[xj40] Could these be related?

94 inline 6, 169 k miles.

  1. the tail lights (parking) aren’t working. All others,
    stop, reverse, turn signal all fronts are working. I got the
    DBC10009 replaced but still not working. It would be that
    the ‘new’ 10009 was also bad when they sent it to me.
  2. I keep getting the Fuel Failure 37. I unhooked the blue
    solonoid thing, it looks really clean, the hose also look
    clean. I put contact grease and it keeps coming up again
    (reset it several times with battery disconnected).
  3. when I use the door lock button it used to just lock and
    unlock, but now when I try to unlock the doors, it will
    actually raise all the windows and close them.
  4. just bought new battery a few days ago. but when I start
    the car, the dash dial (above the fuel guage on the left)
    reads around 10 Vs. (no problem starting), then as I pick up
    the speed it will go past 13 and closer to 15 on the meter.
    I think around 30 mph. so basically the volt thing
    fluctuates. now it would be just a bad alternator.

any thoughts would help.

thanks again–
94 XJ40 (xj6)
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In reply to a message from newcat2007 sent Mon 25 Jun 2012:

  1. That same part of the DBC10009 Relay Module ‘H’ which
    controls the tail lights also controls the front side lights
    (parking lights) on both sides of the car, so if the latter
    are working, the tail light problem is nothing to do with
    the DBC10009.
  2. FF37 is often triggered by low battery voltage when you
    first switch on the ignition. Of course, once flagged it
    will remain on until you clear the computer memory by
    removing the negative battery cable for a short time or by
    pulling the instrument pack fuse while the ignition is on
    but the engine not running as described previously on this
    forum.
    3)Do you mean the ‘panic button’ on the dash? On my '91 that
    closes the widows (and sunroof)if open when the button is
    held down after initially locking the doors - it does not
    have an ‘all unlock’ function. As I say, that’s how it works
    on my '91 but IIRC, didn’t they change that on the '94 so
    that the ‘panic’ switch also unlocks all of the doors when
    pressed a second time? Perhaps holding it down still closes
    any open windows???
  3. I suggest you use a voltmeter directly on to the battery
    to check it out. Here’s a post I did a while back to show
    how mine performs :-

http://forums.jag-lovers.org/avsn.php?1534448n29

How does yours compare?

Of course, while cranking the engine, the battery volts may
drop to 10 volts until the engine fires.

Have you checked the battery voltage in the engine bay at
the firewall terminals? I believe corrosion there is often
the cause of battery / charging problems on
‘battery-in-the-trunk’ '93 / '94 cars.–
The original message included these comments:

  1. the tail lights (parking) aren’t working. All others,
  2. I keep getting the Fuel Failure 37. I unhooked the blue
  3. when I use the door lock button it used to just lock and
    unlock, but now when I try to unlock the doors, it will
    actually raise all the windows and close them.
  4. just bought new battery a few days ago. but when I start
    the car, the dash dial (above the fuel guage on the left)
    reads around 10 Vs. (no problem starting), then as I pick up


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Mon 25 Jun 2012:

Umm. so all the parking lights (front and back) work off the
same circuit huh? I wonder what could be wrong then. could it
be some sort of bulb failure thing on the back? some sort of
bad circuit on the plate that the actual light bulbs sit on?–
94 XJ40 (xj6)
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In reply to a message from newcat2007 sent Mon 25 Jun 2012:

It is not true to say ‘‘all the parking lights (front and
back) work off the same circuit’’. In fact exactly the
opposite is the case - each front sidelight or rear tail
light is separately fused and grounded through their
respective BFM.

Relay Module ‘H’ (DBC10009) is common to all four lights
only in respect that it energises the individual light’s
relay in their respective BFM when the light switch is
turned on. In the case of the rears, DBC10009 also energises
the respective relays for the license plate and rear side
marker lights, both also being fed battery power from the
same fuse as their respective tail light.

Are the license plate and side marker lights illuminating on
your car?

Have you checked the tail light bulbs. Bit of a coincidence
if bulbs for both tail lights have blown, but one never
knows on a Jag! :-)–
The original message included these comments:

Umm. so all the parking lights (front and back) work off the
same circuit huh? I wonder what could be wrong then. could it
be some sort of bulb failure thing on the back? some sort of
bad circuit on the plate that the actual light bulbs sit on?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Tue 26 Jun 2012:

they have new bulbs (the back tail light). all other lights
work, the license plate, the reverse, stop and turn. just
both rear parking lights dont’ work. so i’m at a loss. don’t
know what to do. it would seem very unusual for JUST the
parking lights on the back to not work, with all others
working.

the voltage on the battery read 12.6V overnight. it starts
fine but the dash volt meter still reads less than 13 with
the car running. also put the volt meter on the battery
while it was running and I get about 12.6. now that being
said, when I drive around for awhile and I get a belt squeel
and then the volt thing goes up to around 14. so maybe the
alternator is going bad on me?–
The original message included these comments:

It is not true to say ''all the parking lights (front and
Are the license plate and side marker lights illuminating on
Have you checked the tail light bulbs. Bit of a coincidence


94 XJ40 (xj6)
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In reply to a message from Bryan N sent Tue 26 Jun 2012:

Also, as stated before I put a new battery, but it seems
that the battery keeps getting drained. when I start up in
the am, it needs a jump. works fine when I drive it around,
when the engine is on the battery volt shows around 13.4.

so, I don’t think its the alternator. that being said, could
there be something that’s draining the battery? This is a
new problem (btw, the car has been sitting around for close
to 2 years without being driven), as it was not there
before. it has new plugs, caps, rotors, oil, filter. How
should I go about trouble shooting? nothing obvious is ‘on’
that could be draining to my untrained eyes/ears.

thanks–
94 XJ40 (xj6)
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In reply to a message from newcat2007 sent Tue 26 Jun 2012:

The normal procedure to detect battery drain is to measure
the ‘dark current’ - i.e. the current drawn from the battery
when the engine has been shut down and everything has been
shut off, no alarm set and with doors and boot closed.

I do that by disconnecting the negative battery lead and
connecting an ammeter in series between the battery negative
lead and the negative battery post. On a '93 / '94 it a
little more awkward with the battery in the boot because you
need to position the ammeter so that you can adjust the
range and read it from inside the car with the doors closed.

Before closing the doors, you also need to remove the fuse
box covers from the ‘A’ post fuse boxes because you are
going to pull and replace each fuse in turn in both boxes to
witness any significant reduction in current readings on the
ammeter.

Ordinarily the dark current draw should settle down to about
40 milliamp a few minutes after everything is shut down. If
it is significantly higher than that, you keep
pulling/replacing each fuse until you find the circuit(s)
which is(are) causing the excessive current drain and then
trouble-shoot that circuit from there.–
The original message included these comments:

Also, as stated before I put a new battery, but it seems
that the battery keeps getting drained. when I start up in
the am, it needs a jump. works fine when I drive it around,
when the engine is on the battery volt shows around 13.4.
so, I don’t think its the alternator. that being said, could
there be something that’s draining the battery? This is a


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from newcat2007 sent Tue 26 Jun 2012:

I agree it is unusual.

Let’s analyse what is not wrong on either side from the
information you have so far provided.

  1. You say that the bulbs are good on both sides
  2. If the license plate lights work, then battery power is
    going in to the BFM relays for both the license plate lights
    and for the tail lights (same fuse)
  3. If the reversing lights work, then the tail lights
    grounds are good because they share the same ground points
    (although the reversing lights are on a different fuse)
  4. If the license plate lights work then the signal from
    DBC10009 is reaching the respective relays in the left and
    right rear BFMs because they are energised by that signal on
    the same wires as the relays for the tail lights.
  5. Finally, the front sidelights work as well as the other
    lights mentioned so the light switch is demonstrably OK.

SO, as far as I can determine from what you have reported,
the only factor which will prevent both the tail lights
from illuminating is if both tail light relays in their
respective BFMs have failed. We know that those relays are
being fed with battery power from their respective fuses and
the switching signal from DBC10009 to energise those relays
is getting through but power is not getting through to the
bulbs because if it were, since the grounds are good, good
bulbs must illuminate.

Perhaps someone else can come up with a simpler theory on
why your tail lights are not working! :-)–
The original message included these comments:

they have new bulbs (the back tail light). all other lights
work, the license plate, the reverse, stop and turn. just
both rear parking lights dont’ work. so i’m at a loss. don’t
know what to do. it would seem very unusual for JUST the
parking lights on the back to not work, with all others
working.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Tue 26 Jun 2012:

Thanks for the long logic.

A few more things I should add. I actually notice that the
left side marker (on the back left, small little bulb)
doesn’t work. The right side marker works. I changed the
bulbs and only the right side works. Also, I noticed that
the left back license plate light does NOT work. I didn’t
take notice before cause I thought there was just one. The
right license plate light works.

So far this is what is not working:

  1. both parking lights
  2. the left license plate and side markers don’t work.

The reverse, brake, turn signals all work both front and
back.–
The original message included these comments:

I agree it is unusual.
Let’s analyse what is not wrong on either side from the
information you have so far provided.


94 XJ40 (xj6)
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In reply to a message from newcat2007 sent Tue 26 Jun 2012:

OK, if, on the left side, neither the tail light, the
license plate light nor the side marker illuminate (and
assuming that all of their respective bulbs are good and
making proper contact in their holders) the problem could be :-
a) Fuse #C7 in the left side fuse box is blown OR there is a
bad solder joint at the back of that fuse socket**
preventing battery voltage (‘always hot’) getting to the
left rear BFM on the Brown/light green wire at pin 1 of its
18-way White connector - OR
b) The switching signal from Relay Module ‘H’ (DBC10009 -
‘hot’ only when the sidelight switch is turned ON) necessary
to energise the three individual relays for those three
lights in the left rear BFM is not getting through to the
BFM on the Red wire to pin #18 of that 18-way White connector.

[** Note :- On '94 MY cars (VIN 687219-on) for reasons (not
being an electrician!) I do not fully understand, they
introduced a diode in that Brown/light green wire from fuse
C7 in the left side fuse box feed to the left rear BFM.
(They do not have a similar diode in the feed from the right
fuse box to the right rear BFM). That diode, marked ‘LSD4’,
is spliced in to that Brown/light green wire under the left
side sill carpet some 36 inches from the left side fuse box
(presumably as it runs back towards the left rear BFM). I
guess if that diode goes open circuit you get no power to
the left rear BFM for the three lights you are missing]

You need to check in a) and b) above that you have battery
voltage at pin 1 (always hot) and pin 18 (hot when light
switch is ON) of that 18-way White connector on the harness
at the left rear BFM.

As mentioned before (although you should still check for
continuity to ground from the bulb socket just in case) the
appropriate grounds for those three lights should be good.
The left tail light is on the same ground wire as the left
reversing light and the latter works OK. The left side
marker goes to the same ground point in the trunk (floor
below left rear BFM) as those two (and the turn / stop
lights) so that should be good and the left license plate
light has a common ground with the right license plate light
on the right side of the trunk under the right rear BFM.

Good hunting! :-)–
The original message included these comments:

So far this is what is not working:

  1. both parking lights
  2. the left license plate and side markers don’t work.
    The reverse, brake, turn signals all work both front and
    back.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Wed 27 Jun 2012:

thanks alot of info.

i think its gonna probably end up being a BFM, in which case
i should just replace the BFM on both sides, which should
cost $500? I wonder if I can switch the BFM from the right
side to the left side. remember the right side license plate
and side markers are working.

my other option is to not drive during night time and if I
do, use my fog lights on the back which work.–
The original message included these comments:

OK, if, on the left side, neither the tail light, the
license plate light nor the side marker illuminate (and
reversing light and the latter works OK. The left side
lights) so that should be good and the left license plate
Good hunting! :slight_smile:


94 XJ40 (xj6)
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In reply to a message from newcat2007 sent Wed 27 Jun 2012:

Yes you can swap the BFMs left and right at the rear to see
if the left side’s faults travel over to the right side.

But before buying replacement BFMs I would open them uo,
find which relay is responsible for each failed light and
see if it works when the relay points are operated manually.
Might be a cleanliness or a soldering problem.–
The original message included these comments:

I think its gonna probably end up being a BFM, in which case
I should just replace the BFM on both sides, which should
cost $500? I wonder if I can switch the BFM from the right
side to the left side. remember the right side license plate
and side markers are working.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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