I had an odd experience today with my 2008 Vanden Plas (less than 60,000 miles on the odometer). It was a cold day here in Nova Scotia and at this time of year our roads have lots of frost heaves and pot holes. When I went over a bump (I could hear and feel it) at about 40 mi/hr two yellow warning messages lit up on the instrument cluster "cruise not available" and "gear box fault". I continued to drive and the car shifted smoothly. I noticed I couldn't engage the 'sport' mode by pressing the button next to the shifter, but other than that the car ran fine. When I got to my destination I turned the car off for a minute and then turned it back on, and voila - these warnings were gone. On the drive home I engaged and disengaged the 'sport' mode and it worked fine. The fault warning hasn't reappeared, but I'm left wondering if the bump in the road and a loose wire/sensor caused this?

Someone mentioned that even when these warning lights go out, there should be a code stored, so I used my Jaguar Code Reader and ran a manual check on the Transmission Control Module. It had one code stored: "P1974 Batter Supply Malfunction". Do I have a short somewhere, or do I possibly just have a weak battery (it is five years old and this has been an exceptionally cold winter). I assume the TCM, like the ECM checks the voltage it is receiving at the start of an ignition cycle, and if the battery is weak? A few years ago I had the dreaded "Park Brake Failure" light come on intermittently on my wife's XJ8. A new battery fixed that problem.