I know there are several possible quirks with the 6HP26, but have not found anything about my symptom. Here it is:

At highway speeds, say 70 MPH, when I get off the throttle completely there is sometimes a sort of "lurch". It seems from the RPMs that this is not an upshift or downshift, so I'm thinking it's the torque converter unlocking or locking abruptly (it would want to unlock in this situation, right?).

When this first appeared, I thought it might be battery-related. The old one had marginal rest voltage, so I replaced it and thought the symptom was then gone. Either I did not test fully or, if it was gone for a time, it is back.

Anyone familiar with this? Is there anything I can do in the way of a drive cycle that might effect this behavior?

(My understanding is that the transmission's learned adaptations would not be cleared by the standard "hard reset" procedure, true?)


TIA.

 

https://www.jaguarforums.com/forum/s...-theory-24552/

 

Thanks, Paul

Seems the 6HP26 can be a troublesome box. I need to do more testing to be sure of my facts, but seems in my particular case it's not an actual shift taking place ... more like something the torque converter is doing.

Any suggestions on how best to proceed will be much appreciated. When the symptom is present it will drive you crazy: As we often have to do in highway driving ... apply a little throttle, coast, a little throttle, coast. This becomes throttle, coast, lurch, throttle, coast, lurch. Ugh!

Editorial comment: The "old technology" 5HP box in my '01 XK8 was untouched and pretty much flawless through 95k miles. I'm just saying ...

 

Dennis,

In the early summer of 2013 my wife began complaining of sporadic upshifting issues on her 2006 XK8. They were intermittent and a bit unpredictable. No messages on the dash or codes for a code reader. After a month or so of her kvetching, and with the car at about 67,000 miles, I decided to order the pan/filter/sleeve/fluid kit from Klaus in California and do the ZF service. Afterwards, she was happy for about 500 miles and then began reporting the same issues. So I did some more research and decided to try the Adaptive Drive Cycle procedure at the Jaguar dealership in Greensboro (80 miles away) that I trust. They told me that for situations like my wife described, this has succeeded about 85% of the time with the 6HP26 box. They charged about $100 less for this service than our local Jaguar dealership quoted me (and they have two master techs with more than 25 years of Jaguar experience each) so it was well worth the trip....

I scheduled it, drove the car there on the appointed morning in late July 2013, they performed the procedure, and the ZF has behaved normally ever since. The car is now approaching 81,000 miles....

Do some research on this Adaptive Drive Cycle procedure. It may solve your issue. But before you schedule it, get underneath the car and look for ATF leaks. You could just be low on fluid....

 

Thanks, Jon

Everything looks dry underneath. About 44k miles, BTW.

Is the procedure you're describing the one where they reflash the TCM and then take it through a precise drive cycle while monitoring certain stuff via a connected PC?

A few hundred $$ total, correct? I've seen posts saying this is not a job for an Indie.

 

Correct. Do NOT go to an indie for this. Most indies have never done it. Call around to your area dealerships. Prices vary. So does their techs' experience level. If they do not sound knowledgeable about the procedure over the phone, keep looking until you find a dealership that is credible, even if you have to drive some miles to get there and back....

The Jaguar TSB is JTB00145, "ZF Transmission Adaptations Drive Cycle - IDS Procedure". To do it correctly requires at least 90 minutes. Anyone who says they can do this in 30 or 45 minutes is blowing smoke....

Good luck, and if you decide to pull the trigger on this, keep us posted of your results....

 

Shouldn't this car have a 5HP24?

 

Just wanted to report the outcome of my issue ... at least for now.

From experiments ... The "lurch" behavior I described above seems to occur when my car's 6HP26 is right on the cusp of downshifting from 6th to 5th. Often no downshift actually occurs, but the box seems to be hunting. (No other shifting problems have shown up so far.)

This is a "highway speed" issue. When road speed is hovering near the "lurch" point, things can get pretty annoying ... lots of lurches in traffic at highway speeds where lots of throttle changes are needed.

The speed where this occurs can be changed in a repeatable way by changing from Sport to Cruise mode or vice versa. (it's something close to 70 MPH in Sport, somewhere in the 50s in Cruise.)


Two things that have helped:

1) By selecting either Sport or Cruise mode as appropriate for current road speed, the annoyance factor drops a great deal ... to hardly noticeable.

2) I did a hard reset (from what I've read this probably didn't matter) and undertook a 100+ mile drive-cycle trying to encourage moderate-torque shifts through all gears. It seems as though this has improved things, but I can't rule out a placebo effect on this one.


Anyway, unless something goes south from here, I've got an acceptable solution.

 

Hope it works for you. Keep the Adaptive Drive Cycle procedure in the back of your mind in case your situation worsens again....