Shortly after I bought my XJS back in May of 2010 the
transmission warning light came on and the power died down
and the transmission shifted hard when it changed gears.
The culprit was the little metal elbow that connects the
SAV from the back side of the A bank air filter box via a
short rubber vacuum hose had fallen out of the underside of
the A bank intake manifold and caused a vacuum leak. I
pressed the elbow back in the underside of the manifold and
the problem was solved until it fell out again so I put it
back in and ran some wire around the top of the manifold
and under the wire to keep it from happening again and that
worked.
A while after that I had the same problem with the
transmission light coming on with some hard shifts but not
nearly as bad. I noticed the SAV flopping around in its
grommet where it goes into that back of the air filter so I
bought a new grommet and that cleared it up for over a
year. Now the light comes on shortly after I head out so I
pull over and move the SAV around in it’s grommet and
restart and it’s fine until next time I head out. I figured
it was some air getting thru the SAV nipple and the grommet
so I wrapped some black electrical tape around the nipple
where it goes thru the grommet and then wrapped some black
electrical tape around the outside of the SAV and the ac
hose that runs along the air filter box just above and that
holds the SAV nice and stationary. After a while the trans
warning light started coming on again with the hard shifts
so I would pull over shut the motor down and wiggle the SAV
around a bit and that made it ok. But it still keeps doing
it. SO I tried something different. I just pull over, turn
off the engine and just restart it without even opening the
hood and the trans warning light is off and it just fine.
Seems every day I head out, about 1/2 a mile from the house
the warning light comes on, I shut down and restart and
it’s just fine…??? Any ideas from our experts here what
might be the cause? Maybe the connection of the SAV to the
bottom of the manifold has nothing to do with the problem
and just the act of turning off and then restarting the
engine clears up the problem but what could be causing
that???
Bruce–
94 xjs 6 liter conv.
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In reply to a message from skyman sent Sun 19 Apr 2015:
Hi Bruce:
I hate to tell you that the SAV has nothing to do with the
4L80e tranny issues. Every time this happens, you’ve got an
electronic input signal that is missing. For reading codes,
please see here:
As Dave says, your box goes into a limp mode, line pressure
increases and hard shifts. It resets itself upon turning
engine off until the signals are messed up again.
My thoughts:
Speed sensors should be cleaned and the connectors
checked.
TPS. The 6.0L V12 has a TPS with 6 wires – 3 for
fueling and 3 are inputs to the TCM. Your recent idle woes
lead me to believe that you’ve got flaky TPS – either the
pot itself or the harness.
To repeat – your electronic box will not flash a code
(light will not come) for reasons of vacuum leaks.
Steve–
The original message included these comments:
Shortly after I bought my XJS back in May of 2010 the
transmission warning light came on and the power died down
and the transmission shifted hard when it changed gears.
The culprit was the little metal elbow that connects the
SAV from the back side of the A bank air filter box via a
short rubber vacuum hose had fallen out of the underside of
the A bank intake manifold and caused a vacuum leak. I
pressed the elbow back in the underside of the manifold and
the problem was solved until it fell out again so I put it
back in and ran some wire around the top of the manifold
and under the wire to keep it from happening again and that
In reply to a message from sbobev sent Sun 19 Apr 2015:
This is common for our 4L80’s. Mine comes on about twice
a year…not enough to diagnose…yet! Whatever it is, it
is transient, so nothing to check by the time I get home.
Mine only happened cold and when in sport mode.
I agree that the SAV has nothing to do with it. The
concurrence was that the tranny speed sensor is the likely
issue, but nobody has confirmed that. It sounds like
yours is getting to be frequent enough to do a proper
diagnoses.–
John. '95 XJS 6.0L convertible. Southlake, TX
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In reply to a message from CJ95 sent Sun 19 Apr 2015:
John
Do you know where the tranny speed sensor is? If it’s
easily accessible perhaps just replacing it would be the
way to go.
Thanks
Bruce–
The original message included these comments:
concurrence was that the tranny speed sensor is the likely
issue, but nobody has confirmed that. It sounds like
Doug Dwyer had posted this information in the archives:
The speed sensors are external on the left side of the
transmission.
Easy access after the transmission mount is removed and the
trans lowered just a bit.
The A-B shift solenoids are at the rear of the valve body,
each held in with a single screw.
The TCC solenoid is at the front of the valve body and held
in with a spring clip thingy that is actually partially
concealed by its location in a slot.
It’s easy to pull the clip out but on installation of the
new solenoid a bit of wiggling is required to engage the
clip.
The fact that something is intermittent, to me, always
points to a aging sensor or a dirty connector.
Hope this helps.
Steve–
The original message included these comments:
In reply to a message from sbobev sent Mon 20 Apr 2015:
It sounds like a problem I had it goes to the limp mode and
you need to turn off the car and restart and it puts it
back in regular mode. I had a good friend with a tranny
shop look at mine. He said the speed sensor wires had done
the Jaguar insulation crumble and were shorting them out.
The sensors are GM parts with Jaguar plugs so he swapped
them out using the original plugs spliced on to the leads.
The big issue with this is he had to remove the tranny to
do this so he also did a full rebuild on the twenty year
old transmission. So it was costly but it now runs great
and no more limp modes, so if your car is a keeper that
might be the way to go. Mine got worse over time until it
was always doing it; especially when the engine was cold.
If you put your car in neutral and turn it off and on
quickly while the car is going you can reset the mode!–
DanS
columbus ga. usa, United States
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In reply to a message from DanS sent Mon 20 Apr 2015:
Dan:
Let’s not mix things here. Bruce’s car has 1/3 of your
mileage, transmission rebuilt is NOT needed.
As I said above, the sensors are external to the
transmission. If the transmission mont has not been done,
this is an excellent opportunity to do both – the
transmission should be supported by a stand, lower just a
bit – all done is situ.
A bad transmission mount could be a big contributor to the
harness needing attention. Dirt and grime, from the back of
the vee, blown into the transmission tunnel and smeared over
the sensors (very similar in operating principle to the CPS
and flywheel speed sensors) is another reason these problems
with limp-mode pop-up every so often.
Again, with regular fluid/filter change, the 4L80e box will
NOT need a rebuilt at 70,000 miles. Bruce, I hope you’re
reading.
Steve–
The original message included these comments:
It sounds like a problem I had it goes to the limp mode and
you need to turn off the car and restart and it puts it
back in regular mode. I had a good friend with a tranny
shop look at mine. He said the speed sensor wires had done
the Jaguar insulation crumble and were shorting them out.
The sensors are GM parts with Jaguar plugs so he swapped
them out using the original plugs spliced on to the leads.
The big issue with this is he had to remove the tranny to
do this so he also did a full rebuild on the twenty year
old transmission. So it was costly but it now runs great
and no more limp modes, so if your car is a keeper that
In reply to a message from sbobev sent Mon 20 Apr 2015:
Steve
Yep I’m reading. I researched the tranny mount a bit and it
looks kindof complicated. Doesn’t look anything like most
tranny mounts or motor mounts. It looks like a bunch of
parts…a spring and spring seats etc. Is this correct?–
The original message included these comments:
transmission. If the transmission mont has not been done,
this is an excellent opportunity to do both – the
transmission should be supported by a stand, lower just a
bit – all done is situ.
The yellow bush from the factory is gone by now.
Guaranteed. Your box is moving more than what it should.
Just like the bushes for the front shock absorbers (you’ve
done those, right?)
I think there is an upgraded aftermarket part. Get that one.
Steve–
The original message included these comments:
Yep I’m reading. I researched the tranny mount a bit and it
looks kindof complicated. Doesn’t look anything like most
tranny mounts or motor mounts. It looks like a bunch of
parts…a spring and spring seats etc. Is this correct?
In reply to a message from sbobev sent Mon 20 Apr 2015:
True I went over 200,000k this past month; the tranny was
done a few months ago. But it now has a complete fresh
rebuild and all new pickups. Also he thinks that my
electric lock-out in fourth had not been working for a long
time, it drops your RPM 200 at 80MPH to about 2600 RPM.
It just sounds like you are half way there just going after
the pick-ups, and mine is a long term keeper which is a
factor for me.
Dan–
The original message included these comments:
Let’s not mix things here. Bruce’s car has 1/3 of your
mileage, transmission rebuilt is NOT needed.
As I said above, the sensors are external to the
transmission. If the transmission mont has not been done,
In reply to a message from skyman sent Mon 20 Apr 2015:
Bruce:
The spring is likely fine, the seats ideally may have to be
replaced. The bush, however, unless previously replaced, is
gone. This was the first thing I did to my car – all fluids
and the trans. mount bush.
But, the best part of all…you may be able to put the new
bush without taking the whole thing apart.
The diagram shows and an allen screw and a washer at the
bottom, remove the and you’ll see the hole.
Clean (blow) whatever is left from the old bush and put the
new one in. Some soapy water may do the trick.
Steve–
The original message included these comments:
Is that the only part in the mount that wears out? Or do I
need to replace everything?
In reply to a message from sbobev sent Mon 20 Apr 2015:
Steve…I’ve been putting off the tranny mount because I couldn’t
get a good picture of what the new one looked like. Once again
you’ve explained it all! I’m going to order the parts right now,
and maybe even change those sensors too…
In reply to a message from skyman sent Tue 21 Apr 2015:
Steve
Sorry…please disregard last post. You already told me the
location. Senior moment??? Nah :>)LOL
Bruce–
The original message included these comments:
In reply to a message from skyman sent Tue 21 Apr 2015:
Steve,
Just re-reading. Your initial thread link above looks
like a partial. Is the flashing light for tranny
diagnostics on the TCM? I got that you short A8 into the
TCM to go into diagnostic mode, but don’t know where to
observe the flashing light for codes.–
John. '95 XJS 6.0L convertible. Southlake, TX
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In reply to a message from CJ95 sent Tue 21 Apr 2015:
John, info provided to me by the electronic guru Dave R.
(aka 540itouring). Look up his posts in the archives.
I have copied and pasted below some words from him:
The 4l80e I find easy to work on with electrical faults.
Remove the trans ecu and add a wire in pin location A8.
Refit the ecu and ground the wire while switching the
ignition on for about 2 seconds and disconnect wire from
ground. This will flash the gearbox light on the dash to
tell you the ERROR CODE which logged the fault. The codes
can also be cleared by grounding the wire from pin A8 for
approx 10 seconds with ignition on.
The codes are as follows and in two digits:
code 12 will flash twice as a heads up and then the fault
code(s)
14 Engine temp high
15 engine temp low
21 Throttle position High
22 Throttle position low
24 output speed low
28 Pressure Switch manifold
39 TCC Stuck off (slip)
53 System High Voltage
58 Transmission temp high
59 Transmission tem low
68 Overdrive ration fault
73 Force motor current out of spec
75 System volts low
81 Quad driver/Shift solenoid B fault
82 Quad driver Shift solenoid A fault
83 Quad driver TCC faulty voltage
85 undefined ration input to output (slip)
86 Shift solenoid B stuck on
87 Shift solenoid B stuck off.
Hope this helps.
Steve–
The original message included these comments:
Just re-reading. Your initial thread link above looks
like a partial. Is the flashing light for tranny
diagnostics on the TCM? I got that you short A8 into the
TCM to go into diagnostic mode, but don’t know where to
observe the flashing light for codes.
In reply to a message from sbobev sent Wed 22 Apr 2015:
So the dash light. Pretty cool. It sounds like a 2
person job unless you have very long arms. I ordered all
the sensors you listed. The whole lot is only $76 now.
Now I guess it would be smart to read the codes to see
which is actually the problem. I had no idea the errors
were being saved.
In reply to a message from DanS sent Mon 20 Apr 2015:
‘‘Also he thinks that my electric lock-out in fourth had not
been working for a long time, it drops your RPM 200 at
80MPH to about 2600 RPM.’’
‘‘lock-out’’? No, that would be the TCC (Torque Converter
Clutch) Lock-Up that would drop your engine speed 200 rpm @
80mph.–
lockheed 92 XJS Cpe/97 LT1/4L60E Miami FL
Austin, TX, United States
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