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Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 22907
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My 2010 Jaguar XF has a battery drain issue. I've monitored

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My 2010 Jaguar XF has a battery drain issue. I've monitored the readings and within 10 min of engine off it can lose 0.4v, and go on to lose 0.6v per night. Does this suggest a faulty Battery Monitoring System module as it's discharging so quickly in a very short space of time?
Hello Graham I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable. A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next. Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking.. Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright. if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge
Customer: replied 2 years ago.
Hi Matt
I appreciate your general advice but I'm in the middle of doing most of this already. I've got a multimeter testing the regular drop in volts and I'm ordering a clamp meter for the amps. the battery is only a couple of months old, but there was nothing wrong with the old one, it's just at 5 years it was better to change it to eliminate it from the possible problems list (it was changed using a spare battery to avoid KAM damage).
What I really need is advice specific to the XF and its known battery drain problems. Have you worked on these? So far I've tried fuses on bluetooth, car interior lighting, DVD player (SatNav only), towing accessories (none fitted) and seat adjusters. Could you help me with the following please?
1) Do you know if the BMS can still be malfunctioning if it is still sending warnings to the info screen to shut down unless car started, which is what it's supposed to do? Would this help explain the measurable loss overnight of up to 100Ah/0.6v? I can regularly measure the drop in volts, but I don't have the means to measure the Ah loss regularly. As you'll know, the BMS can reduce the battery voltage and then charge it up again to maintain it. Do you know if they can malfunction while doing this? If a previous owner has jump started it using the neg earth lead instead of the spare tyre tie-down bracket, could this explain a malfunction like this?
2) Do you know of Keyless Go modules malfunctioning that could explain the overnight drop in battery power? If I pull a fuse on the Keyless Go system, will it still allow me to operate it using key fob remote control + insertion in key slot, like a normal non-keyless go car, while I evaluate any difference in battery performance? The fuse would have to be removed after system power-down (20min+) using the latched door method, wouldn't it?
3) Have you experience of the infotainment system needing a software update or reflash to override errors that can result in it not powering down modules?
4) The whole charging/generator system was checked by a mechanic who said it was fine. A voltage reading with engine running says about 14.6v, which would confirm this, wouldn't it?
5) Is there anything else you could suggest based on your knowledge of XF's?Thanks a lot
It's a 2010 XF-S 275PS 3.0d.
Hello Graham OK thanks for the detailed replypulling the keyless go fuse should still allow the vehicle to be operated with the regular keyso I'd agree that this is a worthwhile test to try I'd suggest purchasing a simple current clamp ( which it sounds liek you're doing) so you can do the fuse out testAlso if the car is left unlocked in the garage then the infotainment will constantly be scanning for bluetooth devices as its only goes to 'sleep' once the car is locked Also there is a software update for the infotainment systemas the early software versions could sometimes wake up unexpectedly and then drain the battery If you have your VIN number to hand you can contact your local Jag dealer and they can tell you if the TSB / software update has been applied
Customer: replied 2 years ago.
Hi Matt
Unfortunately the remote key fob won't unlock the doors if the keyless go system is deactivated by pulling the fuse. Does this suggest that they share the same frequency and signal method, or do you think because they can't be worked independently this is indicative of a fault? I presume it would still work in the key fob slot under the dash on the driver's side, but you would then have to have gained entry by the metal key on the passenger side handle- this isn't a practical alternative for normal car operation while I assess the effect on the battery drain of a deactivated keyless go system. What do you think?Did you have any advice on the BMS as above?
HelloI was thinking that you would use the metal key to unlock the car and just use the meter to check the battery drain while the car is in this mode as yes its not practical to use the car in this way I meant just to try it for diagnostics
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Customer: replied 2 years ago.
I've asked you several times for advice on the BMS but you haven't answered this key part of my question. Okay, I'll credit you as satisfactory but I won't be using this service again. Thanks for your other advice though.