (???) I’m a Computer guy, so I understand what’s going on, but When it comes to cars I have spanners and half a pit! For diagnostics and stuff it has to go in somewhere where they have kit and know what they are doing. I’ll post updates here as and when…

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An update: flush, new sump and fikter all done. Transmission centre said it looked good, no signs of mechanical wear, no metal in the oil. They dont have the facilities to update the software, said i would need Jag dealer or specialist for that, but he did do a scan abd there were NO transmission error codes, just loads and loads of other old codes now cleared. Transmission seems even smoorher and quietervthan before. Still jolts 5-4 and on sekecting drive. Also threw a DSC System failure a couple of times on startup. And twice thrown ‘Restricted Performance’ after about 120 miles, with a short stop at 80 miles one time and 100 miles the other.
I have also checked battery, 12.3v then 14.4v charging. Are those figures a bit low?

12.3v is a tad low should be 12.6 - 12.8v. Give the battery a full overnight charge and see how you go.

after an overnight charge with a smart charger it was up to 12.6v, after starting, warming up and driving 20 miles or so it was at 12.8. I’ll check again later today, and do another overnight charge if its dropped.

checked again yesterday, seems to be holding at 12.6/12.7 But I’ve now hooked up a charger lead in the boot, so I can leave it on the Smart Charger whenever it’s parked and see if it ramps up. Haven’t seen the “DSC System Failure” message since the voltage went over 12.6!

All being well, that may have solved your problem.:grinning:

Still getting the failure message on startup. Then it disappears. Battery only holding around 12.6 if it’s charged constantly when not being used. Time for a new battery I think, any recommendations, Bosch Silver 100Ah for ~£130 with 6 yr guarantee looks good, but it’s lead/acid?