Hey everyone, I'm not entirely sure how to word this although...2 days ago I got my hands on a 2008 XF 2.7D and the car looks absolutely bloody gorgeous inside and outside although the rough part is it's very high mileage (160k motorway miles according to the previous owner). Everything seemed all fine and dandy until this last night and then this morning I'm noticing low battery warning whenever I fire the baby up although it's still running nice and smooth so I've been going on extended drives to hopefully get that battery recharged although tonight after coming home the alarm keeps randomly going off (the sound no flashing lights or whatnot) and I'm curious if it's the alternator that's packed in due to the battery being low, a dud battery (even though the owner said it's a few months old battery or something else and secondly is the low battery the cause of the alarm constantly going off?

I'd genuinely love to hear any feedback/suggestions, this is the 1st time I've actually owned a car as until 2 days ago I've just driven Motability cars and never had this issue and it's slightly upsetting being like a kid at christmas owning such a beautiful vehicle...I'm just worried that this may be the start of a never-ending series of repair jobs and I'm only 2 days in (

 

Use a voltmeter across the battery terminals to read the available voltage with the ignition in the OFF position. There must be a minimum of 12.6 volts available for all the modules to function correctly.

If the voltmeter indicates less than 12.6 volts, charge the battery for five hours at 2 to 5 amps and retest.

Install the Torque app on a smart phone and connect to the ECM/PCM via the OBD port with a Bluetooth interface to read the voltage whilst the engine is running. There should be around 14.2 to 14.7 volts showing initially, and dropping down to around 13.2 after a short run. If not, the alternator may be suspect, or the wiring loom having bad connections.

Should the alternator be the issue, to avoid many of the misadventures of purchasing one from a parts house, have the alternator overhauled by a competent automotive electrical specialist and reinstall it.

Has the vehicle recently passed MoT? Were there any advisories or warnings?

 

Hey NBCat and thanks so much for your reply! Now I'm not going to pretend I can personally do all that although I'll try to contact somebody tomorrow who may have the equipment to do the testing/might try to find a garage near my house on Monday morning to have a look and maybe mention the recommendation from yourself etc?

The vehicle passed it's MOT with no advisories / warnings in Dec 2022 and had only driven around 1,000 miles since due to the previous owner being an elderly man who could no longer drive due to his knees giving in (
Just re-looked at the MOT history and it's not failed an MOT nor had any advisories since 2017 and that was due to tires/break pads which got replaced and new ones was also put on less than 12 months ago

 

-Update-

Took the car to kwik fit for a battery test to try eliminate an easy fix/couldn't find anywhere else open near me & apparently with engine running the battery is being overcharged at 14.92V, now I assume based of what I'm reading it's leaning towards needing to get the alternator looked at?

 

Metalcritter, when was the 15 VDC measured? If you measured it right after starting up the car (or even a few minutes after), that is fairly normal. Jaguar programmed into the charging system a "restoration phase". When you start the car, you suck a lot of energy out of the battery because o fthe starter. Because of this, the car is programmed to shove a lot back into the battery right after starting. so, to do this, it raises the voltage up around 14.5-15.0 VDC to top off the battery. Now, if you had been driving the car for say 20 minutes and you are getting that, then PROBLEM. One of the little quirks that you will learn your kitty has.

 

Hey Thermo, just seen your reply! The 15V was measured within 5minutes of turning on the engine which with what you said fits within the "restoration phase" and would explain that, I could do with a bit of luck on my side right now haha - That's genuinely pretty interesting to learn that so thank you very much for that information and makes complete sense, now I'm back to the drawing board on what potentially could be wrong, I feel like maybe going to an auto-electrician tomorrow would be my next best course of action ? -Goodbye savings- Hahaha

 

Metalcritter, put the battery on a charger. I know the car has a battery monitor in it and well, it does a crappy job of keeping the battery topped up after you leave the car on (engine not running) and getting it back to 100%. I recently had an incident where I used the radio with the engine off to the point that I needed a jump. After that, the car would never recharge the battery right. I even tried charging the battery and it would let the battery fall to a point that it would not start the car. I ended up getting a new battery and solved that issue. Part of what I think was causing it was the person that I bought the car from put in a normal battery, not an AGM. The battery that got pulled out was not that old (under 2 years old) and where I live, the weather is not that bad to kill batteries in that short of time.

 

Metalcritter
A good idea to take it to an auto electrician who can test it under load
and put your mind at rest. I suspect that there is not a great deal wrong
with your Jag