I have problem with transmission, my transmission lamp light and transmission is in limp home. I wonder where i can find ecu box for transmission and ecu box for engine? And where can i find rotary switch?
And how can i read out dtc codes for transmission?

My car is Jaguar XJ12 6.0 liter year 1993

Many questions

Thanks Fredrik

 

Fredrik: others more knowledgeable than I will respond, but... Before going all crazy with ECUs and rotary switches, I'd disconnect the negative battery terminal for a minute (remembering the radio code if you've got one) and see whether the problem is remedied. This clears the trouble codes and may put your car to rights. Then, you should check the transmission fluid for level and cleanness. There is also, I believe, a fuse that should be checked for the transmission control module. These are all the "easy" things. Beyond that, perhaps the throttle position sensor (TPS), at the base of the throttle body, is a prime suspect for these limp-mode scenarios. I think the jag-lovers website also as a good transmission checklist for just such an occasion you may find helpful. Look under the xj40 book. The good news is that, in my observation, most folks who have this problem find an electrical, rather than mechanical, solution. Good luck! Scott

 

This was posted on 04-06-2008, by "jagtechohio."

The most common reason for the transmission control module to default to "limp home" mode and illuminate the gearbox failure warning is a faulty throttle position sensor.

The throttle position sensor is located on the underside of the throttle body, and its' sliding cotact is rotated by throttle shaft and butterfly opening. That's how the electronically controlled transmission konws when to downshift (unless the full throttle kickdown switch is depresses). That transmission has no mechanical kickdown cable or vacuum modulator.

Normally, failure of the throttle position sensor will cause the 'check engine " light to come on. If it has already been illuminated for a while (uncorrected code 39 is a common example), then you will have to read each code and clear it to read the next one. The TPS may cause limp home without the check engine light, I'm not sure about that but I doubt it.

About the only other problem with these transmissions not shifting corrctly is when water gets inside the Transmission control unit (TCU). It is located behind the right side under-dash panel. There are points of water ingress on the 1993 and 1994 cars that cause all sorts of problems, and this is one of them. There is an old factory bulletin that describes the installation of a water shield for the TCU to help with this problem. It doesn't happen often, but was common enough to inspire a factory band aid.

The only real knock against '93-'94 XJ6 is engine oil burning on start-up from oil leaking past the valve stem seals. Those cars, and their successors which used the same transmission and similar engine, are nearly indestructible. All of the problems are minor, only the expense and scarcity of some of the components is sometimes a nuisance.

This thread has helped me quite it. To read along without having to start a new thread go here:

https://www.jaguarforums.com/forum/s...ead.php?t=2500

Enjoy the ride!

 

I try disconnect grond from battery and test and lamp flash is gone but when i try drive lamp flash is back. Anyone test diagnos interface for this car on ther year model? I think dtc codes for transmission. No check engine lamp flash and it work start car in park and neutral. I cant find relay for transmission and where is ratary switch?

 

I find solution, in transmission control module i solder all regulators and all pins and after this is lamp flash gone.

 

Car work about 2-3 weeks and lamp flash again and in limp home...

 

The only diagnostic computer that I know of that will communicate with your ECM,TCM,ABS is the Jaguar PDU. It is a really old early 90s computer that was never updated to the WDS or IDS. Call around to some Jaguar dealers to see if they still have the PDU.

bob gauff