I heard a funny sound while trying to lock the car with the remote key fob
the other day. “Batteries must be giving out” I thought. I used the key to
lock the car. I dutifully replaced the batteries within the required 2
minutes with the proper size (2 size CR2016 lithium 3v batteries from Radio
Shack for $10.45). Armed with reprogramming instructions from the Jag book
just in case, I tried out the newly re-energized remote. The car promptly
unlocked but the same strange sound came from the front as I tried to lock
it.
Duh!!! The trunk had been unlocked and the security system was trying to
tell me (even with the old batteries) that it could not lock the car
remotely unless I attended to the open trunk. Let that be a lesson to me …
and to anyone else as slow as I am.
At least I have new batteries in my one surviving remote key fob. Another
day. Another Jag lesson.
Eliot Brenner
Annandale, Va.
'97 x300L with 121.7k on it
In reply to a message from eliot brenner sent Sun 12 Dec 2010:
We all do stuff like this Eliot, difference comes in whether we are
wise enough to admit it. Life’s lessons are never wasted on those
with an open mind.
It just happens that I spotted your fob topic with something fresh
in my mind that I’ve been meaning to discuss for some time;
Constant reference is made to replacing fob batteries within a very
short time, seconds perhaps, a couple of minutes etc., presumably
on the basis that the fob will somehow lose its memory and no
longer work.
There are 2 reasons why I don’t think this is true, one is merely
reasoning and the other is proven practically.
Reason shows that the fob transmitter has a unique code which can
never be lost, it is imprinted on some chip or other in the fob
(ROM), and will remain whether the batteries are good or not. After
all, to assign or register a fob to the car’s security system
requires us to teach the CAR to recognise that unique fob code, not
to give the fob a code. Thus, the car will not forget the fob code
just because the fob batteries went flat.
Secondly, I have fitted new batteries to apparently dead fobs where
the car has been unused for months (as I did today) or years in
some cases. If the fob is viable in all other ways (not damaged nor
internally dirty) then it will work just as it did before when some
fresh batteries are fitted. The fob does not need re-registering to
the car and doesn’t know it shouldn’t work…!
For these reasons I think the claim that fob batteries must be
replaced in a furious panic is no more than a hoax, a bit of a wind
up perpetrated by some mischievious person and then passed on by
others because they think it must be true. I don’t think it is.
In reply to a message from Jags on gas sent Tue 14 Dec 2010:
Steve,
I’ll go with that, I’ve tried to de-programme a fob and
leaving the batteries out for a long period and/or shorting
out the +/- and using the buttons does not stop it working!–
The original message included these comments:
For these reasons I think the claim that fob batteries must be
replaced in a furious panic is no more than a hoax, a bit of a wind
up perpetrated by some mischievious person and then passed on by
others because they think it must be true. I don’t think it is.
In reply to a message from Neil Maldon sent Thu 16 Dec 2010:
My real point is that one cannot prgram nor de-program a fob. If it
has good batteries it will work, if they go flat, it will not. The
fob is simply a dumb transmitter of a pre-set code. This can be
proven by taking a fob from one car and registering it to another
car, whereupon it will be recognised by both cars. The fob hasn’t
changed its code at all.
So, when we register a fob to a car, it is the car we teach to
recognise the fob’s code, we teach the fob nothing and nothing can
be lost in the time it takes to change batteries over a coffee, nor
a week.
In reply to a message from Jags on gas sent Thu 16 Dec 2010:
Steve,
It’s intriguing to know how the code is set in the ROM, i.e.
is it randomly generated at 1st. power up or set during
manufacture and also whether each chip is unique or are
there multiples out there?
I started with one fob that came with the car and have
acquired two more used ones that have now been programmed to
the car or vice versa, it would be interesting to know
whether the code is set by the fob manufacturer or the
Jaguar Main Dealers or both.
Your logic is unquestionable.–
The original message included these comments:
My real point is that one cannot prgram nor de-program a fob. If it
has good batteries it will work, if they go flat, it will not. The
fob is simply a dumb transmitter of a pre-set code. This can be
In reply to a message from Neil Maldon sent Fri 17 Dec 2010:
Neil,
I don’t know, but I ‘think’ that the code is placed during
manufacture, randomly, just as it must be in the chip of an
ignition key. This is a good analogy, as ordering a blank key
requires at least the last 6 of the VIN to ensure that the chip
will be coded in the correct range for the model year etc., and
when that key is cut to mechanically fit the lock we have to teach
the car (not the key chip) to recognise and store that chip code.
This analogy makes the workings of a fob transmitter even clearer,
as the key/chip has no battery at all, it must be coded when it is
made. Following this logic, all the batteries in a fob do is to
make the transmitter work, report the embedded code, they have
nothing to do with code storage per se.
Clearly if a random selection of codes is used during manufacture
for both key chips and fobs, there is a reasonable chance of
duplication.
Regards
Steve–
The original message included these comments:
It’s intriguing to know how the code is set in the ROM, i.e.
is it randomly generated at 1st. power up or set during
manufacture and also whether each chip is unique or are
there multiples out there?