My 99 XJ8 has 85000 miles on it. About 5000 miles ago I changed the transmission fluid and did the upgraded main pressure valve. I used Lifeguard 5 transmission oil. All of this to try and extend the life of the transmission but it seems was all a waste. Today I first got the P0743 code with a transmission fault yellow light. The car wouldn't move, as if it was in neutral. After shutting off the engine and restarting the car I was able to get about halfway home before the same thing happened and again was able to reset it. Once I got home first thing I did was check my voltage. It was 11.8 Volts. So I replaced the battery as it was getting old anyways. New one measured 12.6, so I reset both the check engine light and held the positive cable to the frame to reset the transmission computer. Went for a test drive and this time felt a nice clunk that I have not felt before and am now getting the P1733. The car will continue to drive now, but I noticed the engine RPM is idling higher than normal and it cruises faster with no gas than before.

Please tell me there might be something else going on here. Maybe a sensor? Or am I really going to have to spend 3K here on a new transmission at 85K miles! That is going to be hard to justify. I really thought I would get 100K before this would creep up.

I don't know if this is related, but just before this happened I jacked up the rear of the car to take a look at the U-joints as I heard a clunk from the back of the car a few weeks ago. I don't think this clunk was transmission related but maybe it was who knows at this point.

 

So, there could be good news on this front...there could be bad...but lets see.
The 734 and 1733 could be related on a common issue, ...low on fluid...which we all hope is the answer and the rest of what I typed is irrelevant.

0734 is tied to a few items...faulty PCM, ECM, TCM or could be a bad shift solenoid...thus causing a failure to shift condition for no apparent reason.
1733 is a shift fault between 3-4 gear.
So you can see a commonality there.
A deep diagnostic tool would be seriously recommended and worth doing (CYA piece of mind, but no guarantee) and you not being stuck on the side of the highway.
You'll want to check the shift linkage for worn/stretched cabling and check the electrical connection on the shift indicator to include the indicator itself. The detail I posted are from the XK8, but I do believe they are the same.

Other possible issues:
Mechanical failure inside transmission
Internal blockage inside transmission main control
Faulty transmission control module

 

Thanks so much for the response. I spent the afternoon yesterday troubleshooting the things you suggested. I dissembled the shifter and couldn't find anything that looked wrong in there. Also looked underneath the car where it connects up and it looked OK. When i shift it feels fine and the D lights up. Also I did a few test drives and tried shifting in manual and every time I go from third to forth it goes into neutral with a "Transmission Fault" annunciation. So I suspect the linkage is ok?

Next since the transmission was warm I jacked it up with engine running, shifted through the gears and popped open the fill plug. I was surprised to see quite a bit of fluid come out. Id say I lost almost half a pint before it went to the steady light stream where your suppose to cap it. This was with the case around 40C in temp. So if anything it seems it might have been slightly overfilled?

I cleaned the ABS sensors just in case it was some bad sensor. I do see another two sensors on the rear wheels. Guessing this is a speed sensor gear? I didn't investigate further but I wonder if that might cause problems?

I'm thinking of dropping the pan next to see what I find. Does anyone happen to know which valves control the switching from third to forth gear?

Also, the car shifts just fine until it goes from third to forth. It seems to me (and I could be wrong here) that it is shifting quite early. Anyways what speeds should it shift from and could this be the classic A drum failure if the other gears shift fine?

One last question, what is a "deep diagnostic tool?:

Thanks for any help guys.

 

A deep diagnostic tool is a fancy name for a Technicians scan tool that can read deeper than a standard scan tool. They can do live diagnostic runs and function items in the transmission with them to check for function/failure.

As for your scenario, there's a ton of videos on Youtube about this to include rebuilding the valve body to the whole transmission. Just go there and type in Jaguar zf5hp24 P073 and you'll be rich with info.

Here's one for the "A" drum, this guy is good at giving you a description of what the vehicle will do if you have a certain problem and has a number of videos.

 

well I figured out the problem. Transmission needed a rebuild. I dropped it down and found a blown A and B clutch see damage in photos. I decided to replace the lower front valve body due to wear, and used the updated ZF main pressure valve. Also replace all O rings inside the transmission along with the F piston which was slightly worn. Anyone scared of this job, really it isn’t as scary as it sounds just watch all the YouTube videos by Gary and also get the complete ZF manual and go slow. I made my own compression tools out of PVC pipes and C clamps. A bit clumsy but worked. I only replaced the A clutch pack. The others seemed fine (80K miles).


Be careful not to get these mixed up









Hub blown off of the B clutch

Blown out A drum

 

Thanks for posting JB, definitely a good reference for someone in the future. Nice little tidbits on using "non-specified" tools.