Hello guys.
I am pretty new with the cars at all.
And it happened that way that now i have a Jaguar XJ8 2004 with 82k miles on it. I bought it for 5600$ and it was inspected by mechanic in california and he said its beautiful car in perfect condition for its year.

So i bought it. I made 5000 miles on it in 2 moths without any problems and was VERY happy with that car. It is so nice to ride it - always a pleasure.

But **** happens. Few weeks ago, i was driving on highway around 95mph, and then gear shifted down, and "transmission fault" appears on the screen.
I parked. Wait few minutes - and continued driving without any problems or messages. But i wasnt so fast after that. I made around 500 miles after it - without any problems! And then - in a traffic jam - i recived that message again! On a pretty low speed. After paring and turn ignition off - error disappeared.

After that i made at least more 200 miles on it without any problems or errors.

So for now car driving very good and smooth. Only thing i can mention - it runs engine on higher RPMS (becasue its louder) - when in the first day drive with cold engine i am on 2 speed and i am not pressing gas. If i would apply brakes slightly - engine becomes calmer and quieter. And it happens only in the mornings when car is cold. But thats all. I can drive on highways till 90mph or stay in traffic jams - there is no problems at all. Tranny works smooth!

But i know that repairs of jag could be crazy expensive. So i decidet to show it to mechanic. I know that there is a lot of reasons for that message except tranny mechanical issues.

I showed car to mechanic in Los Angeles. His conclusion -
- P0730 (incorrect gear ratio)
- P0735 (gear 5 incorrect ratio)
- P0736 (reverse incorrect ratio)

He inspected fluid in tranny and showed it to me - its pretty dark (burned he said) and there is shiny tiny spangles in it. Like super small metal pieces. But not a lot of it. I can even say they are almos unnoticable.

He said fluid level is ok, there is no battery problems, no leaks on the connectors and cords and sleeves. Engine is in very good condition. Air suspension too. He didnt say anything about plugs and coils, but he seems professional enough not to miss it.

So he think it might be mechanical problem in the gearbox.

And then he said - we can change fluid in it. And it might help. But becasue fluid is dark, and have some metal in it - condition of rubber parts and gaskets in tranny can be poor, and they might be destroyed by procedure of changing fluid. And it will kill it in a moment.

So he said i can still drive my car - and it might take even few years for tranny to turn completely dead, and then i can replace it (5000$ or more! Price of a that car!)

or i can try to replace fluid - and it might solve the problem at all. Or kill my tranny immidiately.

Any ideas what should i do? Is it really so risky to change that fluid? I dont know should i be so cautious and alert - becasue car showed me errors only two times in last 700 miles and i am not shure my tranny so ****ed up by now?

Thank you!

 

PS

Just saw on forum: "Definitely change it, but just drain it, do not have it flushed. "

May there is something my mechanic doesnt tell me? You can change fluids few different ways? With flush (which my kill rubber) and without?

 

Transmission Flush, When and when not to flush transmission | MDH MOTORS

read the bottom. i wouldnt worry about the dark fluid condition since thats just what happens with age.

i would worry about the metal specks. another way to determine how the transmission is doing is getting the oil analyzed by someone like blackstone (google them, ive also used them before). another thing you can do is pull the pan/filter off and check the magnets to see how much metal is stuck. this might be a better barometer ... but the problem is that you have to drain the fluid! maybe you can just refill with old fluid thats been run through a fine filter to get rid of large particles.

also maybe a second opinion could help

 

My experience from ZF tranny expert is without removing the pan and inspecting the transmission. You are just speculating.

Take the car to ZF transmission shop (BMW, Audi use exact transmission). I would remove the pan and replace it with fresh filter and do simple inspection. It may be an inexpensive fix (like a selinoid or sensor). If the visual inspection is inconclusive; then I would refill the fluid and drive it.

https://en.wikipedia.org/wiki/ZF_6HP_transmission

ZF 6HP26 is considered a very reliable unit and even 100K is nothing on them. They normally last to 250k+ range. They only flaw is that the fluid isn't sealed for life. It should be replaced every 60-100k miles. It is also very under stressed in 4.2 Jag V8. They designed it to handle way more power.

In summary, get a second opinion from a ZF transmission expert.

 

Read, watch the videos, take your time, ask questions, when your not sure; Mercon SP, (have eight quarts) steel pan, heavy gasket from Ford, with filter, (think its from the Cobra) for the conversion, and fluid change. Saves you a lot of cash and not all that hard a job. A laser temperature gauge come in handy, Harbor Freight sells them cheap, mine worked out well. Good Luck

 

Hi Alexey,

The fact that your mechanic checked for oil leaks in the electrical connector sleeve makes it sound like he knows something about these transmissions.

Regarding the three diagnostic trouble codes (DTCs) P0730, P0735 and P0736, Jaguar lists the same two possible causes: ECM torque signal fault, or Transmission mechanical failure.

If I'm not mistaken, there are multiple ECM torque signals, all communicated with other modules over the CAN bus. The ECM and TCM work together to manage torque for smooth gear shifts. A fault in one of the ECM torque signals might trigger one or more network DTCs, which have a U-prefix (for Undefined). If your mechanic has a system capable of reading the proprietary Jaguar U- codes, he may find one or more of them have been triggered, which may help you determine if your problem is electrical or mechanical (look for U- codes related to the TCM, Adaptive Cruise, or Dynamic Stability Control).

Regarding the transmission fluid, I definitely think it's worth doing at least a drain & fill, and as long as you use Motorcraft Mercon SP or ZF Lifeguard 6, you should have no problems flushing and replacing all of the old fluid. This alone may improve the performance of the gearbox, but you may also need to have the old Mechatronic adaptations cleared and the firmware updated to the latest version available. This process cured harsh shifting on a friend's '05 XJ8L.

Cheers,

Don

 

Thank you all for your advices.
I really really appreciate it. I have learned a lot of new things!

I am considering to look for tranny mechanic who knows ZF here, in LA and show car to him.

Thank you again, guys!!!

 

UPDATE!!!

I called previous owner - and he told me he CHANGED FLUID and pan on 70000 miles!

Woah. I didnt expected this. Any thoughts then? I am understand right that its not making sense to change fluid again after 12000 more miles?

 

Hi Alexey,

Can the previous owner tell you exactly what type of transmission fluid was used when it was changed? If it was anything other than ZF Lifeguard 6 or Motorcraft Mercon SP, the fluid may have caused internal damage in the transmission.

Don

 

He told me it was right one ZF fluid. Also i found checks for changing all spark plugs, replaced mass air flow sensor, both O2 sensors, fuel filter.

And i found one strange note in a check just before car was sold to me:




what does it mean?

 

There are at least two issues involved here:

First, on the ZF 6HP26, the transmission control module is built into the valve body, and ZF calls the combined TCM/valve body the Mechatronic or Mechatronik. It's programming is designed to adapt to your driving style (smooth and slow, fast and aggressive, etc.). It is also designed to adapt to wear of transmission internal parts as well as changes in the fluid slippage characteristics over time. When the fluid is changed, these stored adaptations may no longer be optimal for the slippage of the new fluid. Given time, the transmission control module should adapt to the new fluid, but the process may be jump-started by clearing the old adaptations.

The second issue is that ZF periodically releases improved and refined firmware programs for its electronically-controlled transmissions, providing revised shift maps, more effective adaptation capabilities, etc. Clearing the old adaptations and updating the firmware in your transmission may help reduce or eliminate harsh shifting.

Updating the firmware requires the correct Jaguar dealer-level equipment and the correct program files.

Cheers,

Don

 

Thank you so much again for all the answers, folks!
I started that thread with 82k miles, having some tranny errors with check engine light. After I created that thread in a week I cracked my transmission plastic cover by a huge rock, so I got it replaced together with fluid. And you know - it helped! For the next 20.000 miles I got no transmisson errors, and no check engine light except bad oxygen sensor.

But now. at 103.000 miles in last two weeks I got message "Transmission Fault" three times, but no Check Engine light. And when it happens it feels like car is not coming higher than 3rd or 4th speed. If I stop the car and switch off the engine - error gets away, and transmission works flawless for next couple of days. It feels like it happens when I am not gentle with my gas pedal, trying to speed up quickly for example. And it never happens if I am driving careful.

So can I do anything good for my car now? Should I replace tranny fluid again? Now I am at 103k miles, and it was replaced at 82k and probably at 70k too by previous owner.

Or should I just drive it till tranny will finally die? To be honest I dont have money to rebuild it

 

I would check fluid level first

 

Hi Alexey,

I'm happy that we're finally hearing back from you, but sorry that it's due to a new malfunction. Probably the easiest next step would be to have the vehicle scanned by a system capable of reading the proprietary Jaguar diagnostic trouble codes (DTCs), which may tell you why the engine control module and transmission control module are triggering Limp Home Mode and/or Restricted Performance, which locks the transmission in one gear (usually 3rd or 5th) to help you "limp home." Plenty of issues can cause LHM or RP that are not internal to the transmission, so knowing what DTCs are stored will help narrow down your diagnosis.

Please post all codes here exactly as they appear and we'll try to help. The codes begin with a letter (P, B, C or U) followed by 4 or more numerals. Be sure to write all of them down, even ones you don't think could be relevant. For example, a problem with a wheel speed sensor or the mass air flow sensor can cause transmission malfunctions.

Cheers,

Don

 

My '98 XJ8 had broken a timing chain when I bought it ($800). Had 252k on odo. I bought the tools and did the engine, but once running I took to a reputable shop for the tranny oil. Since it's a sealed unit the shop used a cleaner in the old oil, then changed with another can of cleaner. They then flushed everything out and installed new fluid. It was a bit costly ($650), but these transactions aren't easy or inexpensive to work on! I'm now confident this oil will last as long as I own the car.