IanG31

Hi everyone, I'm new to the club and I own a 2006 Jaguar Sovereign 2.7 TDVi, I have an electrical problem with my car. I start it on a morning, the ignition lights go out but after about 5 maybe 10 minutes the battery light comes back on. after about 20 minutes or so it will go back out and everything is fine, but while it is on, especially if I'm on a motorway the gearbox will slip out of 6th and back to 5th and stay there and the gearbox fault message comes up. If I stop the car and turn it off, when I turn it back on the error is cleared, I have had it scanned and the error code P1794 comes up, which I believe is a battery supply malfunction, when the battery light is out, the gearbox problem does not occur, the alternator has been tested and produces 14 volts which I have been told is fine and I have also replaced the drive belt, any pointers to what could be the problem will be well appreciated, Thanks in advance