[xj40] [XL40] 1991 Soverign Headlight - VCM Problems

I have a 1991 XJ6 Soverign that the passenger low beam and
fog light quit workimg, high beam is fine. VOM measures 2.4
volts at the low beam connector. Fog lamp has a stone crack
in lens. Lighting bolt is on display but when I push the VCM
button it does not display and only resets the trip
computer. All fuses checked and no bad ones found. I pulled
the fog lamp and a VOM measures 17.5 volts in the off
position and 0 volts on. It was working fine, just went out,
any thought?–
XJ6-CA
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In reply to a message from XJ6-CA sent Sun 30 Sep 2007:

Welcome to the forum.

First the VCM. I know this may be a silly question, but are
you sure you are pressing the ‘VCM’ button and not the
‘Reset’ button below it to read a VCM message?

To check if the VCM is working at all, on the first start of
the day, turn on the ignition to position (II), listen for
the Teves pump working and watch the ‘ABS’ and ‘BRAKE’
warning lights. BEFORE either of those lights goes off,
press the VCM button. It should read ‘FAIL’ because the pump
has not yet pressurised the accumulator above the lower
switching limit. As the ‘ABS’ and ‘BRAKE’ lights extinguish,
the FAIL warning should disappear.

Since you have a lightning bolt warning on the dash, my
guess is that you do have a blown / missing fuse or a bad
connection in the fuse holder. The fact that both your right
low beam and fog light have quit suggests to me that the bad
fuse is C7 in the right side fuse box (Circuit 1 on the VCM)
which serves both of those lamps. You need to check those
fuses electrically as well as visually to be sure. Sometimes
the break cannot be easily seen with the naked eye.

You may also wish to check fuse #2 in the centre fuse box.
That provides ignition switched power to the relays in the
right front BFM to power the right front low beam and fog
light. However, that same fuse serves the relays in the left
rear BFM to switch on the left rear fog light and left rear
reversing light. Are those two rear lights working OK?

Let us know what you find.–
The original message included these comments:

I have a 1991 XJ6 Soverign that the passenger low beam and
fog light quit workimg, high beam is fine. VOM measures 2.4
volts at the low beam connector. Fog lamp has a stone crack
in lens. Lighting bolt is on display but when I push the VCM
button it does not display and only resets the trip
computer. All fuses checked and no bad ones found. I pulled
the fog lamp and a VOM measures 17.5 volts in the off
position and 0 volts on. It was working fine, just went out,
any thought?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridge, United Kingdom
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In reply to a message from Bryan N sent Sun 30 Sep 2007:

Thanks for the C7 tip, it was blown, was checking wrong
fuses. The VCM did not pass the ignition on position (II)
test. When pushed it shows 0.0 on the display and resets
the trip computer just like pressing the reset button. The
trip computer and speed control work fine but there is no
illumination of the panel no matter what buttons are pushed,
I have read some models had solder joint problems on the
board, seems VCM is not working and pushing the VCM button
is triggering a reset of the trip computer, any other ideas?–
The original message included these comments:

In reply to a message from XJ6-CA sent Sun 30 Sep 2007:
To check if the VCM is working at all, on the first start of
the day, turn on the ignition to position (II), listen for
the Teves pump working and watch the ‘ABS’ and ‘BRAKE’
warning lights. BEFORE either of those lights goes off,
press the VCM button. It should read ‘FAIL’ because the pump
has not yet pressurised the accumulator above the lower
switching limit. As the ‘ABS’ and ‘BRAKE’ lights extinguish,
the FAIL warning should disappear.


XJ6-CA
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In reply to a message from XJ6-CA sent Sun 30 Sep 2007:

pushing the VCM button is triggering a reset of the trip
computer
IIRC, pressing and holding the VCM does that. Pressing and
releasing it once should bring up the display.–
JagFab,1989MY JaguarSport XJR 3.6 (RHD) + 1998 3.2 XJ8 (RHD)
London, United Kingdom
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In reply to a message from JagFab sent Mon 23 Feb 2009:

LOL…sorry, folks! I have no idea how a post from 2007
appeared at the top of my ‘Recent Posts’ list. I guess I
wasn’t paying attention and used an old bookmark or something…–
JagFab,1989MY JaguarSport XJR 3.6 (RHD) + 1998 3.2 XJ8 (RHD)
London, United Kingdom
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