2002 X Type - Gearbox Fault
 

My 2002 X Type gets an error message, gearbox fault, abs light, brake light and speed odometer stops working. Car goes into limp mode. Usually happens when sitting at a red light or just starting from a stop. If the ambient temperature is 60 or lower, the car starts and drives fine. The temperature gauge reads normal. Drove my son to school and back home with no issues, shut the car off and let it sit for 15 minutes, turn the key on without starting and displays gearbox fault, abs light on, brake light on. Start the car and get the same error messages. If the car sits and cools down for a few hours the error messages clear. Can start the car in the driveway, running fine, let it sit running for 15 minutes and get gearbox fault, abs light on and brake light. If the ambient temperature is cool 50 or lower, car cools down for 1 or 2 hours, it will then start up fine. If ambient temperature is 75 or higher, get a constant gearbox fault, even with 1st startup for the day. Had the codes cleared and read P1799, TCM is bad. I read about water getting to this module, so I removed it and the circuit board to find no signs of water. The module looks like new, but I guess could be bad. It does not make sense that the ambient temperature would affect the TCM working correctly. Maybe a sensor or thermostat is bad? Has anyone seen this particular problem before or any ideas what might be the problem. Any technical advice would be greatly appreciated.

Rick
2002 X Type 2.5

The very first thing to verify when you get random and/or multiple faults flagged is the battery voltage.How old is the battery? I assume that this car is used regularly? Modern batteries, if over 5 years old, are suspect. The X-Type is not the electronic marvel that the XK, F-Type and other more modern models are but like these, it does require full battery voltage to avoid these issues. You may have another fault, but the battery is the first suspect (and even if the battery is recent, note that new batteries are almost NEVER fully charged off the shelf, despite what the clerk tells you - and if the battery does not start its service life with a full charge, it may never get fully charged - depending on the usage pattern).

Last week I put a brand new battery in a 2007 XK; the store clerk not only assured me that it was fully charged, but he brought out a hand-held instrument to check the voltage....12.7 volts, "Battery GOOD" said the read -out. Well, the battery should have shown more than 13 volts....I took the battery home and put it on my CTEK battery maintainer. It was 36 hours, yes, 36 hours before the battery was at full charge. Only then did it go into the marvellous but voltage-hungry beauty known as the XK.

I agree with sov211,

Though before you run out and buy a shiny new battery; Clean your battery terminals. Remove both negative and positive leads clean them with a wire brush, sandpaper, or better yet one of these:

https://cimg4.ibsrv.net/gimg/www.jag...39032a9a13.jpg





I've kept one of these in my toolbox for over 30-years.

P1799 CAN TCM/ABS Circuit Malfunction Code

Check wiring for chaffing, breaks, connections on tcm, ecu, abs sensors, transmission, and parking brake (on position) sensor for corrosion/grease/oil contamination.
The temperature changes in frequency lead me to suspect connection problem. Cooler (contracts) no problem, hot (expansion) constant problem.

2002 X-Type - Gearbox Fault
 

Thanks for the recommendations,all good input. The battery is an Interstate brand and approximately 2 years old. I cleaned the battery terminals and posts.Battery voltage is 13vdc and 15 volts with engine running or alternator voltage. I checked all visible wires, connectors, removing, inspecting and re-seating, along with front ABS sensor connectors. I still have more to check and will do so over the next few days. Will have the battery tested tomorrow at the Interstate Battery store. Ran the car today and same problem. Faults in the driveway after engine gets hot. Opened the hood for 30 minutes with car off, started car and faults cleared. One thing I did not mention, A/C compressor failed months back and pulley bearing making a loud noise. I by passed the A/C pulley with a shorter drive belt and worked fine for a month or two. Not sure if this has something to do with the problem, so thought I should mention it.

Thanks again for the help!

Rick

2002 X Type 2.5

I have $30 battery from junk yard in my X. I picked one with 2019 label on it. Works fine.

I'm so happy for you - that should solve the problem....