1. Background: 2002 XJR, only about 60K miles on odometer. ABS/TRAC Not Available has been showing, with rare exception, since October 2019. Car has had 3 or 4 prior owners from new, so I don’t know the history of the transmission (whether original, ever been serviced, etc.). Car has been in “lockdown mode” for the past 2 months with only three short trips (each in the 10 – 20 mile range) spaced 2-3 weeks apart during that time. Car was last driven 15 days ago and then parked in the garage until yesterday morning. I realize that having the car just sit for weeks is not ideal.

2. Problem. Yesterday morning I started the car from cold after it was parked in the garage for 2 weeks. In addition to the usual (ABS/TRAC) warning, “Transmission Fault” was also displayed. I have never seen the “Transmission Fault” warning before during several years of ownership of this car. So I’m sitting behind the wheel in a state of shock, it’s still early – coffee hasn’t yet kicked in and I’m seeing $$$ signs flashing in my mind. When I moved the shifter into “D” (with foot on the brake, of course) the car lurched forward slightly, then moving the shifter into “R” the car predictably lurched backwards slightly. After about 5 more minutes of idling in the garage I shut the engine off.

About an hour later, car still parked in the garage with the engine off, while I’m standing about 12 feet from the hood ornament I heard a click that seemed to come from the direction of the car. I decided to restart the engine, and this time the “Transmission Fault” did not appear (the usual ABS/TRAC Not Available was the only warning shown). I shifted all the way through the J-gate and back to “P” normally. After idling while still parked in the garage I shut the engine off. This morning when I started the car again there was no “Transmission Fault” warning and shifting through the J-gate was normal. Just to be clear, the car has not left the garage since I saw the Transmission Fault warning yesterday morning.

3. Question – what to do? Was the appearance of the “Transmission Fault” due to the car being left unused for weeks in a humid/moist atmosphere (coastal community sheltered by tall trees and frequent rain during recent weeks)? Is it OK to use the car as normal and simply react to any problems that might develop, or should I take some steps, e.g., diagnosis, before driving it?

BTW, I bought an inexpensive OBD-II scanner online a few years ago but found it of little value and no longer have access to it. Also, I prefer not to take the car to a mechanic since there is no obvious problem with the transmission as of today. I tried to include a fair amount of detail in the event that some of the information might be diagnostic. Any advice from the experts would be much appreciated. Thank you.

 

The transmission fault appearance would indicate a weak battery from sitting. I would take it to an auto parts store and have the battery load tested. It is losing voltage while sitting causing the fault. I will do a little research and get back to you on the abs/trac not available but that is usually a battery fault also, but since you have had it for awhile it might be something else.

 

+1 on testing the battery.

The battery should have a minimum of 12.6 volts when checked across the terminals with a voltmeter when the ignition is in the OFF position. If the battery has less than 12.6 volts, charge it for 6 to 8 hours at 2 to 5 amps then retest. If the battery still has less than 12.6 volts, it's suspect and should be replaced.

If the vehicle isn't driven for extended periods, the battery should be connected to a maintainer.

The ABS/Trac Fault may be caused by melted solder connections on the ABS module circuit board.

 

Try to get ALL the modules read for DTCs and you will likely find LOW VOLTAGE in many of them.

There might be other reasons for the fault(s) but the battery should be first.

 

Today I got a measurement of 12.1 Volts using a multimeter across the battery terminals with the ignition off (only the trunk interior illumination lights ON). I don’t have any other equipment to test, charge or maintain the battery. If I start the engine and "Transmission Fault" is not displayed today and if I then drive the car on the highway to charge the battery (lights off and with minimal use of accessories) and then return home without shutting off the engine, how likely is it to develop a problem, e.g., going into Limp Home Mode, while driving? Thanks

Also, can anyone with experience recommend equipment to test and maintain the battery -- simple to use and without spending a ton of money.

 

Replying to NBCat. Not surprisingly the voltage reading (12.1) is obviously too low but I don't have a battery charger. If I can drive the car on the highway with lights off and minimal accessories used, and assuming the battery and alternator are good, about how long would it take to re-charge the battery -- the equivalent of charging for 6 to 8 hours at 2 to 5 amps -- before I retest the voltage across the battery terminals? I last had the battery checked professionally October 2019 and the result was "100%", but of course, while the car is sitting the battery could deteriorate rapidly. Thanks.

 

While the car is sitting, the battery does not "deteriorate" but is being slowly discharged by the car's electronics (normal thing on our Jaguars). However, if the battery is left at, say, 12.1 volts or lower for longer periods of time, then it will start deteriorating (irreversibly losing its capacity).

Before you drive the car to charge the battery, check the voltage on the battery while the car is idling. If you get around 14 volts, your alternator is good. Starting from the recorded 12.1 volts, you will need to drive the car probably for some 3-4 hours to get it fully charged. After the drive (and the engine switched off), don't measure the battery voltage immediately as it will give you a false high reading but check it after about half an hour of the car sitting. If fully charged, the battery will show about 12.6 volts.

Otherwise, if the car is not used almost every day but often parked for more than a week, you need to get either an automatic battery charger (charge + maintain) or a battery tender which just maintains the battery meaning you would need to connect it to the battery immediately at the start of the longer parked period. The alternative to this is to simply disconnect the battery.

 

Yes, irreversible deterioration of the battery while sitting with the battery having already been discharged due to infrequent use of the car – that’s what I was concerned about. Don’t you hate it when you turn the key and it doesn’t even crank! BTW, this car has never failed to start during my ownership, even with an old battery and lack of use during the pandemic.

Drove the car for an hour this morning at an average speed of about 40 mph, in “D”. Shifted flawlessly and no sign of the Transmission Fault message. Tested the battery terminal voltage when I got back with engine at idle (about 650 rpm on the tach) – 13.95 V -- remarkably close to the target value of “about 14” V. Shut off the engine and tested the battery terminal voltage 35 minutes later with the ignition OFF – 12.4 V. So, it seems the battery (starting at 12.1 V) is already more than half way to the target voltage of 12.6 V after just one fairly short trip, and I’ll be driving the car again tomorrow. The alternator is good, and apparently the battery is still good despite it's age and the lack of use. Nevertheless, since this battery is more than six (6) years old it’s probably best to replace it soon. Thanks again to those who got back to me on this.