Our '05 Jaguar XJ8 had been parked for nearly four months with a quality battery tender attached. It had always ran fine and I replaced the original battery one year ago. Last week, when I tried to start it, nothing happened at all except all the lights went dark as I turned the key. I tried a jump box, nothing. I tried to jump it and even did that with a jump box, nothing. I replaced the battery with a new one and nothing. I did notice that the headlights were very dim from not getting enough power. My mechanic says it is probably a bad ground somewhere. He suggested I try to jump it from inside the engine bay, that there should be a hot post somewhere and a body ground. It is all shielded in there, I don't know where to start. Does anybody have an idea what has happened?

 

Might as well find the fault - with the lights dim it's an easy job to go round looking for the voltage drop.

 

Faulty battery.

That connector is what they use at the factory when the car is being transported around. Out of the factory it has no official use. Though I am sure you can find a use for a switched power source in the boot/trunk?

 

hey, I have changed the battery since and still the same issue. Looks like the car has good power as the windows etc c are working correctly. Do you have any faut codes on the dash???
Im waiting to change all the relays in the car and also the climate control is still not getting power for some reason when it was right before the car cut out.

 

Everything looks normal on the dash until I turn to start, then all goes black until I release the ignition. It does have a restricted performance message. There must be some sort of heavy battery drain, the headlights are dim. My Foxwell obd scanner says ECM fault I4 or 14.

 

Well ur in a better position than I am, at least ur obd is working. So yes u must have a ground issue I presume.

 

Had it towed to the Dealer. They discovered my fear because the car sits outside. Animals had eaten wires causing all kinds of shorts. They repaired the wiring then I picked it up and went home, ran great. The next day I drove to work, everything was fine. When I drove home the check engine came on upon start. I panicked, thinking some how the animal found it's moved home and was busy all night. My OBDII scanner said it was a bad O2 sensor. I did not want to mess with it, though I should have. I took it back to the Dealer and that was the malfunction. It runs great again now and this time I will make sure to often enjoy driving it. We only have a one car garage and four cars. My 2001 Honda S2000 #82, never been rained on, with less than 10,000 miles gets that spot. Our Jag has 43,000 miles.

 

This type of thing happened to my S T R and in this instance you have identified the fault however for future reference the part which failed on my car was the rear ABS sensor on the near side (UK).
I was astounded to see what this little fella could throw up in the fault code arena.
Everything was screwed. Gearbox overheat, ABS, Cruise not operative, no communication error, failure to start, and loads more.

The abs is sensed before the wheels turn to ensure they re all stationary, then at about 15mph, then at higher speeds and continuously through the journey.

Leaning the sensor can fix it as the get dirty and the dirt is magnetic but the best option is to replace the sensor.

Disconnect the battery before pulling ANY plug on a Jag or.