Now that I have my ABS module repaired I am ready to try to sort out the gearbox codes. After driving for 5- 10 minutes Gearbox Fault displays with a yellow warning light and I lose the lower gears, but seem to have 4th and 5th.
the Autoenginuity codes are:
P1797 CAN TCM to ECM Malfunction
P1798 TCM/ Instrument Pack Malfunction
JTIS suggests several possible causes including ECM failure, but no information on how to track down the source of error.
Can someone tell me if I am missing something in the JTIS, or is this where the dealer just replaces everything?
I have removed the TCM and ECM and cleaned all the connections to them. Also checked all the bat. and ground connections. The bat. is new and reads 12.77V.

 

have you tried the diagnostic tree shown in the DTC tables that jaguar uses in the JTIS? That would be my only suggestion, and looking for a common path/component to those communication errors. Maybe its a harness/wiring issue at the transmission?

Try that JTIS first.

 

Thanks Matt, the JTIS kind of left me hanging, not much in the way of diagnostics for p1797. But I did look for a common path and after determining that the CAN BUS wiring was intact between the connecter pins I was left with the impression that the TCU was not communicating with the other modules, and I located a used one with the exact same numbers. It will arrive Tues. and I'll see if there is any change. Of course it may have to be reflashed, whatever that amounts to. I'll probably end up at the dealer before this is all over, but that seems like a defeat to me, not to mention I'm retired and not rolling in money. But no one made me sell the Z3 and buy the Jag.
Ron

 

I'd also checked the JTIS sequence for these codes before coming to the same conclusion as you that the listed 'possible causes' weren't too helpful. Other than a short or open circuit it was all about faulty modules.

The only one you haven't mentioned from the list is INST fault. If this means the Input Shaft Speed Sensor (?), it would be better (less $$) than module problems.

Graham

 

One of the things I have not done is remove the connector from the gearbox, for the simple reason that I don't know how. I can barely touch it, and I can't see how it locks. I don't want to remove the exhaust system just to gain access.
The path of least resistance is to swap the TCM and see what happens. Even the P1798 could be a malfunction of the TCM.
Previous code descriptions were slightly different, so there is apparent confusion in the module communications.

 

It certainly doesn't look easily accessible:

1997 Jaguar XK8 - Transmission Connector.pdf

According to JTIS, rotate the locking lever to release. Probably have to remove the mounting and lower the transmission just to get to it.

Hope the TCM swap fixes it without having to access the connector.

Graham

 

Thanks Graham, now I know how to get it off. I can reach up there, but can't see anything when my hand is there. At least I have a lift and the car is 4' off the ground.

 

The used TCM came today. Ten minutes later I was on the road with no transmission problems. It's nice to know that even old people can diagnose modern car systems, or maybe I was just lucky. Whatever the answer, I'll take it.
The ABS light did flash briefly twice, and the stored codes were the same as I reported a few weeks ago: left front sensor failure and ABS Pump circuit failure, but the stability control light did not come on, and I will probably end up replacing the connecting cable just to be sure that's not the problem.
I would like to thank those of you who responded to my messages, it's a great to know there are others out there ready to help.
Tomorrow I'll take a longer drive and enjoy the mid 80's Georgia weather and the many curves and hills. It will be too hot to paint the house.

 

nice! the tougher of the two problems has been resolved, enjoy it awhile, then dive into the ABS. I'm 99% confident, that if you are getting the pump circuit failure code, the module needs to be repaired. You can still drive it when removed, which should help while waiting for a rebuild (if you send it off). Wait on the LF sensor until you get the module repaired, it may be related.

 

I have a 2000 model year and was unable to drive it with the ABS module disconnected - I took it around the block and began to get a cascading list of errors and gauge cluster problems within the first mile or so...

 

Good to hear the TCM works. That was building up to a serious issue if it hadn't fixed it.

Enjoy the drive.

Graham

 

I have already had the ABS module rebuilt, so I think that is OK.