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Discussion Starter #1
Hoping to avoid a trip to dealership with the collective knowledge here, thanks in advance.
Replaced car battery and since then I can't start the car unless I hold the key fob up to the dash in the spot where the dock was in older models. Once I get it started I have no issues, but the fob also can not be used to unlock or lock. Tried both fobs, and new batteries in both, same issue, have to hold up to dash to get it started, any thoughts?
 

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Take it apart, take out the battery and squeeze the terminal down before replacing the battery and reassembling. Happened to me and this cured it.
But the fobs are sensitive to cheapo batteries so make sure you've got a quality battery in there, such as Duracell for example.

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MY 2012 XF S Portfolio Ultimate Black
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I only can add that if you have used a cheap or old lithium battery this could happen. Use Energizer or Duracell and make sure it is genuine. It won’t work with cheap ones.
 

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And don't buy them online or from a cheap $1 store, there's many brands being faked now.
 

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Discussion Starter #5
I tried all the above suggestions, went and bought a Duracell and it had no effect.
 

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Do you get any messages in the dash?
 

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When you changed the battery did you wait at least 10 mins or waited for the boot light to go out with the boot open before disconnecting the battery.
 

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Discussion Starter #9
When you changed the battery did you wait at least 10 mins or waited for the boot light to go out with the boot open before disconnecting the battery.
No I didn't wait when I disconnected it
 

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When you changed the battery did you wait at least 10 mins or waited for the boot light to go out with the boot open before disconnecting the battery.
I recently learned it is 33mins for cars before MY13 and 20mins for cars made after that.
 

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I recently learned it is 33mins for cars before MY13 and 20mins for cars made after that.
There's been a lot of talk about letting the system shut down because of a couple of instances of problems with, I believe, facelift X250s. My experience with my X351 (and previously with a pre-facelift X250) is that it is not required to let the system shutdown. I have swapped batteries and disconnected the battery for electrical work in both cars without issue.
 
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There's been a lot of talk about letting the system shut down because of a couple of instances of problems with, I believe, facelift X250s. My experience with my X351 (and previously with a pre-facelift X250) is that it is not required to let the system shutdown. I have swapped batteries and disconnected the battery for electrical work in both cars without issue.
I think John, it is a bit like shutting down a computer when updating etc. You may get away with it most times, but you may be unlucky with disastrous results. I think it is best to leave it a while just to be on the safe side
 

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Do you get any messages in the dash?
It just says smart key not found
On a facelift XF that usually means your CJB/BCM is suffering from corrupted VIN values, it can be re-flashed by someone like @Onotole from the RJB, it's only a temporary fix though and any further battery disconnect will cause the same fault. A re-programmed to your car second hand CJB/BCM or a new one are the only long term answers.

That is definitely correct for an XF, I have no idea whether it's the same for an XJ.. but, all of your symptoms are exactly the same as mine were with the exception that holding my fob up to the dash made no difference to starting the car.


P.S. Dealers in the U.K. are not capable of the above temporary fix or re-programming of a second hand CJB/BCM, no idea whether it's the same where you are.
 
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On a facelift XF that usually means your CJB/BCM is suffering from corrupted VIN values, it can be re-flashed by someone like @Onotole from the RJB, it's only a temporary fix though and any further battery disconnect will cause the same fault. A re-programmed to your car second hand CJB/BCM or a new one are the only long term answers.

That is definitely correct for an XF, I have no idea whether it's the same for an XJ.. but, all of your symptoms are exactly the same as mine were with the exception that holding my fob up to the dash made no difference to starting the car.


P.S. Dealers in the U.K. are not capable of the above temporary fix or re-programming of a second hand CJB/BCM, no idea whether it's the same where you are.
Gear Dod......I have been as lucky as John McOBC then......changed battery on both fobs and all was immediately operational with no waiting time, but I will wait in future if this can be the result.
As an aside, I was always told not to hold these transponder batteries on the flats, but only by the absolute edges, for fear of shorting them out via one’s own static/earthing. Is this really the case mins.....? Have even taken to wearing nitrile glovey fingers noo......lol....!
 

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Its not the fob batteries that are the problem BigKev, it's the main car battery.. and this is the first time I've heard of it on an XJ, only ever heard of it on the facelift XF before.
 
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I was always told not to hold these transponder batteries on the flats, but only by the absolute edges, for fear of shorting them out via one’s own static/earthing. Is this really the case
It's good practice not to rub your fingers all over small batteries. Not because of static, but because of dirt and moisture on your fingers. Because the insulator beteween + Positive and - Negetive is very small, it would be easy to leave deposits behind from your fingers and thus cause a short which could drain the battery and reduce the battery life. Of course, this is all technically possible, I'm not aware of it happening on a regular basis...if at all. But as I mentioned earlier, it good practice to be carefull when handling these minature batterys.
 
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