Its been ages since I've been forced to start a major troubleshooting/repair thread, but here I am unfortunately. There have been a few posts and threads mentioning these codes in the S-type area, but very few 'resolutions' or expert instruction that I could find. phaelax had/has the exact same symptoms with his 03 s-type R as I, but his thread was sparse, and I'm not sure he found a resolution.

Beth's history is as follows (Beth is what I named car)
- currently at 147,000 miles
- symptoms started about 140k (after a fluid change, more on that below)
- two fluid changes since I purchased her at 45,000 miles - the first by the dealer at 75k (disguised as a pan gasket leak) and the second by myself at 138k. ZF
- during the DIY change, I noticed the pan had been leaking for along time, there were signs of seepage all along one end. No noticeable problems with the transmission, however, only the occasional 'lurch' at stop signs.
- DIY change resulted in approximately 3/4 qt extra at fill time (I poured all my old fluid into the ZF bottles afterward to measure.)
- fluid level was checked again when symptoms arose, just to be sure it wasn't leaking, or the level was off. It was correct - small stream at 40deg C, never reached 50 before plug being reinstalled.

Symptoms
P0784 - 4-5 / 5-4 gear load fault (on higher loads specifically) Possible Cause: ECM Torque signal fault; transmission Mechanical failure
P0735 - incorrect gear ratio (5th gear)

Gearbox Fault lights up when I'm cruising along at highway speed, in 6th gear and an attempt to increase speed drops it into a passing gear. Dropping into 5th 'gently' is no problem, but if the TCM wants to drop to 4th, 8 times out of 10, the fault appears and won't shift to 5th. When it does function correctly (dropping down to 4th w/o a MIL), with the accelerator pedal lifted, it takes a few seconds to upshift to 5th...like its r e a l l y slow. Again, in 6th, a slight 'goosing' of the accelerator pedal often, but not always, produces a squawking sound, which I can stop by lifting again...and it almost always produces a gearbox fault MIL if it continues to downshift to 4th or 5th.

Initial 'spirited' driving from a lower gear all the way to 6th, WOT or not will rarely trigger this fault event, however, the shift from 4th to 5th is rather sloppy-slow again, yet 6th is quick and predictable.

Going up onramps in 5th or 6th gear, maintaining speed or slowly accelerating, the TCM will often downshift for me (what feels like 2 gears lower), like it is confused at a particular RPM and speed on what gear to be in.

Dealer Service Visit
I scheduled an appointment and took the technician on a short ride, where I produced the fault for him within a few miles of a 55 mhp stretch. This tech is the one that has been working on my car for the last 5 years, so I feel he's knowledgable and would take his advice if given. In the interim ride back (at a crawling pace in 4th gear), he was telling me that the TCM software update has worked well for the S-types, but he didn't see any positive results on the xk models. He could also hear my torque converter spinning....not locking up when it should. Back at the dealer, I waited for my service writer to give me the news that 'its something internal' and jaguar doesn't do repairs, only replacements - which I fully understand. There was no recommendation for a software update, nor did they even clear my adaptations, which would have been really nice, and would have eliminated any possible 'learned' behavior error as the cause.

Q. Could the previous time period, where the low fluid level create poor learned behavior over 63,000 miles of use, and now that its fluid level is correct?

Q. For those with the knowledge of the TCM software update situation (brutal mentioned it once in the s-type section, I recall), is it true that there is a risk of ECM damage with it, and do you recommend I specifically ask for said update as a course of action to avoid a rebuild?

Independent Shop Evaluation
Down the street from the dealer, there was a shop that the service guy recommended to me. He stated he did alot of their customer's work when the tranny needed some repairs. I met with the owner, and he was knowledgeable and very friendly. He had three jags in his shop, but none were the later model 6hp26 units, but he said he has worked on them quite a bit (maybe other makes - audi, bmw, etc)

His test drive resulted in the same error codes, and he too recommended a major rebuild (equivalent to a small country's gross national product ok, only $4,200)

Other References Related?
While awaiting my 2nd opinion from the indy shop, I searched the web for as many bits and pieces of information related to this tranny and those problem codes. The only 'common' potential cause was related to a single valve body solenoid (EDS 3). It is normally vented, but energized to exhaust pressure in 2nd gear and 6th gear.

Q. Could it be sticking when de-engergizing, causing the long delay and wrong pressure to enable a gear change?

The solenoid is about $110 solo, and I've been into this transmission before, i can do the labor. I've even had a valve body out of my mom's lincoln LS, so that doesn't scare me either. I'm considering pulling it, putting in a new EDS 3, and cleaning the others really well as a

Good thing is I can drive the car, and as long as I don't get aggressive in the high gears, it shifts just fine.

Below are some snippits that I found online, may or may not be valid, but it is interesting nonetheless.

Any advice, and suggestions welcome! I hope Bob (motorcarman) sees this, and recommends I come visit him and his IDS



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Before you do anything else, you may want to call ZF Tech Support in Chicago, run your issues by them, and listen to what they have to say. Last time I spoke with them (a couple of years ago), the number was (800) 660-2269....

147,000 miles is quite a load on any transmission, even one that has had multiple ATF drain-and-fills. A standard rebuild may indeed be your eventual solution. I hope that solenoid replacement will fix it for you, though....

 

I hadn't considered calling ZF directly, but it couldn't hurt I suppose. Thanks for the digits jon.

On my way home, I played around with the j-gate in Sport, and every time I manually downshifted from D(6th) to 5, or 5 to 4, I could not recreate the fault, nor the squawk either. But, just for grins, I was in 5, then goosed it, and got the noise. Further attempts resulted in it downshifting to what I think was 3rd (I was on the highway with 4k RPMs at about 55 mph) and a gearbox fault. One time in my attempts to get it to fault, it actually upshifted to 6th after the squawk...I kid you not! I could tell, because the RPMs were down in the 1500 range, and moving the j-gate to D had no affect, and I felt no gear change, but moving it back to 5 jumped the RPMs back into the low 2000s instead with the typical shift. That was strange.

It doesn't sound strictly related to that single solenoid now as once I thought, otherwise, my 5th to 3rd downshift letting the TCM make the choice, wouldn't have resulted in that MIL since the EDS3 solenoid didn't change status - remained non-energized (I did not check the fault code, however...but I may try it again tomorrow) If I can repeat it and say get a 'incorrect gear ratio' or load fault in another gear, i can eliminate EDS 3 as a potential culprit.

 

The shifting of the transmission is electronic and you have a few things to take in consideration one is the TB and the other is the transmission control module. I am having an issue with my 5 speed it was rebuilt with a control module replacement and still have the problem. I contacted ZF for technical support and they are helping. The issue is ongoing but hope to have a resolution soon. I would recommend calling them first.

I should add I have no codes.

 

Matt,
I know less than nothing about transmissions except I'm borrowing the local Carsmith's lift to do a fluid change on Monday and now I'm worrying.
Do you think it's a coincidence that the problems started so soon after the change or is it possible you did the change because the transmission was beginning to feel odd?
I'd much prefer the second explanation!

 

Steve, I was doing the fluid changes on a schedule, not a response to anything I was feeling in the transmission. If I were to do it again, I wouldn't change my preventative maintenance efforts. I think it is a unique set of circumstances that is at work here.

Please don't change your plans based on what is going on with mine.

 

This may be off the mark, but this behavior popped up on my radar awhile ago reading some tranny stuff in the diagnostics guide ( I know...get a life!). One thing that got my attention is that a leak in the intake snorkel can cause symptoms like this by fooling the tranny ECU into thinking the engine torque is wrong. I would look at the accordion folds in the snorkel before opening up the tranny.

 

thanks for thinking about me and my thread oldmots, but the snorkel is almost brand new, I replaced it recently. I've also had my air box out to get the alternator removed, and put it back together since this started acting up on me. I didnt find any signs of a major air leak. Plus, I check my fuel trims from time to time while driving, and both long term and short term bounce around 5% at all speeds.

 

I wanted to update this thread, since this particular code and transmission problem isn't seen much around here at all.

As I am accumulating the needed $4k for a tranny rebuild, I've gotten some encouragement to get the transmission adaptations cleared and reflash the TCM with the newest software. The dealer practically refused to do any reflash, and in fact told me that the system said there wasn't any updates to install for my car. They use the SDD system now, and now I know why it said that. Bob (Motorcarman) hooked up his SDD, and his wouldn't allow any reflash to occur, so he used his trusty WDS, and found my TCM software version was older than what he had available...so he proceeded to undertake this little update procedure on Friday, and I got the car back this morning from him. The car has to be totally cool to start said update/clearing, by the way.

After exiting the driveway out of his shop I thought to myself, 'oh crap, what did I just do?!?' I was babying this thing, and the transmission was shifting hard in 2-3 and 3-4, and seemed to hunt in 4-5..not to mention a really HARD slam into 2nd when I came to a stop. It was 'the lurch' on steroids... I became really worried!!!

Thinking positively, and knowing Bob didn't have the time to do a test drive, I proceeded to stay on these county roads (paved, thankfully) and put the car/tranny through the jaguar learning procedure required after a TCM reflash (I posted this somewhere else also, but can't find it again to post here) Basically, starting from rest (not in Sport mode), run the car up through the gears, being careful not to exceed 1,800 rpm on any gear change (keeping it as low as possible yet gaining speed to initiate a gear change is the key), all the way up to 6th (about 55 mph) and then release the accelerator, allowing the car to naturally decelerate and downshift on its own...it takes awhile to slow to reach all the shift points, but its important not to brake for the car until it downshifts into 2nd. The first few times I tried this, it wasn't slow enough, and I got a 2-3 gearbox fault every time. All hope was fading...

The process needs to be repeated for at least 5 cycles, but for good measure, I ran my car through it 10 times, and as the next cycles came and went, the shifts became more smooth, and at the end of it all, not only were the upshifts perfectly transitioned all the way up, but there wasn't even the slightest hint of 'the lurch'. No more gearbox faults at these light shifts either. To be honest, my car has lurched from day one of my ownership, I thought it was inherent, and I would be forced to live with it. It seems a clearing of the adaptations, with new software (I'll try to get the TCM software version next time I get inside the brain with WDS/IDS) and properly training the transmission can cure this annoyance.

Now, as for if this procedure has corrected the noise and 4-5/5-4 gear load fault and 5th gear incorrect ratio, only time will tell. Bob recommended several hundred miles of cautious driving before testing the higher load shifts. Keep your fingers crossed for me! $4k in savings would be a beautiful thing...though I am not counting those benjamins just yet.

 

Now you know that Bob wouldn't steer you wrong.

You members who are close enough to drive over to Motorcarman and Brutal are the envy of everyone else on JF.

 

FYI

After much discussion between the trans shop and ZF it was suggested that my problem could be an electrical command issue so I put the car on the lift and began to check connectors and connections. What I found was that the bayonet connector was not closed all the way on the transmission. Shame on you Trans Shop! So my action was to clean the connectors at the transmission and at the transmission control module. So far the transmission has been shifting smoothly and properly. Only time will tell if I found and fixed the real problem. Reflashing the control module was a thought but will see what takes place.

Matt I hope your fix works for you.

 

That is indeed great news. I also hope that your ZF problem is resolved and that you can keep your four grand in your pocket. Let us know how your ZF behaves as you rack up more miles after the software reflash....

And I concur that those of you close enough to Motorcarman and Brutal are very fortunate owners with a distinct advantage over the rest of us....

 

Hi,

I'm not as lucky as H20boy...since I have my XKR MY2003 I had very scarcely a « gear fault » message with DTC P0784 and P0735.
In december I found a way to reproduce the problem. I have to drive on motorway around 130 km/h then "pedal to metal...". Sometime, I have harsh downshift from 6 to 4th (I think) and in this case I get the message gearbox fault (gearbox stays in 4th).

The car is a XKR2003

What I have done :
- The gearbox oil has been changed 2000 miles ago without improvement.
- The gearbox has been flashed and cleared (the local dealer was not very happy to do this job...the first trial has been a fiasco but succes comes at the second visit to dealer).
- After that, I have done the adaptaion cycle at least 10 times
- I have checked air leaks but nothing found.

What I am now prepared to do:
open the pan in order to check electrical connexions.
order a solenoïd kit but where in Europe ?? it seem's easier to find them in USA !
Buying a used gearbox (Jaguar spares days are not so far now)
One other idea is to use the ZF additive to cure the known Sqwak issue on ZF 6HP26 (mine is in the range affected).

Welcome to your opinion!!!

Regards,

Daniel

 

It has been awhile since I posted on the fate of my transmission, I wanted to conclude this saga with news of ultimate success. The fix, however, was not only limited to the efforts of Bob and a simple adaptation clearing and a TCM software update. My problems were more internally related and mechanical in nature, and finally led me to the only option remaining (and most costly one as well) to rebuild the ZF 6hp26, and address another unforseen, yet an ultimately critical component responsible for my 5th gear nightmare. Total cost - $4600

The rebuild went great, my selected shop was down the street from the jag dealer, and recommended for this type of work. Original ZF parts kits were used for the rebuild, and the torque converter replaced with a rebuilt ZF unit also. I cringed when I found out he didn't use the Lifeguard 6 fluid (i think it was Mobil 1, but I don't have my receipt here with me at work to double check) but he assured me he uses this all the time in the ZFs, and it is compatible. After driving it for 1000 miles or so, I no longer worry about that being an issue. The owner of the shop also is warrantying this for 3 years...even told me he would stand behind it as long as I own the car and he's alive -he's that confident in his man's work.

Getting back to the transmission now. In addition to the normal clutch parts and seals, he disassembled and cleaned my valve body, and put in Sonnax upgrade parts, specifically - the ZF6 Zip kit, which has all the o-rings, new A clutch control boost valve and sleeve, oversized pressure regulator sleeve, springs and end plugs...pretty comprehensive kit, and at only $125, its worth adding with the rest of the hard part replacements in the transmission.

Unfortunately, the rebuild items alone didn't fix my sqwaking sound OR my fault. His test drives following the rebuild turned up the exact same noise, and corresponding transmission trouble codes. He and his long-time transmission builder took the entire thing apart again, and together measured everything, double checked each part, put it back together and into my car, and it happened again. We met for drinks and a burger, tossed around some theories, and the next week, he had discovered the reason...well, at least narrowed it down, to the valve body casting itself. Having a core transmission from an s-type, he pulled its valve body, put my TCM into it, and tested the car with this donor part. No more sqwak or fault. I was elated to hear he found the cause, but he told me that when he pulled it back out to do all of the Sonnax upgrades to it, he inspected and measured the bores, compared them side by side, and couldn't actually find what the exact issue with my valve body contributed to that fault. Without going into forensic examiner mode, he proceeded to 'refurb' the s-type valve body with all the same goodies, and that is now transplanted into my xk8.

A long, frustrating diagnostic path leading here has finally ended. I was really worried that I would have to buy a salvage transmission with unknown origins or longevity. I now can enjoy the car for many more years and hopefully pass it down to someone else with full confidence in the repairs made to it. Its over 150,000 miles, and I fully expect to take me over 200,000 before I even consider selling it or giving it to one of my three nieces. (currently ages 17 down to 12)

Daniel, your symptoms sound VERY similar to what I experieenced. i shudder to think about those downshifts and upshifts... and how much anxiety I had over whether it would throw a fault or not. Pulling over to the side of the highway to shut the car off and start it again irked me to no end...allowing passing motorists the opportunity to smirk, vocalize to themselves or their passengers, the jaguar reputation of old... that "all jaguars are unreliable and the always break down." You may have to go down a similar path as me if your fluid change doesn't work and the issue gets progressively worse, more frequent, and to the point where you can't even avoid a fault when accelerating in those higher gears. Before a transmission rebuild, however, or even a used gearbox risk, I'd pull your valve body out of the transmission, take out your TCM, and put a refurbished valve body (only $850) with your TCM placed back into it.

 

Glad to learn that you believe you finally have your XK8's ZF fixed, and I think you'll be just fine with the Mobil ATF in it. I'll keep my fingers crossed for you. Keep us posted as you put on more miles....

 

Thanks alot for your reply!

but not good news for me...

I will give a feed back as soon as I will decide the best way for my gearbox.

Regards,
Daniel

 

sort of good ending. but the first step from zf/jaguar has been to reflash which now automatically clears adaptations and driving to relearn. doesnt meen its works in all cases, but its better than cutting off the leg first for an ingrown nail. (and much cheaper)

 

I'm currently dealing with the P0735 code on my 05 S-type, the fluid and filter was changed about 5k miles ago. I just drained the fluid again and it still has a black tint. I'm hoping the new fluid makes a difference but after reading the solution to your problem I don't have my hopes to high.

 

As far as I know 03xtype, I'm the only one to take it as far as the rebuild to find a solution. Again, as mentioned before, a valve body swap w/ your TCM is alot quicker and would be definitively cheaper along your diagnosis path. A full rebuild would be the last possible option.

 

do you know if the dealer has updated the valve body over the years or is it the same design?