Hi, my car is a 2004 XJR and I`ll give a brief history of the issue.

It started when weather became cold, lower than ~0-5 celcius. I was driving, all was ok, however when I stopped I got multiple fault lamps and a kick from the gearbox, it went to safe mode or something, the engine stopped soon. The car failed to start and the voltage was around 8-9 v. After jump starting everything was fine, all errors cleared.

Same scenario repeated several days later. I took the car to a service and they couldn`t find the reason, only presuming it could be the alternator, however, I`ve heard that it`s already been replaced on my car not so long ago.

Since then I`ve been monitoring voltage every time I drive the car, trying to figure out any tendencies in it and shutting off lights/music/conditioner any time it goes low.

When I start the car the voltage sits around 13.5-14.0v, it lowers to 11.6-12.4 when driving with lights, etc and tends to be lower when I stop then sometimes going up to 13.5 under even slight throttle. I can`t say all this happens all the time, sometimes everything is ok.

One time when driving slowly in a traffic jam I noticed that I started getting DSC light when braking to 0-10km.h and it was disappearing the moment I slightly pressed throttle. Before I managed to switch off major electronic I also got a gearbox fault error. However after switching off xenons and air con I was able to continue driving, otherwise the engine would stall.

I have zero knowledge in electrics, but my presumptions would be:
1. It has something to do with outside air temp
2. I don`t think it`s the battery as it`s almost new
3. I was told that alternator was replaced after previous owner experienced same issues
4. Perhaps when voltage is 13-14 it means that alternator is charging the battery and powering all the electrics and when it goes down to 11.5-12v it`s just the battery working and the car displays and stalls when the battery is empty.

I am not 100% sure but I believe (and hope) it`s some kind of bug/glitch, not just an alternator failure.

Sorry for long post, please share your thoughts and any similar experiences, thanks!

 

A lot of peculiar "happenings" with electrics have been linked to bad earths, (US=grounds). There are three that are known to give trouble, all situated at the front on a panel by the radiator. Remove the black top cover over the radiator front and you can see them, all exposed to salt spray and damp. Two on the left looking towards the rear of the car, and one on the right. Don't ask me why Jaguar decided to put them there !!

You have to be exceedingly cautious if undoing the nut securing the leads attached to the earth, as in some cases the aluminium stud of the earth point has been found to be corroded through so badly it just crumbles away when undoing the nut. They seemed OK on my car when I last looked so I sprayed some maintenance/anticorrosion spray on them, and all has been OK so far, and I got through the last UK winter.

However, having the cover off, I could also see the brake line to the nearside front wheel, (US=offside). This was starting to corrode from salt and rain, (car on only 35k miles), so I had to spray stuff on this line to stop further action.

Of course it may not be the earths, I am just putting a hypothesis forward that was outlined by the head of a Jaguar independent shop at an X350 forum I attended this year run by the UK Jaguar Enthusiasts Club at the Jaguar works.

 

I will take door #4 Bob!!

Who "told" You the alternator was changed. Is there a receipt. Does it have a warranty>

 

During over 20 years as a shop mechanic for a pipeline company with a big fleet; we found that rebuilt stuff gave us a lot of problems. The rebuilders try to only do what will get it out the door and last for a while. That cost us big time. We went to remanufactured. Higher cost up front but less changing of components.
The regulator may be going bad or diodes dying.
Check the grounds too!

 

Have the charging ssytem analyzed. If you put a voltmeter on the battery terminals, rev the engine to 1500 rpm and see if the voltmeter shows about 14.4 volts... if it is less, the alternator is not up to snuff. Then get the battery load tested by putting a 1000 amp (it's a big battery) load testing meter on the terminals, putting a load on it and reading the results. If this is good, start looking at wires and connection in the main primary wiring circuit. Then start going through the grounds. It is also a good idea to remove the positive lead from the battery and inserting an ammeter between the battery and the removed cable. If it shows much more than 50 mA, there is a parasitic drain that you need to track down by removing fuses one by pone until the meter drops.

 

Glen,
seen the same thing. I always try to get the parts to fix mine or take my stuff to be repaired instead of giving them mine for a core. the starters are even worse!
I have to laugh when I hear Tom & Ray speak of rebuilt stuff as being just freshly spray painted. One car went through 5 starters because of this. like you said though reman is a different story.

 

Do the 1500 RPM hold and then start turning on accessories one by one. (Lights, fans, etc.) The voltage shouldn't drop more than 1/2 volt. This tests your altenator output.

 

Thanks for your input, guys! I`ll go to service soon and tell them to follow advice I see here. If there are any other tests that may be carried out to find the problem, please let me know.

 

Results???

 

Hi tomfurie

Post is 2 years old. Many OPS never come back with the result, unfortunately. I have been guilty of this myself, and had to be reminded, (on another forum)

 

Hi everyone, has anyone had an electrical issue with their 2006 Jaquar XJ8? If so what was cost to fix. Thanks

 

Ignore. This is an old thread.

 

So many things wrong with that resurrection post!!!! 9-year-old thread, and the most vague question I've ever seen, anywhere! Ever! "How much does it cost to fix an electrical issue?"

My answer: $357,235.19, most of which is Internet improper usage fines!