Jaguar Repair Questions? Ask a Mechanic for Answers ASAP
This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default.
This will reset all the systems on the car and you may need the radio security code to get it going again, and ensure that the keys are in your hand when you re-connect the battery as the car may lock and turn on the alarm
also a good idea to charge the battery overnight as a failed or discharged battery will also produce this sort of fault