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Hi everyone. I know this sort of thing has been discussed before, so I hope you will forgive me for the post. My 2004 XJ8, bought last December, has ca. 62000 miles on it, and on Sunday an amber light displayed with the "Transmission fault" message on the dashboard. I was driving on an Interstate at the time, nothing stressful for the car, and continued on to an exit that would take me to my local Jag dealer, where I dropped it off with a note. I had to stop at an intersection once I left the highway, and the car went into limp mode, i.e. wouldn't shift out of a very low gear.
The dealer called me yesterday (Tuesday) and said they got code P0829 - and that the transmission was finished. They said they could install a new one or rebuild mine for somewhere between six and eight thousand dollars. That is not something I can afford, and I then considered simply having it towed to my place and using it as an elegant setting for tea parties.
But that evening, the mechanic at the Jag dealer called back to say that they had found a used transmission out of state that they could install for a grand total of $4500, with a one-year warranty. That was encouraging, and I was happy that they were trying to come up with an alternative. I then dropped by a local indy shop that has done some work on my car (I have split work between them and the Jag dealer over the past few months), and they said that based on the code and what the dealer told me, they could rebuild my transmission for roughly $3500 with a one-year warranty (and for an extra $150 they would make it three years).
So, my question: any concerns regarding a rebuild rather than a used transmission? The $3500 sounds much more doable, but of course I'd want to be confident that I don't lose something with a rebuild. (The indy shop is Becker's in Naperville, IL.)
Another mechanic, who lives 2200 miles away (a friend of a friend) was very skeptical that I actually need a transmission, but I hadn't yet given him the error code.
Oh, and the transmission fluid had only a thousand miles on it or so (that was what Becker's had done in April, plus a new transmission fluid gasket). I don't abuse my Jag, although I do enjoy driving it fast (100 mph) on the expressway every now and then.
Back in early 2014 my Jag's transmission started slipping gears during brisk highway acceleration from on-ramps. Would go into limp mode and display a gearbox error. I found that turning off the engine would reset the error and the car would drive normally in city stop and go traffic, but once brisk acceleration was attempted - gear slippage and limp mode would ensue. The Jag dealer kept it for a day testing it and said a factory remanufactured transmission was the way to go for about 8 grand. I declined and asked my local indy to keep an eye out for a used transmission. One came available - a Jag was written off locally by an insurance company after having been in a major crash, but the transmission seemed undamaged. The indy said I could buy the used unit for US$1,600, and they would install it for US$800 additional. The used unit had 50k on it. I agreed to this. It has been well over a year since then and I have had no problems with the used unit. It had no warranty being a salvage part taken off a wreck, but that was 15k ago so I have been happy with it and it has performed without fault since it was installed. Granted buying a used part carries risk, but sometimes luck is in your favor.
According to the DTC Summaries manual, which I am attaching, the P0829 code can mean one of two things:
1. ECM torque signal fault
2. Transmission mechanical failure
So my first question would be, how did the dealer determine that your code was not triggered by an ECM (Engine Control Module) torque signal fault, since that is listed as the first suspected cause of P0829?
For proper shift management, the Transmission Control Module (TCM) relies on many signals from several other modules. This information is received by the TCM in both analog and digital forms via the main transmission electrical connector, which is protected by a cylindrical plastic sleeve that is known to develop oil leaks.
Since reported electrical issues are far more common than mechanical issues, I would personally recommend that you have your mechanic check the transmission connector for oil contamination that could interfere with the electrical signals received by the TCM. You mention that Beckers changed the transmission fluid and (pan?) gasket in April, but did they replace the sleeve? And if so, did they get it fully seated?
Have you checked the fluid level in the transmission to confirm it is correct?
I also have to wonder if P0829 was the only DTC present, or if there may have been others stored, such as any U codes that might indicate problems with the CAN (Controller Area Network) communications. Did the dealer happen to mention any other codes???
If it were me, I would not accept the diagnosis that your transmission is "finished" without more diagnosis.
Tough choice, Isoruku. My 2003 xk8 got a rebuild at around 149,000 miles. (same ZF6HP26 transmission). My codes were P0736, 0730, and 0735 - triggering a code and limp home ... and though they are obviously different than your P0829, the possible causes for failure in the documentation is exactly the same - ECM torque signal fault or Transmission mechanical failure.
While I am happy I went with a full rebuild at my high mileage, including reman'd torque converter and friction plates, my indy shop also put in $400 in SONNAX valves that dealt with 'oil pressure regulating) into the valve body in order to correct the error. Trouble is, even after doing all of this, we still had the error during subsequent test drives. They tore the transmission apart trying to find out if they rebuilt it incorrectly, but did not find anything. On a whim, he pulled a valve body from a ZF tranny that was in an s-type and transplanted it into mine. The problem never surfaced again after a week of his 'test driving'. So, he pulled the donor valve body, put those expensive Sonnax valves and springs into it, and installed it back into my transmission. Job done, and it hasn't acted up in the 3 years since.
So, I'm giving you another possible cause for your failure. Remanufactured ZF valve bodies will cost you $800 or so, and there's the labor involved for you to consider as well. I'll tell you it cost me $4,400 in 2012 for this rebuild when it was all said and done, and $2,400 of that was labor.
Here is an update: Just got a call from the independent shop (Becker Service Center) that I drove the Jag to yesterday. (The two mile drive from the Jag dealer was uneventful, with no fault light and no limp mode.)
I gave them a summary of notes I got from everyone, and suggested that they investigate the possibility of a problem stemming from the sleeve that protects the transmission electrical connector, which Don B mentioned.
And the shop did find a bad sleeve and some leakage, so they are going to fix that for $200 and give the car back to me.
But they did caution me that they are not 100% convinced that this will solve the problem, and that I might really have a mechanical failure. They said that the computer was telling them that there is a problem shifting between fifth and sixth gears. If that is a false message and the new sleeve fixes the problem, fine. If not, I will get a new fault light down the road (literally and figuratively) and they can then do a full rebuild.
So I'll post again in a couple of weeks with a new update. And many thanks everyone for the help on this!
I believe it is not unknown for the seal to fail between the valve block and the transmission body. The valves are within the sump and replaceable separately. If the seal (I'm not sure if there is a gasket there or not) fails between adjacent valves, then fluid under pressure gets to the wrong place, as well as the right place and causes rough changes, even no changes. It would be very unusual for the mechanical parts to fail, although I suppose this could happen. Cure is to remove the valves and valve block and reseal.
There may even be something on the internet about this.
The fact that it is nine years old has nothing to do with it. You'll find seventies Jags where the old Borg Warner 65 autoboxes still work, eighties BMW's where the 4HP22 still functions. No, it's not good enough that the box has failed. It's supposed to be a quality car and the gearbox should last 200'000 miles.
The 6 speed Mechatronics auto is a complex unit. Mechatronics means the ECU is combined with the valve body inside the box. What happens is that ZF replaced the paper gasket between the two valve body halves with black sealer. This hardens with age and the high line pressures blow a chunk of it out. With a massive pressure drop, the sensors in the box don't know what's going on but the ECU is making what it will from the info and trying to correct things and it can't - it's rather like the blokes in the bowels of the Titanic with big hoses trying to suck water out. That's the rough shifting. These are not re-buildable boxes, but a really good specialist may be able to isolate the fault to the Mechatronics unit - that's going to be about £1500 fitted but if it cures the problem.......
Are there any auto-transmission shops near you that know all about ZF transmissions ?
Last edited by Fraser Mitchell; 09-02-2015 at 05:56 PM.
That's very good info! But I still have my fingers crossed that Isoruku's problem is electrical, since the DTC Summaries list a problem with the torque signal as the first suspected cause of his fault code, and since his transmission will sometimes operate just fine.
My pre-owned 80k mile, 2005 Jaguar S-Type R has been having the same issues as described in this thread. It has been giving me a "Transmission Fault" message, without any diagnostic code, since I purchased it. When I turn the car off and restart it, the "Transmission Fault" message goes away. It was doing this on and off for about 3 months, typically after some very spirited driving. This led me to start babying the car. I would drive it like I had some sense and obeyed ALL traffic rules. All was good for a while. Then all of a sudden, I started getting the "Transmission Fault" message again...it was happening at the exact same area of road on my commute to work, EVERYDAY now.
On one particular instance, it gave me a check engine light. Now we are getting somewhere. That code was a P0829 (5-6 shift) code. I researched and then cleared the code. The next day, same road, it happened again, but with no code, just a "Transmission Fault" message. I pull over, shut off car and restart it. Transmission Fault message clears.
After thinking it over, based on what the possible causes of the P0829 code means, I decided to drive the car to work, in Sport Mode and leave the shifter in 5. This should make the transmission never go into 6th gear/overdrive. This seemed to work, as when I get past that certain point in my commute (coming off an incline), the vehicle/transmission does not look to go into 6th gear. I manually shift it into 6 and the transmission responds with a very harsh gear change into Overdrive.
This leads me to believe that there is a shift control (solenoid or TCM) malfunction. I gather this as the transmission performs flawlessly (other than the lurching and harsh 5-6 shift) when not at the same part of the road where it normally gives me issues.
I have been looking into a replacement ZF valve body. Am I on the right track?
I had the trans fluid checked for capacity level from a great indie shop. he said it was at proper level and the vehicle showed evidence of the transmission being serviced before. He is unsure of the connector/seal replacement.
08-26-2015, 04:34 PM
Transmission failure - error code P0829
