So 2 nights ago the car lock me out when I get out from work while I was warming the car up(I warmed up my car everyday before drive so please don't flak me...). Since it's a 2005 and it still running the stock Jaguar battery I decide to change it out after being tested at the borderline healthy voltage and it happen again last night the same thing. When it happen the whole dash light up like Christmas tree and all the fault code come up like transmission fault, low coolant warning, DSC not available, park brake fault, center console for the climate control show no connection meassage and consult dealer blah blah blah etc, and from this awesome forum reading for the past year I figure out it's the insufficient amperage from dying battery that cause this. Only thing that baffles me that from various member's post that when this happen it usually follow suit with restricted performance but mine is still operated with full power and drives like normal despite all the warning. I did turn off and restart the car again when it happen and the red light is lighted up and the check engine sign is on while the rest of the light(battery light, the amber light) and warning word on the odo is gone.

Today all the code is cleared up and and I unplug all the connector and clean the connection with electrical contact cleaner. Also manage to go into the diagnostic menu once this morning to check parameter and later on I can't get into it anymore.

Now the real question is, while this morning in the diagnostic menu I set it at the voltage monitoring mode and while driving with just radio on and everything else off(no light, ac etc) the voltage is just fluctuate around 13.9-14.1 volt. Is this indication that the alternator is on the way out too? All the car I've been working on usually have the voltage hovering around 14.5-14.7 with healthy alternator. From all the yahoo search and it seems that healthy charging system is usually at the minimum should be running at 14.4volts and maxed out at 14.7volts.

Now I'm eyeing on Ebay for alternator and have an alternator pick out ready to buy depending on the response here to let me know if my alternator is good or not. I'm looking at the 140amp unit and was wondering what is the stock 2005 XJR alternator's amperage rating is? Is it 120amp like many seller is selling? The alternator shape looks like some unit on some Ford cars and I'm suspecting it's a 130amp unit for stock 2005 XJR.

Thanks for reading thru all my fumble and I really appreciate all the info and insight I can get.

 

As you've found out, bad wiring connections are the bane of life with a modern car. Other thing worth checking are the earthing points (USA=grounds). There are three at the front of the car, behind the headlamps. Take off the black cover and have a look at them. While you're there, also check the brake line running along the top, it can corrode badly.

I don't think your alternator is failing, the voltage seems OK to me, bearing mind the car has a load management system. How many miles on the car ?

 

The car have about 95k miles on it now. I'll check the grounding point again tommorrow. It happen again 2 days in a row after the battery being change and after raining. Now for the pass 2 days it is not raining and it is fine and normal. I have a hunch that it is high humidity related and I did check the trunk and there is no water in there.

Time to do some wire and connector checking tommorrow.

 

https://www.jaguarforums.com/forum/x...as-tree-10403/

Based on this thread today I went under the dash and unplug and spray electrical cleaner in all the connection as a preventative procedure and see how it'll hold up.