I think the typical response is , what is the battery voltage at rest car off. How old is the battery . Start there.

 

Definitely - suspect the battery first! It may seem contrary to common sense that a failing battery would start the fans going, but battery failure in these cars - and that means not only a battery at the end of its life, but a battery that has not been kept fully charged (and this can happen despite being used almost daily if the runs are short) - produces a great variety of electronic issues - warning lights, outside lights coming on, wipers moving, top not latching, touchscreen freezing, windows and seats not behaving...the list is very long. In virtually every case there is nothing wrong with the component. The problem is that the module which controls the component is not receiving full voltage - and bizarrely, this means that components you have not switched on, can become active.
So, the battery first. If it is more than 4-5 years old, replace it (and be aware that new batteries are NOT fully charged in most cases); the best advice for the XK models: obtain a CTEK battery maintainer and use it when the car is not actually in use. Photo of a resting XK (note the CTEK charger on the floor):

 

 

That's way low, it should be at 12.6 minimum. A good long charge on a REAL charger and not a maintainer or trickle charger MAY wake it up, but you will probably need to replace it soonish.

 

You didn't mention how old the battery is. Also while you have it at autozone have them do a Load Test also. That should give you an indication of the battery. I would say that at 11.58V your battery is bad. As mentioned it should be 12.6 volts at rest.

 

 

You should be ashamed of yourself that your garage is so much cleaner/neater than mine!

 

 

 

 

 

The photo was taken from a select angle. A full garage shot would have displayed my messy inner self. But the Jags are always clean.

 

 

That isn't promising at all. Did you have on any lights, stereo, seat heat/steering wheel heat, stuff like that?
13.3 not great, but also far from good. Me, I'd turn on every power-draining thing in the car and try your test again. The more info, the better.
Again, doesn't seem promising so far.

 

 

Yes, the alternator voltage output is too low. If you are going to work on this yourself, look at the repair manual, charging system info, section 414-00. It suggests checking fuse 5 in the rear junction box, seeing what DTC was logged, and making sure the associated wiring harness is not damaged. Look for a loose ground cable or a loose alternator output cable, for example.

It would be a good idea to follow the troubleshooting tree before deciding to replace the alternator. Good luck.

 

 

Hellow my name is Danielnat. Wery capable article! Thx