Renos

My 2014 XF start stop used to work; now it works ONCE every time I start the car , usually at the first stop. If the stop is prolonged , say over 45seconds , then whole AUdio System blanks out and it takes 10-15sec to work again. An independent electrical guy told it the Gateway START STOP module that is at fault . But the garage cannot rectify it Renos

I had both batteries replaced , car checked by the Jag garage but still have the follwoing problem. The START/STOP function works the first time the car is stopped after starting . Then it never works again. If I switch off the car and then restart , it will function again the first time I stop. The garage will not recognise the proble , but just give me excuses about condiottions etc