I have a 2001 XK8 where I disconnected the battery for 2 months and it wouldn't start when I hooked everything back up. It cranked over okay but no start. Had it towed to mechanic who checked it out with no success until he told me to bring in extra key. It started right up. 6 months later same scenario. Car sat for 3 months with battery disconnected and then it would only crank over but no start. I tried both keys and the valet key with no success. Is it likely that the transponders in the three keys would fail?

 

Highly unlikely the transponders are bad. I'm sure it has something to do with the security module after reconnecting your battery...and probably just a timing thing. Instead of 'disconnecting', what about using a battery maintainer for such long periods of non-use?

 

Thanks for the info. Because any programming would have to be done by Jag dealer I had the car towed there. No transponder issue and no security module issue. They said the fuel pump had failed. $1,300. Does this make sense?

 

Failed fuel pump after a lay up makes sense but $1,300 is a bit eye watering.