My 1999 XJR has begun exhibiting a Failsafe Engine Mode
fault message with associated yellow caution lamp after
driving for a few miles. Additionally, the cruise control
ceases functioning. Reading various Internet reports on
that fault, the brake switch seems to play a role in this
problem. I have a quality hand scanner but it doesn’t
return any DTC’s when the Failsafe fault occurs. Also the
engine does not have reduced performance. The one item my
scanner has detected seems to be a fault with the #2
downstream oxygen sensor. The scanner direct systems
reading mode shows zero output for the sensor but still no
DTC’s.
So, my question is, what scanner or laptop program is
needed to sort out this problem? Can an faulty oxygen
sensor cause the system to go into a Failsafe Engine Mode?
Twelve cylinders, 4 carbs… no sweat. Computer
controlled/monitored ‘‘Everything’’… UGH… Any and all
help from tech savvy owners/technicians will be most
appreciated.
Dick
'74 OTS
'99 XJR
1947 Stinson 108-1 ‘‘Voyager’’–
Growing Old is mandatory Growing Up is optional…
St. Cloud, Florida, United States
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In reply to a message from Dick Wells sent Tue 11 Oct 2016:
Had the same problem with my 98. Replaced the brake light
switch, which contains 2 small micro switches. From memory I
used a unit out of an X300 which was a straight swap but had
more robust micro switches.–
1988 XJS-V12, 1998 XJ8 V8, 1979 XJ6 Daimler
Sydney, Australia
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In reply to a message from Dick Wells sent Tue 11 Oct 2016:
If your handheld scanner can’t read extended manufacturer DTC
codes (which sounds like the case) then two of the lower priced
options are the AutoEnginuity software for PC and the Autel
Maxidas DS708.
These are still relatively expensive options. I haven’t tried
the AutoEnginuity software but I believe others have here with
success. The Autel DS708 is resold by Harbor Freight at a
relatively attractive price compared to other resellers, and
works well. I used it to diagnose the notorious ABS cold-solder
problem as well as my fail-safe problem (which turned out to be
the throttle body, as I didn’t have cruise control problems.)
The AutoEnginuity package has a better interface thanks to
having a full PC screen to work with, but the DS708 supports
dozens of car makes out of the box with 1 year of included
updates (AutoEnginuity is make specific last I recall, so if
you want to scan other makes of cars you have to pay.)
If you don’t have other OBD-II cars to use this on, you could
pay a dealer or independent shop to do a one-time scan.
Personally, the Autel unit has more than paid for itself just
isolating and fixing the ABS problem alone. Throw in the
throttle body problem and I’ve avoided paying nearly what the
car is worth (at standard shop rates.)
To be honest, the older cars have subtle problems like this or
worse - they just don’t tell you about them. But the fail-safe
mode is a really bad implementation. It had the habit of
popping up just when I hit the freeway, which I thought was
very dangerous for a fault that didn’t actually put the engine
in dire peril.–
The original message included these comments:
problem. I have a quality hand scanner but it doesn’t
return any DTC’s when the Failsafe fault occurs. Also the
engine does not have reduced performance. The one item my
scanner has detected seems to be a fault with the #2
downstream oxygen sensor. The scanner direct systems
reading mode shows zero output for the sensor but still no
DTC’s.
So, my question is, what scanner or laptop program is
needed to sort out this problem? Can an faulty oxygen
In reply to a message from bdragon sent Wed 12 Oct 2016:
Thanks to all for replaying to my help request. Great
community.
David, thanks for the specific recommendations for
scanners. I’ll check them out. I feel there may be other
codes hiding that I’m just not aware of. Every now and
then I get intermittent faults which seems to disappear
without intervention.
Best to all and
Happy Motoring,
Dick
'74 OTS
'99 XJr
1947 Stinson 108-1 ‘‘Voyager’’–
The original message included these comments:
These are still relatively expensive options. I haven’t tried
the AutoEnginuity software but I believe others have here with
success. The Autel DS708 is resold by Harbor Freight at a
relatively attractive price compared to other resellers, and
problem as well as my fail-safe problem (which turned out to be
the throttle body, as I didn’t have cruise control problems.)
The AutoEnginuity package has a better interface thanks to
dozens of car makes out of the box with 1 year of included
updates (AutoEnginuity is make specific last I recall, so if
you want to scan other makes of cars you have to pay.)
In reply to a message from Dick Wells sent Tue 11 Oct 2016:
To All,
Update on Failsafe Engine Mode fault. Having owned a slew
of Jaguars (mostly E-types) over the past 40 plus years
today I’ve come across the most insane design configuration
Jaguar has ever produced (IMHO). I’m speaking of mounting
of the Brake Switch. Decided to removed the assembly to
clean the micro switches. Getting it out was a definite
chore but re-installation was just plain nasthy!!! Wonder
if Jaguar ever requires it’s designers to perform parts
swaps BEFORE putting the vehicle into production???
Slight progress. Found the two micro switches are sealed
units. Spraying with contact cleaner doesn’t penetrate to
the switch inside. So really all one can do is spray the
switch push on connector ends. That’s what I did. That
seemed to solve the Failsafe Engine Mode fault and the
cruise control light now stays on. Tried the cruise
control. It worked once but refused to engage after
numerous further attempts. Now some other path to
investigate.
Here’s my take on everything so far. Don’t waste time
trying to spray contact cleaner into the micro switches.
They’re sealed. Instead, remove the 4-wire connector and
spray both parts then reassemble. If the fault still exist
then REPLACE the switch assembly with a new one. Really bad
design from a maintenance stand point.
Will report back when I sort out the cruise control problem.
Also, thought I had another problem. The AJ26 super charged
engine would not rev higher that 3,000 rpm while parked.
Discovered there’s a 3,000 rpm rev limiter while in park or
neutral. Oh well, Time to hit the pool and reflect back on
all this.
Dick
'74 OTS
'99 XJR
1947 Stinson 108-1 ‘‘Voyager’’–
Growing Old is mandatory Growing Up is optional…
St. Cloud, Florida, United States
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In reply to a message from Dick Wells sent Tue 18 Oct 2016:
I would just replace the switch. I replaced mine awhile back and
I don’t recall it being that expensive. With the contortions
required to get the switch in and out, I sure as heck didn’t want
to have to do it twice.–
X308 1999 XJR 4.0L, 02 BMW M Roadster, 02 GMC Sierra
Middlebury, IN, United States
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In reply to a message from Mike 99 XJR sent Wed 19 Oct 2016:
Mike,
Your recommendation is right on point. After my short-lived
elated joy the Failsafe Engine Mode fault reappeared.
Before it returned the cruise control would not engage. The
cruise control switch lamp stayed illuminated but the system
would not engage. Drove for a 40 mile test drive. Nearing
the end the Fault returned and the cruise control light went
out. Time to replace the switch. Also, just can’t get
around it - need to purchase the costly diagnostic computer
to read the codes my OBD II handheld doesn’t!
Wish me luck… Will post switch replacement results.
Dick
'74 OTS
'99 XJR
1947 Stinson 108-1 ‘‘Voyager’’–
The original message included these comments:
I would just replace the switch. I replaced mine awhile back and
I don’t recall it being that expensive. With the contortions
required to get the switch in and out, I sure as heck didn’t want
to have to do it twice.
In reply to a message from Dick Wells sent Wed 19 Oct 2016:
I dug back through my files.
The part number for the stoplamp switch on my 1999 XJR was
LNB6420BB. I see I paid $58.70 for it in 2011. Inflation has
nearly doubled the price to $112.94.
The best place I’ve found for most parts online is Jaguar of
Las Vegas. www.jaguarlasvegasparts.com (No affiliation)
I can’t recall your exact year and model, so make sure this is
the right part for your car.–
X308 1999 XJR 4.0L, 02 BMW M Roadster, 02 GMC Sierra
Middlebury, IN, United States
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In reply to a message from Mike 99 XJR sent Wed 19 Oct 2016:
Mike,
Again, thanks for the additional information and link. My
XJR is also a 1999 model. Since you have a like car would
you know if the rear lower shock rubber mounts can be
replaced without removing the shock? I have one that’s
started to klunk when drive over a bump in the road.
Without a lift if I have to remove the shock that’s really
going to be PITA!!! Any advice or suggestion?
Thanks again,
Dick
'74 OTS
'99 XJR
1947 Stinson 108-1 ‘‘Voyager’’–
The original message included these comments:
The part number for the stoplamp switch on my 1999 XJR was
LNB6420BB. I see I paid $58.70 for it in 2011. Inflation has
nearly doubled the price to $112.94.
In reply to a message from Dick Wells sent Wed 19 Oct 2016:
Unfortunately I don’t know the answer to that. You might try
posting that as a new question here in the forum. I’m sure there
is someone here who knows.
Best of luck.–
The original message included these comments:
XJR is also a 1999 model. Since you have a like car would
you know if the rear lower shock rubber mounts can be
replaced without removing the shock? I have one that’s
In reply to a message from Dick Wells sent Tue 11 Oct 2016:
Hello Dick,
I had the same problem recently with my 1998 Sovereign.
Checked the brake pedal switch as I was told this is normally
the cause, not this time as switch is good. An in-depth check
of the cruise system pointed towards a problem at the throttle
body. Nothing wrong here as TB is brand new. I recalled a
problem from my old series III where there was a leak in a
vacuum pipe which stopped the cruise from working so checked
this. Sure enough the problem was vacuum. On the top of the
TB the vacuum pipe connects using a right angled rubber
fitting, this had a small split thereby allowing air in and
dropping the vacuum. Replaced the rubber elbow and problem
solved. Pennies not pounds.
Always worth checking the cheap bits first.
Barrie–
The original message included these comments:
My 1999 XJR has begun exhibiting a Failsafe Engine Mode
fault message with associated yellow caution lamp after
driving for a few miles. Additionally, the cruise control
ceases functioning. Reading various Internet reports on
that fault, the brake switch seems to play a role in this
In reply to a message from Dick Wells sent Tue 18 Oct 2016:
Hello All,
Second update to my Failsafe Engine Mode fault. Sourced a
used brake switch (LNB6420BB) from a local donor car. On
examination I noted a small wear groove on the plastic
pivot arm that rest against the metal brake pedal arm.
Checked both micro switches and they were fine. Decided
to fill the groove with clear epoxy and let it set for 24
hours. Once set I surface filed the epoxy level with the
rest of the arm face.
Next I removed my original brake switch. Examination
revealed the same wear groove. Installed the donor
switch. Fingers cross, went for a test drive. Cruise
control worked normally and fault display disappeared.
The switch also has a ratcheting mechanism which I guess
is for fine self-adjustment on installation.
Will refurbish the original switch and re-install to see
if it also will function correctly. Will report results
when I complete the test. Also will not fill in the
groove, just open up the self-adjuster before
installation.
So, it appears the switch may be failing due to plastic to
metal wear, not electrical component failure. The two
Cherry micro switches are sealed units. They cannot be
cleaned. The one other thing I did to the donor switch
was re-solder the micro switch mounting points on the
circuit board. Don’t think that did much of anything but
will not re-solder the original.
Pictures to follow if I can upload them.
Now much sweeter motoring,
Dick
'74 OTS
'99 XJR
1947 Stinson 108-1 ‘‘Voyager’’–
Growing Old is mandatory Growing Up is optional…
St. Cloud, Florida, United States
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In reply to a message from Dick Wells sent Mon 31 Oct 2016:
Glad to hear you got it sorted out!
Unfortunately mine must have heard us talking about this and it
decided this would be a good time to fail also. Can’t decide if I
want to do this myself again or have my independent do it. I
wonder if the problem with mine is the plastic wearing also. It’s
been 5 years and a little over 20,000 miles since I replaced it.
Hmmm… the original lasted 12 years and 131,000 miles.–
1999 XJR, 02 BMW M Roadster, 02 GMC Sierra, 2013 XJL
Middlebury, IN, United States
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In reply to a message from Dick Wells sent Mon 31 Oct 2016:
This sounds very interesting indeed. I can’t wait for the
results of the control-check of the original switch!
I have also got a second switch (used) and had no
improvement upon fitting that. It stands to reason that the
‘‘new’’ one may have been replaced for the same reason, and
actually have the same fault…
In reply to a message from Bard Thomas Hesvik sent Fri 4 Nov 2016:
I had the switch problem with my 1998 Sovereign at 125K miles
and after being told a new one was going to be around �50 I
opted for a ‘‘tested used’’ unit �20.
Great, worked straight away no problems then without warning at
around 100 MPH ‘‘fail safe’’ lights up and car starts slowing,
does not look good when you are overtaking a BMW on an
autobahn. The rest of that trip was manual throttle which is
not cheap and 500 miles is a long way.
Got home and bought another ‘‘tested used’’ which only lasted
about 250 Miles. Decided to bite the bullet, bought a new
switch.
I am now 20K into the new switch and no issues, I can still
hear the micro-switches operating when I press the pedal which
I never did with the others. (Apparently because of the layout
it is possible to hear the micro-switches operate, if you don’t
have the windows open, music playing or passengers talking).
The thing with getting ‘‘tested used’’ is you don’t know how old
it is mileage wise so you could be buying into imminent
failure.
Moral of the story, if the original switch lasted around 120K
before failure �50 is not so expensive to replace it after all.–
The original message included these comments:
I have also got a second switch (used) and had no
improvement upon fitting that. It stands to reason that the
In reply to a message from Mike 99 XJR sent Thu 3 Nov 2016:
To All:
Installed the original switch with the adjustment opened
up slightly. Works fine so far (2 weeks). If the fault
returns I’ve decided to bond a small strip of shim stock
to the pivot arm face to stop the wear. so far, so good.
Dick
'74 OTS
'99 XJR
1947 Stinson 1081-1 ‘‘Voyager’’–
Growing Old is mandatory Growing Up is optional…
St. Cloud, Florida, United States
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LNB6420BB Brake Switch as removed from the car. Wondered what the spring mechanism was for. Determined it is an adjustment feature. Micro switches tested good and are sealed units which cannot be cleaned with contact cleaner.
Black smudge on arm face is where brake pedal contacts the switch. Plastic switch, metal brake arm results in micro groove in plastic face. Filled with epoxy and sanded flat before reinstalling.
Opening up the adjuster cam allows the switch to activate quicker on brake pedal application. This fixed the Failsafe Engine Mode and Cruise Control failure.
