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Hi,

I have a 2010 XF 3.0 V6 petrol and have encountered an occasional problem with starting. My normal procedure to start the engine is to press the Stop/Start button, wait for the vents to open fully, then press the Stop/Start button again whilst at the same time pressing the brake pedal. 99% of the time this works but just occasionally the starter doesn't operate and the vents close down again as if the ignition is being turned off.

I have noticed that, when this happens, the brake pedal seems very hard and doesn't depress very much, whereas it does go down a little way in the event of a successful start. I think the failure to start also seems to be linked to the vehicle not being used for a few days.

So far, I have found that I can get the engine to start by using the key fob to lock the car and then unlock it again. However, on the most recent occasion I had to repeat this process several times before it worked, so I am just wondering if the problem is getting worse.

A Google search brought up a mention of this problem on a US Jaguar forum on which others were posting that they had suffered a similar problem. One person suggested that the problem is caused by the brake pedal pressure sensor switch.

Does anyone have any thoughts, please?

Hi,
Maybe I am just not as patient as you but when I start my XF I never wait for the vents I just put my foot on the brake and press the Start/Stop button.
Two thoughts.
Is this a timing issue and your ‘two step’ use of the Start/Stop button is confusing the system into thinking you are actually cancelling the start operation?
Is your battery failing as the event is happening after several days of sitting idle?

Rod

Hi Rod,

Many thanks for your reply. I may be wrong, but I don't think my "two step" starting procedure is the problem because it always works except on rare occasions.

I must admit that I had thought it might be a battery problem - especially as I have a suspicion that the battery is still the original factory-fitted one, so it's now getting on for 9 years old - but has only done about 24,000 miles.

The one factor which is still puzzling me is the brake pedal. I now know when I'm going to have a starting problem because the brake pedal is very hard and doesn't really depress at all whereas it does depress by a noticeable amount when the car starts properly. Is there any way that a duff battery could cause this, I wonder? Is there some connection between this and the brake pedal pressure sensor switch, in that low battery output is perhaps inhibiting the switch?

Hi,

I tried your 'two stage' start procedure this morning and had no issue so I guess that's not the problem.

I have no idea about the brake pressure observation. Maybe someone more knowledgeable can comment.

At nine years old your battery is likely to be a prime suspect. There's lots of advice on battery replacement on the Forum for you to research.

Rod

Hi Rod,

Yes, you're probably right about the battery. I will investigate that further.

Thank you very much for your time and thoughts on this.

Regards,

Jim

You're right about battery -- nine years is really pushing it and a tribute to whatever manufacturer Jaguar has used for OEM if indeed it's OEM which I'd be surprised at. Six years with a Bosch/Varta/Yuesa 5 year warranty series is
pushing it. So the car must've had at least one battery change out in its lime IMO

The brake pedal going down a little is correct for when the engine starts as the brake system pressures up with the ABS pump coming on and vacuum building up in the servo.
Get a hydroscopic test done of the brake fluid -- 1% is OK, 2% means watchit schedule change, 3% or more means flush thru and change out all brake fluid for new

Hi Richard,

Many thanks for your reply. The only reason I'm guessing the battery might be original is that it has a "Jaguar" stamp on it. However, the previous owner of the car (who had it from new) did use Jaguar main dealers for servicing, so that might explain it. However, I do have experience with a very long-lived battery in a previous vehicle, an MG ZS180 which I bought from new in 2003 and sold in 2014, still with the original factory-fitted battery - which was still working perfectly. But that's the exception to the rule, I'm quite sure!

Thank you for the suggestion about brake fluid - I hadn't thought of that. I will get it checked.

Regards, Jim