[xj40] Is it possible to trick the Bulb failure unit?

XJ40
21

In reply to a message from Nigel Snowden sent Wed 15 Oct 2014:

OK but the problem is human nature means that it probably
will be a long-term ‘solution’!–
The original message included these comments:

Very good points however we were I think all trying to
assist in order that the vehicle could at least get through
the test - don’t think anyone actually advised that the

–
Alan (XJ40 3.6L 1987/8)
Salamander Bay, nr Newcastle, Australia
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22

In reply to a message from Alan4d sent Thu 16 Oct 2014:

My fellow Jaguarist…

All excellent points as far as the plus and minuses of finding a
work around of the infamous bulb failure module.

But as far as I’m concerned I’d dance with the devil to be
permanently rid of that &%!* system.–
Groove, 1989 XJ6 3.6L
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23

In reply to a message from Grooveman sent Thu 16 Oct 2014:

It isn’t rocket science if you are handy with the soldering
iron. The particularly vulnerable points are those with a
large mass, like connectors for the daughter boards. After
removing from the car and opening, carefully inspect each
soldered joint with a jewellers loupe. You will eventually
find one or more than one with a hairline crack round the
base. The purest way of dealing with this is to solder wick
off the old solder completely and put fresh solder on. A
cheap and cheerful way is to heat and reflow the existing
joint. Either way, you need a good hot iron, At least
80watt so that you don’t have to hold it there for an age.
I would offer a service to do these if there was enough
demand. It would help finance a stereo microscope to make
the job (and other electronics jobs) easier! But I’m in
Aus so I guess the need is less.–
Alan (XJ40 3.6L 1987/8)
Salamander Bay, nr Newcastle, Australia
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24

In reply to a message from Alan4d sent Wed 15 Oct 2014:

I’d venture to say that you actually do meet a whole bunch of
cars '‘going the other way’ without BFMs. I know I have.–
The original message included these comments:

I was going to chime in and say that in my opinion trying
to cheat the bulb failure warning system is a highly
dangerous and ill-advised procedure and I am surprised that
so many enthusiasts even talk of it! I just hope I don’t
meet any of them on the highway coming the other way.
I suffered for months from this and the solution was to
find the fault. First of course is the unit doing its
job? ie are there failed bulbs. Second, the most likely
fault in the BFM module itself is a dry soldered joint.
Going through them all carefully using a jeweller’s loupe
will eventually find the culprit, which is what I did. Now

–
Ed Stillwell 1994 XJ6 VDP, Heritage matters
Wayne, OK, United States
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25

In reply to a message from Alan4d sent Thu 16 Oct 2014:

Alan…
(As much as I hate the saying) …’‘Been there, done that’’ !

I removed both rear BFM’s and took them to an electronics repair
shop. They worked well for about a year.

I’ve taken them out twice since then and tried it myself with mixed
results. They initally worked and then little by little the
warning light on the VCM would come on when I went over a bump or
the temperature changed a few degrees.

Totally aggravating!!!–
Groove, 1989 XJ6 3.6L
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26

In reply to a message from Grooveman sent Fri 17 Oct 2014:

I also was plagued by intermittent bulb failures, so I
finally soldered the two torpedo bulbs into the fixtures for
the license plate lamps. That seems to have cured 90% of
the failures.–
The original message included these comments:

(As much as I hate the saying) …‘‘Been there, done that’’ !
I removed both rear BFM’s and took them to an electronics repair
shop. They worked well for about a year.
I’ve taken them out twice since then and tried it myself with mixed
results. They initally worked and then little by little the
warning light on the VCM would come on when I went over a bump or
the temperature changed a few degrees.
Totally aggravating!!!

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
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27

Hi. I know this is an old post but the issue still current for many

I have an 1988 XJ6 that suffers the annoying alarm. Ive spent hours and hours doing everything to get tot he bottom of it - and to no avail. Rather frustrating. Before cutting i seemed to get the alarm to go away with the lights off. But now its back all the time

I ended up cutting the pink and slate to each of the 4 units and i still have the alarm. Any ideas? One of the work arounds talks about soldering the pink slate to the white/pink for a 12 volt ignition feed. But Im assuming Nigel you just cut them and did not add a feed i assume?

I also noticed a pink only cable in my rear units - but i cant find such a cable on the wiring diagrams - only a black/pink which i dont have. I actually cut the pink cable initially and it helped to get rid of the alarm with the lights off initially. But its back now.

I am wondering if its the indicator alarm with bulbs off that can cause this.

I dont want to take out the cluster - everything works on it and i am afraid to disturb it. Can you get to the cables from below without removing the cluster?

The alarm for the indicators is intermittent - fast click

Any help appreciated

28

ok - i decided to have one last go today. Seems my 88 car has pink only wires to the back for the common failure and pink/slate from the front. They come together at the connector under the dash. Easy access to them and didnt need to remove the cluster thankfully. For now i cut both the pink and pink/slate cable that go into one terminal pin in the plug. I then fed one of these cables a 12v ignition feed from the adjacent pink/white cable. Bulb alarm gone.

I left the indicators as were - no alarms most of the time and im hoping with all the cleaning, soldering and bulb replacements this system can stay and will work.

I couldnt see any dry joints inside the units. Im pretty handy with soldering and yet i found its so easy to create a short - with one marker light staying on all the time and losing the dip when going to main at one point. so be careful.

29

n reply to a message from Jaguarpete sent Wed 3 Jun 2015:

http://www.jag-lovers.org/snaps/snap_view.php3?id=1433286916

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

1 Like
30

Ian,

Where are you? Good idea to include your location in the heading so we can know the likely country specification of your Jag.
For example, if you are based in UK/Europe then your car probably has indicator side repeater lamps in the front wings and they can be a frequent BFM warning nuisance.
Since you say you have a ‘fast click’ when indicators selected you may find this thread of interest.

31

Hi Bryan,
I am in the USA with US spec so no side indicators. I have cleaned everything and at the moment it seems the indicators seem ok - we will see.
Real shame to not be able to keep the bulb alarms installed but i really tried everything. So nice not to have the alarm all the time though
r
ian

32

There are two indicator bulbs in each rear lamp assembly, make sure both are good!

33

Thanks Larry - i did thank you. They are good. At the moment no alarm but it comes on after several clicks often when driving. Not driven it since i did the last round of contact cleaning - undoing and cleaning all earth points and cleaning all bulbs. fingers crossed

34

Bad socket, intermittently making and breaking. Clean out the front sockets.

35

thanks. Ive done that - will take another look

36

Ian …

I think in the end you’ll find that the false warnings are coming from a microscopic(s) crack in one of the solder joints in either the left or right rear bulb failure module. My theory is that the small amount of current passing through the joint produces enough heat to temporarily open it up, that’s why it’s intermittent.

Why the rear modules ? In all the years I’ve tracked this problem on the forum and on line I can’t ever remember a problem with the front modules.

My advice is take the time, remove the instrument cluster and hack the system. If not, this problem will come back to haunt you over and over !

37

After a drive today it was back for the indicators. I think the hack is coming. I left the knee panel off so still got easy access to kill it and give it the permanent earth
Thank you for your reply

38

Ian … it takes more than just a ground to do the job. Did you look at this …

http://www.jag-lovers.org/snaps/snap_view.php3?id=1433286916

39

I seem to remember Bryan N having an intermittent Bulb Fail warning that was a broken bulb filament that would vibrate and fuse together then break again?

40

yes saw that - its my reference. But i didnt remove the cluster. You can access the cables from below. I found the pink/slate and pink white and did that fix last night. Just need to disconnect the yellow and take the tail to earth to deactivate the indicator warnings. Ill give the bulbs another check first