In reply to a message from Jaguarpete sent Wed 3 Jun 2015:
Pete…
Thanks for the nod. But while I was working with you I was picking
Bryan’s brain on the subject (I mean really, if you get down to a
solution on ANYTHING with this car Bryan’s probably had something
to do with it … and he no longer even owns a Jaguar !!)
A couple of interesting tidbits that came up on the BFM system:
There are actually two separate monitoring systems that can send a
fail signal to the BFM. The ‘‘Turn/Hazard’’ monitor which only looks
at the turn signal bulbs front and back. This is the one that
needs a ground signal to the VCM. I can only imagine this is a
separate system because of the hazard flashers (which are in fact
the turn signal lights)…perhaps a safety issue.
The other system is the ‘‘general’’ monitor that looks at all the
other external lights. This is the one that requires the 12v
signal. If any of the four BFM’s senses a discontinuity (bad bulb)
in either system it will trigger a bulb failure (the wonderful
digital light bulb with an ‘‘X’’ over it in the VCM.) that everyone
is undoubtedly familiar with.
So even if you don’t ‘‘hack’’ the system this should help you narrow
down your problem:
If you have a bulb warning try your turn signals. If the audible
turn signal sound and the turn arrow on the dash goes to double
speed you have a problem with one of the turn signal bulbs, either
front or back on that side. All the other external turn signal
bulbs on that side will flash normally by the way, except of course
the one that�s failed and sending the signal.
Like wise if both turn signals are normal you have a problem with
one of the other �general� bulbs. I don�t know of a way to tell
which side.
Now that�s the way the system is suppose to work. Warning light
comes on, replace the culprit bulb and all is well. But as many of
you know the four modules (and most particularly the two rear) are
plagued with failed solder joints that give false momentary
warnings. So good luck with tracking that down and either
replacing or resoldering them.
Now I�ve had my Jag for over two decades and have had problems on
and off with false warnings almost the entire time. I�ve tried
resoldering the modules, replacing them with used units and even
prayer�.but nothing keeps them permanently fixed !!
This job took me several hours last weekend and it was worth every
second�…A world without false bulb warnings��.YES !!–
Groove, 1989 XJ6 3.6L
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