I have an XJ8, 1998. I've done about 130,000 miles in it. Its great and I love it. Some strange fault developed where the battery drained even though it was running. First symptoms were the central locking becoming intermittent. The alternator works fine and I replaced the battery. Sadly it now won't start as the factory immobiliser has activated through the battery voltage dropping and I can't start the engine. Got the car recovered to my drive but can't start it. Anyone know how I can get past the factory immobiliser? So far the local dealer has failed to find the fault after £350 of labour so not keen to send it there again.

 

Hi Keith, what does the car do exactly when you try to start it? Any clicks under the bonnet?
Have you tried a hard reset, this is holding the neg cable to the pos post on the battery for 20 seconds, clears the memory and it's back to factory settings. Did you have to put the radio code in after you changed the battery?
Also, check the heavy cable connections, passenger side fuse boxes under the bonnet. They have a habit of corroding and really should be unbolted, wirebrushed and reinstalled as a matter of course. Check the earth straps are connected, one on the very front of the bonnet, the other end near a horn, again passenger side. The engine earth is on the drivers side, as the trans tunnel meets the engine bay underneath the car.

Lastly, just a thought.....
If the dealer didn't find the drain, or the no start fault, who's to say the new battery isn't now drained also? Best to put it on charge before you perform the hard reset.......

 

I have a question about a hard reset. Do you leave the positive cable connected to the post while holding the negative cable to the positive post?

 

Yes, you can leave it connected. If it makes you feel better you can remove it from the battery but as far as the battery is concerned, it doesn't care. As long as nothing is connected to the negative post of the battery, no current will flow.

 

Sean,

Thanks so much for coming back to me. I've been away for a few days with no access. To answer your points, when I try and start it I get nothing, no clicks or anything. I haven't tried the hard reset you suggest before - never heard of it. Will give all your suggestions a try this weekend and let you know the outcome.

The battery has certainly been drained previously whilst we have been trying to find this fault and we have had to reset the radio. This is the first time a drain of energy has made the immobiliser come on. It has kicked in and stayed in. Your comments on the possibility of a poor earth certainly ring true; it seemed that it must be something similar but I had no idea where to start. You have given me some good ideas and I am very grateful. I only get time to try stuff at weekends so will certainly go all round your points and check the lot. Many thanks.

 

Hello, I currently replaced the bpm in my 03 super v8 , and I'm having the exact same issue and my car is currently stuck in a friends driveway. I was thinking that maybe my only key has lost code with the car, so was thinking of calling a locksmith and having 2 new keys made along with key fobs. Does anyone think this could be the issue and that new key reprogramming would solve it?? Thanks for any replies in advance!!

 

Hello, I've had a problem with my 2000 XJ8 VDP where it acts like the battery is disconnected and the little red security light on the shifter panel is flashing and that is the only indication that there is power from the battery. No lights, door locks, anything at all. Occasionally after a bit of time it will return the power to the car and it will start. I found that if I disconnect the battery for a few seconds, the problem clears. (Of course you will need the key to open the trunk; the car acts as if it has not power) Also, when it happens it seems like the negative cable is warm. The car can be cold or just turned off like at the gas station.
I ended up buying one of those batter disconnect switches that connects between the negative battery terminal and the negative cable. Now when it happens I unscrew the thing a few turns; then re-tighten and the car power is back.
The link below shows one of these devices. I'm sure there's other places to buy one.
I would like to find out what is causing the problem. I've tried replacing the security module and the key transponder. At this point I don't let my wife drive the car as I don't want it to act up. Also, it might not happen for six months or so. It happened this evening when I was fooling with the car as it's not putting out hot air. It happened a few weeks ago too.

https://www.zoro.com/battery-doctor-...E&gclsrc=aw.ds

 

hello friend , it seems like your issue is most likley a bad ground cable , ive read about this in another thread recently , and the clue to say it might be the negative battery cable is because it geta hot , im sure others will be around with more suggestuons , but i would start here

 

I do have another cable though the one on the car looks to be in perfect condition. No corrosion anywhere. I have been thinking of trying to change it but whats weird, you'd think if it was a bad connection that the car would re-power it self if I jiggled the cable.

 

I only have one key at this point as I somehow lost one some time ago. I'm wondering if there's something about the key. Then again, it goes into this condition when there is no key in the lock. Wiggling the key or shifter or fooling with anything that might be disabling the car does nothing.

 

As suggested by "97xj6lucy", it appears that there is high resistance in the connections of the ground cable (otherwise it would not be getting warm). Unbolt it from the body and clean well the cable lug and the point on the body. Sometimes these cables get corrosion inside their crimps (to the lug and/or to the battery clamp) so try with the other cable you have. Also, open the master fuse box (in the trunk), unbolt the cables and the fuses and clean all connecting surfaces well.

 

Thanks a bunch! I'll do that this weekend.....