[xj-s] Cruise Control is Nonoperative

XJ-S
1

Car is a 1995 XJS 2+2:

Here is what I have done so far to troubleshoot:

(1) Checked the #5 cruise control fuse…it is okay.

(2) Also checked the rubber bellows unit on the drivers side
of the engine…it doesn’t appear to be torn and holds vacuum.

(3) Read in the archives that sometimes the ‘‘brake light
switch’’ on the brake pedal can be a source of trouble.
Archives suggested tapping the brake pedal and then seeing
if cruise control would engage. Tried this and it made no
difference. Brake lights are okay.

What is the next step in troubleshooting this issue?

I’ve ordered the service manual on CD, but it won’t get here
for a week or so…so could someone send me any official
Jaguar literature on diagnosing cruise control issues?

I also read that there is a ‘‘cruise module’’ under the
passenger foot well. I pulled that panel down but don’t see
any cruise module (pictured as an aluminum box on E-Bay).
Is it down there?..and if so, where in relation to the fuse
bank?

Lockheed,

I came across an old post of yours that I think deals with
the OEM Jaguar system. Here is what you said:

‘‘You will see there are actually two ‘‘Brake Light’’ switches,
the ‘‘Brake Switch’’ (NC) operates in series with a ‘‘gear
selector switch’’ (NO) which closes when the gear selector is
put in the ‘‘D’’ range. The other switch is the ‘‘Stop Light
Switch’’ (NO). All three of these switches must operate
correctly or your cruise control will not work. If your
brake lights are working correctly, then the ‘‘Stop Light
Switch’’ is OK. You can check the other two switches by
disconnecting the Cruise module plug, turning the ignition
to ON/Run (don’t start the engine!), and put the gear
selector in ‘‘D’’. You should have 12V at the yellow/red wire
of the cruise module plug.’’

‘‘If the above switches check OK, then you might have fault
with the Resume switch or the Master switch, or some of the
components under the hood. Checking the Resume switch is
easy - when you press it, the Blue wire at the cruise module
plug should read about 330 ohms to ground with the Master
switch off. Checking the master switch is a bit more
involved…’’

What do you mean by NO and NC? I’ll try these tests but
first must find the module…

Also, how did you gather this information on how to follow
this diagnostic procedure? From the CD service manuals?

How can I test the master switch?
How can I test to see if the cruise module itself is okay?

Also read about something called a pump that is related to
the cruise…

Thanks for the continued help!–
jstjagguy
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2

In reply to a message from jstjagguy sent Fri 24 May 2013:

''What do you mean by NO and NC? I’ll try these tests but

first must find the module…’’

NO means normally open, and NC means normally closed - and in each
case, means they will remain that way until some action or event
causes them to alter their state. For example, stepping on the
brake pedal will cause the NO switch (Stop Light Switch) to be
closed, and the other (Brake Switch) will go from NC to open; and
when the brake pedal is released they will go back to their
original state. In the cruise control schematic (from
the ‘‘Electrical Guide’’) that you should have downloaded, you will
see these two switches in Fig 21. The chart above - also Fig. 21 -
gives the locations of the components and other information as well.

''Also, how did you gather this information on how to follow

this diagnostic procedure? From the CD service manuals?’’

No, from the electrical schematic logic.

‘‘How can I test the master switch?’’

You may not have to, as it pretty reliable - leave it till last,
and if your cruise begins working before you get there, you won’t
have to. Just in case, unplug the switch from the harness and
using your VOM, make sure the switch positions follow the logic
given by the schematic.

‘‘How can I test to see if the cruise module itself is okay?’’

Forget about it - unless you can find a tester from a Jag Dealer
(who are not interested in keeping our old cars running and don’t
keep the old equipment to test our old stuff). You will probably
have more luck finding a good used one on E-Bay. Again, there have
been few to none that have actually found a bad module - the faults
are usually elsewhere in the system as is the case with the master
switch. However, if you want to actually look at it, and reseat the
plug (or use the plug for circuit testing) to defeat some
corrosion, it is under the carpet just forward of the passenger
seat (under the little tin doghouse) and outboard of the passenger
seat controller module according to the Fig 21 component location
chart.

''Also read about something called a pump that is related to

the cruise…’’

Yes, if you look near bottom center of the Fig. 21 schematic, you
will see an item labeled ‘‘Control Valve’’ - maybe somewhat of a
misnomer, but within that block you will see a small motor - the
pump. This pump supplies the vacuum that is used for the cruise
control bellows. I guess Jaguar finally figured out that when you
go up a steep hill and the engine vacuum drops, the cruise control
can’t hold the speed - sort of like the old vacuum powered
windshield wipers before everybody concluded that electric wipers
work much better when you are going up steep hills. Just took
Jaguar a while to come to the same conclusion with the cruise
control.

In conclusion, don’t forget to test the ‘‘Resume’’ switch at the end
of the turn signal stalk - take a look at the schematic to find a
way to test it. I’ll cover that later if you get stuck.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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3

In reply to a message from lockheed sent Sat 25 May 2013:

Hi Lockheed,

(1) Checked rear brake lights again…all three light up as
designed: the two on the tail lamp cluster and the one on
the trunk lid…

(2) Did the 12 volt test at the red/yellow wire at the
cruise module. Did not have 12 volts…my VOM read 0
volts…I used the car’s floorboard as a ground…

Questions:

(1) I noticed that the bulb outage light comes on with the
brakes applied…even though the three brake lamp bulbs seem
to function as designed. Could this point to the brake
light switch as the source of my problems, even though the
brake lights seem to function as designed?

(2) If not, or to do further diagnostics, how can I test the
other two switches you mention are in series?

(3) It sounds like the most common issue is the brake light
switch. If further testing is not feasible, would this be a
good time to order one and see if it fixes the cruise?

Thanks for your continued help.–
jstjagguy
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4

In reply to a message from jstjagguy sent Sat 25 May 2013:

‘’(1) Checked rear brake lights again…all three light up as

designed: the two on the tail lamp cluster and the one on

the trunk lid…’’

How many bulbs are in the one on the trunk lid - are they all
working??

‘’(2) Did the 12 volt test at the red/yellow wire at the

cruise module. Did not have 12 volts…my VOM read 0

volts…I used the car’s floorboard as a ground…’’

There is no RY (red yellow) wire at the cruise control module. I
assume your looking at the YR (Yellow with Red stripe) wire at
terminal 12 of the cruise module. There will be 12V there only if
the ignition switch is on, the brake pedal is not depressed, and
the gear selector is in Drive - the engine need not be running.

Gotta go eat dinner - back later.

Questions:

(1) I noticed that the bulb outage light comes on with the

brakes applied…even though the three brake lamp bulbs seem

to function as designed. Could this point to the brake

light switch as the source of my problems, even though the

brake lights seem to function as designed?

(2) If not, or to do further diagnostics, how can I test the

other two switches you mention are in series?

(3) It sounds like the most common issue is the brake light

switch. If further testing is not feasible, would this be a

good time to order one and see if it fixes the cruise?–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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5

In reply to a message from lockheed sent Sat 25 May 2013:

Hi Lockheed,

There are four bulbs in the brake lamp bezel on top of the
trunk lid. I took them out to check them…they’re all working.

Also: this time the bulb warning light did not come on when
I depressed the brake pedal…and normally it does not come
on when the brakes are depressed…so I’m not sure this is a
reliable piece of information in the equation here.

When I did the 12 V test at the YR wire I did exactly what
you suggested…power but no ignition…car in drive. Did
not get 12 V, instead it measured 0 V.

Considering that I don’t have 12 V at that YR plug, what
would you recommend I do next?

I owe you a couple of beers…–
jstjagguy
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6

In reply to a message from jstjagguy sent Sat 25 May 2013:

''Questions:

(1) I noticed that the bulb outage light comes on with the

brakes applied…even though the three brake lamp bulbs seem

to function as designed. Could this point to the brake

light switch as the source of my problems, even though the

brake lights seem to function as designed?’’

Sounds as if you have resolved this problem by moving one of the
connectors while checking and it now is making better contact. The
bulb check units rely on a certain amount of current flow in the
circuit to validate it. If the bulbs are not of the correct
wattage or some connections are a bit corroded the bulb check unit
is not happy.

'(2) If not, or to do further diagnostics, how can I test the

other two switches you mention are in series?’

The only two switches that I think are relevant to your question
are the ‘‘brake switch’’ (NC unless the brake pedal is depressed) in
series with the ‘‘gear selector switch’’ (NO unless the gear selector
is in drive).

‘’(3) It sounds like the most common issue is the brake light

switch. If further testing is not feasible, would this be a

good time to order one and see if it fixes the cruise?’’

Lets be clear, there are two switches loosely called brake
switches. One is properly called the ‘‘brake switch’’ and the other
is properly called the ‘‘stop light switch’’. The ‘‘stop light
switch’’ is apparently working correctly if your brake stop lights
are working.

‘’…power but no ignition…car in drive’’

Please clarify - how do you have power if the ignition switch is
off? You must have the ignition ON - Posn 2 (do not start engine),
brake pedal not depressed, and the gear selector in Drive. If you
then do not have power at the YR wire at terminal 12 (you should
also have 12V at terminal 1) of the cruise control module, you have
a fault either at the ‘‘Brake Switch’’ in that circuit, or a fault
with the ‘‘gear selector switch’’. Refer to Fig. 21 component
location chart for the location of each. If you also do not have
12V at terminal 1, then you need to check upstream at connection 29.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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7

In reply to a message from lockheed sent Sat 25 May 2013:

The connection 29, for the switched 12v power, that I referred to
at the end of my last post, connects to Fuse No. 2 (5 amps) of the
left main fuse panel above the drivers knee bolster. Take the fuse
out and check it for continuity with your VOM. With that fuse in
place and the ignition ON -Posn 2, you should have 12V at the
cruise control module plug terminal one - Light Green Yellow stripe
(LGY). If not, then you have a wiring problem from the fuse panel
to the rest of the circuit.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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8

In reply to a message from lockheed sent Sat 25 May 2013:

Hi Lockheed,

Yes, by ignition on, I mean indent 2. Car is not started
but it has power…

Checked fuse continuity…it is good.

Just tried getting 12 V at the LGY wire, but no luck. In
fact, I don’t have 12 V at ANY of the pins that feed into
the cruise control module beneath the metal ‘‘pen’’ in front
of the passenger seat. I had the cruise button switched to
‘‘ON’’ if that matters.–
jstjagguy
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9

In reply to a message from jstjagguy sent Sat 25 May 2013:

Don’t like the sound of a wiring problem…as it must route
under the dash from the fuse bank to the CC module.

I wasn’t 100% on the units with my VOM…but I made sure by
testing the fuse under the hood that I learned had 12 V of
power with ignition at position 2 when fiddling with the
ABS…to make sure my units were correct.

Is this a common problem with these cars? What would you
check next?–
jstjagguy
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10

In reply to a message from jstjagguy sent Sat 25 May 2013:

''Just tried getting 12 V at the LGY wire, but no luck. In

fact, I don’t have 12 V at ANY of the pins that feed into

the cruise control module beneath the metal ‘‘pen’’ in front

of the passenger seat. I had the cruise button switched to

‘‘ON’’ if that matters.’’

Justin,

This is significant, and may be the root of your cruise control
problem. The cruise master switch is not a player in this issue -
it has no direct circuitry to a 12v source - see the schematic. Go
back to fuse #2 (5 amp) at the left main fuse panel. Remove the
fuse, Turn the ignition ON (posn2) and put the black lead of your
VOM to a good ground. Place your red lead of your VOM at one end
of the #2 fuse socket and then the other end - one of the ends
should have 12V. It doesn’t make any difference what you
found ‘‘under the hood’’ with the ignition on, one of the ends of
this #2 fuse holder must have 12V with the ignition on. If you
found 12V at one end, put the fuse back in and test for 12V at the
other end of the fuse holder. If you have 12V there, then drop the
fuse holder assembly and find the LGY wire from the #2 fuse holder
and test it for 12V. If you have 12V on the LGY wire, then again
probe the Cruise Module plug LGY terminal (#1). For each of the
steps above, let me know what you find. No need to (don’t) probe
any other pins of the cruise module plug for 12V.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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11

In reply to a message from lockheed sent Mon 27 May 2013:

The bulb outtage light WILL illuminate when the brakes are applied
if the ‘‘E’’ brake is even slightly engaged, make sure it is
completely released, pull it up then down.–
1986 XJS, 5.3 Litre V-12, 1997 XJ6L, 1974 Triumph TR-6
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12

In reply to a message from JT sent Mon 27 May 2013:

I re-tested this morning and here is what I found:

(1) I do have 12 V at the cruise control fuse.

(2) I mistakenly told you that I don’t have 12 V at the LGY
wire, when in fact I do have 12 V at the LGY plug at the
cruise control module…my apologies, I’m still learning
what a good ground is.

(3) However, I do NOT have 12 V at the YR red wire at
terminal 12. This was tested using the same ground in
(2)…so no chance for error on my part.

So I must have a fault at either the gear selector switch or
the brake switch, right?

Is the brake switch the thing that people have commonly had
trouble with in reference to the cruise on these cars? If
so, I’d like to order one today.

Also, I couldn’t see any such switch above the brake pedal,
but I may need to look a little harder…

If there are any other tests I can do to confirm that it is
the brake switch, I’d like to try them out.

Maybe check continuity of the brake light switch? Would
that tell me if the switch is good?

Thanks!–
jstjagguy
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13

In reply to a message from JT sent Mon 27 May 2013:

Lockheed, in response to a post by another user in 2012 that
referenced the same instructions that I used here, you said:

‘‘The comments that I made (and you are referring to) were
addressed to an individual who had installed a GM six
function electromechanical cruise control in his LT1 powered
XJ6 - the GM cruise control is now working perfectly. Those
comments are not applicable to the Jaguar cruise control.’’

I want to make sure that these tests are applicable to my
car with the Jaguar OEM system… I know you warned me at
the beginning that they might not be applicable, but they
seem to be.

Also, in the archives there is confusion on correct
terminology for these switches, I think.

People referred to the part that frequently causes trouble
with the cruise as the ‘‘brake light switch.’’ According to
the literature there is only a ‘‘brake switch’’ and a ‘‘stop
light switch’’ in this circuit. What further confuses the
matter is that they are apparently both on the brake pedal.

According to the electrical diagram, the part that may be
faulty here is the ‘‘brake switch’’ which I assume has nothing
to do with the actual brake lights. Is that correct? And
if so, is that the part that commonly goes bad and messes
with the cruise control system - or is the part that is
commonly faulty the ‘‘brake light switch?’’

Thanks,

Justin–
jstjagguy
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14

In reply to a message from jstjagguy sent Mon 27 May 2013:

From an earlier post in this thread:

‘’‘’(3) It sounds like the most common issue is the brake light

switch. If further testing is not feasible, would this be a

good time to order one and see if it fixes the cruise?‘’

Lets be clear, there are two switches loosely called brake

switches. One is properly called the ‘‘brake switch’’ and the other

is properly called the ‘‘stop light switch’’. The ''stop light

switch’’ is apparently working correctly if your brake stop lights

are working.‘’

If your brakes lights are working, the ‘‘brake light switch is OK’’.
You need to check the ‘‘brake switch’’ which is in series with the
gear selector switch which you should also check.

To find the ‘‘brake switch’’, you need to drop/remove the scuttle
above your knees and legs on the drivers side- just like you would
to look at the fuses, but completely remove it so you can get your
head down there and look up the brake pedal lever to see the
switches. You can identify the ‘‘brake switch’’ by finding the plug
with the LGY and the YR wires going to it. You will notice that
plug has four wires coming out of it - also a GB & B. We are only
interested in the LGR and the YR. If you are lucky, you will be
able to slide your red probe down into the plug a bit along side of
the LGR wire, and the black probe along side of the YR wire. If
you Read 12V with the brake pedal not depressed, the switch is
bad,if ‘‘0’’ Volts, then the switch is good. It may be easier to
just remove the switch and test it. If the switch is bad, replace
it. If it is good, then you will have to replace the ''gear
selector switch which is under the gear selector plate. You can
identify it by the color of the wires going to it as given by the
cruise control schematic.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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15

In reply to a message from lockheed sent Mon 27 May 2013:

Lockheed,Thanks for the info about the ‘‘control valve’’. I just
repaired my cruise control with a new bellows and repaired
broken wiring on the plugs to the unit, but I can’t keep speed
on an upgrade. Where do they hide the valve with the motor?
I’ve been following my vacume lines and I can’t seem to find
it.
Am I going to have to do a metered split of my vac or just
bypass the ‘‘recall vac switch’’? Thanks again EMG–
EMG
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16

In reply to a message from EMG sent Tue 28 May 2013:

Hi Lockheed,

‘‘It may be easier to
just remove the switch and test it.’’

I think I found the brake switch…there is not a whole lot
of space up there, so I think it will make the most sense to
remove and test.

How can I test the brake switch with the unit on the bench?

Thanks!–
jstjagguy
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17

In reply to a message from jstjagguy sent Tue 28 May 2013:

Hi Lockheed,

Got it out of the car…thanks for the guidance on finding
it. Why does the schematic not show the other two wires
coming and going from this part?

I’ve got it on the bench…how can I test it? I couldn’t
see a way to slide the probes down into the unit…it’s all
sealed up. Maybe it’s time to order one and see what happens?

Would like to test it first if possible.

Thanks!–
jstjagguy
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18

In reply to a message from jstjagguy sent Tue 28 May 2013:

In an effort to do this myself, I checked for continuity
(resistance test) at the terminals on the ends of the YR and
LGY wires with the brake switch removed.

When I pressed the switch in (as if brakes are applied) I
got 0 ohms, and when the switch was not pressed in (as if
the brakes are not applied) I got infinite resistance. Does
this tell me that the brake switch is okay?

Thanks.–
jstjagguy
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19

In reply to a message from jstjagguy sent Tue 28 May 2013:

‘‘Why does the schematic not show the other two wires coming and
going from this part?’’

Used to be two separate switches - don’t know when the switch was
made to a single dual function switch. As you will learn, Jaguar’s
wiring diagrams to not keep up with running changes in production.

''I’ve got it on the bench…how can I test it? I couldn’t

see a way to slide the probes down into the unit…it’s all

sealed up. Maybe it’s time to order one and see what happens?’’

Did you not disconnect a plug from it before you removed it, or
does it have a pigtail with the wires and a plug? I don’t know, I
have never seen it. Anyway, you should have terminals that the
plug connected to, or that connected the pigtail. Identify the
wire colors according to the schematic and identify the
corresponding connectors/terminals. Set you VOM to the Ohms
function and touch the tips of the probes to the
terminals/connectors of the terminals/connectors you want test.
You need to test the terminals for the LGY and the YR wires. Do not
push the switch plunger. As this switch is NC (according to the
schematic), you should read ‘‘0’’ or near 0 Ohms. If you read a lot
more or Infinite, replace the switch assembly. FYI, if you
read ‘‘0’’ or near 0 Ohms and you push the plunger, you should read
Infinite.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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20

In reply to a message from EMG sent Tue 28 May 2013:

‘‘Where do they hide the valve with the motor?’’

Don’t know, never had one apart or had any trouble so far. My guess
is that it is integral within the motor module. Well, I guess
that’s why they called that module a control valve - they figured
the electric pump motor contained therein was of lesser importance.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
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