Stop start

[Firefighter]

Jaguar XF RSport 180,2018 .Stop start not working,No fault or warning light showing,Battery reading on tester reads 12.4 volts.not switched off on console

Anyone any indication what the problem could be,
Paul.

[Trooper2142]

When i bought my XF in September last year, the Stop/Start wasn't working and they checked the Battery and it was 75% charged and seemingly the Battery has to be at least 85% for the Stop/Start to work.

I kept asking the Ford Garage to get this sorted, and i took the car in on the 9th of December and they charged the Battery over night and the Stop/Start still didn't work.

So they fitted a New Battery which has a Higher Rating 95 AH/ 950 A as the original was 80AH/ 800A and the Stop/Start is working as it should, and starts working within 2 or 3 miles of leaving my house.

Regards Tom.

[PeteL]

Firefighter, I bought my XF a year ago and ever since I've had the car the stop/start has only worked when the engine is fully up to temp. and Ive been driving for a while. Someone on here will maybe tell me that there's something wrong with it, but quite honestly I would prefer to be able to switch it off permanently. I find them a nuisance , but I hope you get yours sorted. I'm sorry I can't give you an answer on fixing it, but that's my experience as a first time owner.

Regards Pete

[Big John]

Here is a thought. Having left my Sportbrake sitting during lockdown I suffered a totally flat battery, which led to a software crash preventing the rear doors opening. (see other thread)

What has this to do with Stop / Start? Well I have been doing a fair bit of reading and they are linked. The XF has several dozen computers all talking over a network. One video I saw showed that with the ignition on and the engine not running the power drain was around 12A that is 12Amps not a voltage of 12 v!  Computers love to eat current.

That explains the dual batteries used for the S/S. As I found out with my flat battery; the myriad of computers and the network are sensitive to low voltages. Although unlikely to actually damage a module (computer) physically, a low voltage can corupt the software. That is why the small battery is there. When the engine is stopped all of the "computers" are fed by this "Fresh" battery as long as its voltage remains within limits. If it drops, rather than compromising the network stability, the car will restart, using the main battery for the starter (and non sensitive things like fans with the engine off because these things are not really damaged by low voltage particulalry when the starter is working) .

So what is my point? If your S/S is not working it is probably because one or both of the batteries is not charged enough to ensure the car can re-start. That means your battery voltage maybe getting lower and lower due to age, short journeys, heavy power loads like lights / Heater / Air-con, Flooded Cell rather than AGM battery etc. So the non-functioning of the S/S should alert you to a low battery charge and if that means when you turn off the engine, and the alternator output is gone, but you still have the lights on and the heater fan or whatever the voltage MAY drop low enough to cause the sort of problems I had, next time you return to the car.

Welcome thoughts and other ideas but I think if S/S is not working you can save yourself all sorts of grief with a new battery (batteries) and a CTek smart charger to keep the batteries fully charged. If it annoys you, turn it off as part of your start-up routine, but maybe you are also turning off an early warning system that could save you lots of money.

Having lit the blue touch paper.........

🙂