Hey, I recently started having problems with my 2003 STR. The car has about 125k on it and it has been very reliable up until now. When I put in in drive or reverse, it drops out of gear after a few seconds. It does the same thing when I stop at a light. It feels as though it doesn't have enough fluid (It does, checked this morning). After I get it going it shifts and drives great. Any thoughts? I have checked fluid, it was clean and smelled good. I though maybe a pressure regulating solenoid (wouldn't this affect all shifting?), a clogged filter, or some sort of electrical gremlin.

 

There is quite a wealth of information on this forum regarding the ZF 6HP26 gearbox and the faults that can be experienced. Perform a search using your symptoms and you may find several relevant threads.

 

Have you tightened the two 8mm bolts underneath the car that attach the shift cable to the side of the ZF unit? If not, do so and see if that cures your problem....

 

Thanks Jon89, shift cable is a fantastic idea I will have to check that out tomorrow. I have tried googling everything and have come up with nothing so far.

 

How did you check the fluid level?

 

First I spent 2 hours trying to make an allen key fit between the transmission tunnel and the fill plug, then I pulled the plug while it was running. It had a little dribble out the hole but I am not exactly certain how hot it was.

 

You should have a steady drip between 30-50 Celsius.


I agree with Jon, those 2 bolts have been known to come out, then the car wont know what gear its in. If they are loose, pull them out, put some Loctite on, preferably the blue, and reinstall.


Do you get any warnings on the dash? Or when selecting gears, the J-Gate doesn't always light up, or the wrong gear is lit up compared to what gear the car actually is in?

 

No lights or warnings of any kind. The lights on the shift gate have been working as far as I have noticed. I only have trouble when I first put it into gear or stop. If it is moving, it drives smoothly like it always has. And when it is warm, it tends to have fewer problems. Im just completely stuck as to what it could be at this point and the local Jag place is unavailable until Tuesday.

 

Original fluid? I'd start with a fluid change following tightening the shifter linkage.

 

O yes, nothing but 45$ a quart at the dealership for my STR.

 

Have a look at this vendor:

6 Speed oil change kit Jaguar

 

Still looking forward to your intro in the new members section.

 

So I dropped the valve body this weekend and disassembled for inspection. Nothing appeared worn. All of my solenoid tested at the correct resistances. I put a few new quarts of fluid in it on reassembly along with new "bridge" and "connector" seals. It drove great for 2 days without a hint of a problem, but when I started it up this morning the shifting issue was immediately back. Does anyone have any logical reasoning as to what would cause an inconsistent such that it will sometimes drop a gear and other times drive nicely? Possibly a computer problem? What exactly controls clutch pressure (which solenoid(s))? The information and misinformation about this transmission is extremely confusing.

 

These ZF 6HP26 transmissions supposedly adapt to the driving style of the owner over time. They have been known to "drift" after a few years and begin acting up (meaning poor shift quality, especially in the lower gears). Jaguar realized this around 2009 or so and came up with a process to "reset" the ZF back to square one and allow it to re-learn the owner's driving style again. They call it the ZF 6HP26 Transmission Adaptation IDS Procedure (JTB00145)....

My wife complained about poor shift quality in her 2006 XK8 at about 67,000 miles back in the summer of 2013. Rick (joycesjag) and I did a ZF pan/filter, sleeve, and ATF refresh (using Lifeguard 6) in mid-July 2013, followed by the ZF adaptation procedure at a Jaguar dealership in Greensboro, NC that I really trust. Those two actions absolutely fixed her poor shift quality, restoring the car to smooth-as-butter shifts throughout the range once again....

It stayed that way until a few weeks ago when she began complaining about the exact same poor shift quality once again (the car is now at 100,500 miles). My scanner showed a P0782 code which means a 2/3 and 3/2 gear load fault resulting from an incorrect calculation during gear shifts. I cleared the code, it has not returned, but the poor shift quality is still intermittently present. So Rick and I are planning another ATF drain-and-fill, this time using Mercon SP. If that doesn't fix it, then I'm taking the car back to the Greensboro Jaguar dealership for another ZF adaptation procedure. I called them last week, told them of my plan, they checked and did not have the software anymore because no one but me has ever asked for it, so they downloaded it from Jaguar Corporate and called me back to say they are ready whenever I am. They will charge me $150 for the procedure, well worth it if it gets my wife happy with her car again for a few more years....

You may want to check out the ZF adaptation procedure at your local Jaguar dealership. If they say they no longer have it, they can download it for free from Jaguar Corporate. It takes about two hours to download, so make sure they know this....

Good luck and keep us posted....

 

Just for anyone reading this thread in the future:
I have recently swapped out my solenoids with a used set that was known to be functioning when removed. The exact same problem reappeared after a few hours of driving. I have since decided it is in fact a computer issue as Jon89 suggested. When I am aggresive when shifting into drive or reverse, the gear-dropping issue disappears for a little while. I also did the "shift relearn" procedure of coasting to a stop from 55 mph (repeated 6 times). This also seems to cure the issue for a little while. Although every transmission shop, including the local Jag specialist, insists I have a failing transmission (no one can explain how it is failing, just that they need to perform a cash-ectomy), I am conviced it is a TCM issue. I am taking it to the nearest dealer on Thursday for a software reflash and possibly and adaptive relearn (JTB00145). Moral of the story, putting in a new transmission to fix an obvious electrical problem is like buying a new house because your toaster isn't working.

 

Don't beat yourself up, though. The - detailed - inner workings are rather a puzzle so thanks for providing a bit more insight.

We know more than one version of the software inside the TCM has been released (several, I suspect) and that the current version can be read out (I read mine using an elm327 but IDS/SDD can do it I expect). IDS will always be wanting to put in the latest for the car (based on VIN).

Overall, the TCM & PCM co-operate e.g. during gear changes but also to avoid them (such as during hard cornering). Engine issues have been seen to upset the gearbox for physical/electronic reasons (misfires are an example) so we know that a properly working engine is needed.

Coast downs are used by the PCM as part of its (re)learn. I don't know what if anything the TCM uses them for.

All great when working but can make you long for a simpler era.

 

For anyone searching for this thread:
Problem was solved today for 40$. In the last few days, I had a misfire develop which turned out to be a coil failure. After changing the faulty part, my transmission issues dissapeared. The failing coil started causing transmission issues a month before I saw any problems with the engine misfiring. After lots of troubleshooting and tearing apart a valve body... the problem was in the engine. Its amazing how sensitive the electronics are in these cars.

 

Don't beat yourself up too badly. There are at least two former members of this forum who had their transmissions completely overhauled (costing thousands of dollars) when their actual problem turned out to be a failing battery....

 

Apparently the tiny (physical) engine jerks can upset the trans - not that the trans posts any codes to say so - and you've suffered. Well done finally fixing it!