OK so I am new to this forum but I could use some advice. I am working on fixing a "ghost electrical" issue on my 2003X J8.

I would be driving and the car will go into limp mode and then fully die every time. It will display Gearbox fault most of the time, otherwise it will be ATC not available, TRAC not available. The amber engine light only comes on about after 3-5 of these failures. I cannot restart the car until I wait a minimum of about 2 minutes. Also when I shift the car to Park to restart it, it locks the gear selector for the 2 minutes. Then it restarts fine. I have tried to wait the 2 minutes in neutral but unless I put it in park it will not restart. This issue can happen at any time (has happened about 20 times in the last 2 months).

I have even tried connecting my AutoEnginuity unit and monitor the car live to see what causes it. No issues appear on any of the monitored values on the TCU or the ECU. AutoEnginuity shows P1797 typically as the error. The dealer spent 2 days and cannot figure it out even though it happened when they were testing the car. The only thing they found was a possible brake switch the first time, which they replaced but that was not the problem. I always get a P1797 on the Transmission Control Unit and one in ten times a U2500 on the Antilock Brake System Can. This is irritating since it tends to happen at speeds of 30 mph or more and once I got stuck in the middle lane on a highway which is dangerous.

To date: I have replaced the battery, swapped all the relays from my other 2003 car to this one to isolate any changes of a relay failure, had the throttle body swapped too with a used one because i was getting really high amps reading on the throttle motor (and on the VDP, before I had the AUtoEnginuity to tell me the codes I was getting ATC and TRAC/gearbox fault not available and proved to be the throttle body). Same error code P1797 still came on after the swap.

I had also the dealer reprogram a used TCU and put it on the car to eliminate that possibility, but the same problem came up. They wanted to spend 2-3 days to trace wires but could not guarantee me a resolution (at the tune of 120/hour too). I am about to start tracing the Can wires and check all the ground nuts and TCU/ECU connectors (I have all the diagrams - thank you Gus for your website).

What gets me is the inability to restart the car immediately. By the way it is not the key transponder because the issue comes up with all my 3 keys. I also never got an error from the security module (can it be faulty and not give any codes??). If wire tracing and connectors check out OK should I pay another $160 at my local "*******" to reprogram a Main Computer Module I got on Ebay? Any other ideas???

Other than that the car drives fine and shifts gears fine. Sorry for the lengthy post but I wanted people to have all the info. It took me 2 months of tracing my wife’s 2003 VDP to figure out a short on the door micro switch that would cause her battery drain. I hope it does not take me this long for this issue.

Regards

 

JETJO,

I've moved your tech question from the New Member section to the X308 section where it should get a wider and faster response from members with the same vehicle.

Graham

 

After tracing all the Can Network connectors I found 2 connectors that were bad. That solved part of my problem once I fixed them. I was no longer getting the P1797 but was gettting other errors.
The other bad part that I discovered was the shift gate on the Floor shifter was bad and was causing some of the messages. It appears that all is fixed for now.

 

I am new to the XJR. I acquired a 2001 XJR last month. Today after driving home, I let the car idle a bit. Suddenly, the engine just shut off. The car would not crank or restart. After a few tries, the engine cranked and started and threw a CEL. I read the code. It was a P1797.


I want to check the CAN buss connectors but need to know where the computers/logic modules are located (ECM, TCM, etc.)


Can anyone provide a diagram showing the physical locations for the computers that reside on the CAN buss?


Thanks.

 

I think I found it.