[xk8] Gearbox Symptoms and Diagnosis Help

XK8
1

Hi to all, ( this is a long post!)

I have a 1999 XK8 (same setup as X308) with a gearbox fault,
which I believe to be electronically, not mechanically
related. If you could point me in the right direction or to
an existing archive post would be greatly appreciated. Here
is a list of symptoms and fault codes:

Symptoms in order:

-start car and all is normal

-put in ‘‘D’’ and nothing happens

-revs up to 2000 rpm and a ‘‘clunk’’ occurs, and car is in
limp gear displaying ‘‘Transmission Fault’’

-will drive in limp gear

-switch over to to manual mode, up to ‘‘2’’, and back over to
‘‘D’’ and two things occur at once:

-the red LED lights on the J-Gate go out and never re-appear
and the readout now alternates with ‘‘Restricted Performance’’

-will still drive in limp gear

-shut off and restart, everything is perfectly normal,
select ‘‘D’’ and the whole thing starts all over again

Error Codes:

P0706-Rotary Switch and/or D-4 switch malfunction

P1722-Gear 2 Incorrect Ratio OR
transmission stall speed failure

P1797-Neutral Switch Circuit Malfunction OR
CAN TCM/ECM Circuit Malfunction

P1799- Hold Switch Circuit Malfunction

I have noticed that these codes usually point to one of four
things:

-The micro switches inside the J gate.

-The rotary switch attached to the gearbox.

-The rotary switch connector block on the engine side of the
bulkhead.

-The TCM.

I took the assembly partially apart to be able to see the
micro switches and they are all aligned properly.

Any advice or thoughts would be REALLY appreciated!!

Thanks,–
Thomas
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2

In reply to a message from jag170 sent Tue 9 Oct 2012:

i had a similar problem, have you checked that the operation of the
gear selector is not binding. Sometimes the ball joints on the
connections get dry and stop the selector engaging properly. You
could try to move the selector through it entire range of operation
once or twice before you start the car. I would also disconnect the
battery for a while to try and clear any codes.–
The original message included these comments:

I have a 1999 XK8 (same setup as X308) with a gearbox fault,
which I believe to be electronically, not mechanically
related. If you could point me in the right direction or to

–
Phil.D 3.8 etype, XKR, 4.2 MK2, XK150 FHC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

In reply to a message from jag170 sent Tue 9 Oct 2012:

Thomas
I occassionally get the gearbox fault after car has been parked for
a week or more and upon first time through the shifter sequence.
I’m sure it’s electrical because I can get the ‘‘fault’’ with engine
not running simply by stroking shifter through it’s motion. It
throws P0706 code ‘‘trans range sensor circuit’’ --Weird thing is if
car is used every day, No problem… I supect rotary switch is
dirty internally or the plug connector on the firewall needs
cleaning. Unfortunate thing is plug is near impossible to access to
clean or replace. For now I’m living with it.
See http://tinyurl.com/8hprnkt for more info.
I’m betting there are others with similar problem. Keep us posted
on any progress.
HTH
Rich–
rich neary
Statesville, North Carolina, United States
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4

In reply to a message from Phil.Dobson sent Wed 10 Oct 2012:

Thanks so much to the both of you for replying, I really
appreciate the feedback! I have also posted this in the X300
forum because the X308 generation XJ8’s have the same setup.

As far as it goes, I’ve cycled through the J-Gate many times
and that hasn’t affected it.

Also, I am very interested in checking the gear selector
binding properly. As I currently have the top cover off and
can see it, what do I look for? By going through the J-Gate
with the cover off, I believe that the ball joints are
working, but also noticed quite a bit of dusty debris and
(trimmed hair?!) from a previous owner of the car was in the
area if that might affect anything, but it didn’t look like
enough of an amount to really be hindering the system.

Upon further inspection, I noticed that when I switch from
neutral into drive, there is a VERY ever-so-slight forward
movement to the car. Even though I still think this is
electronic (might be a bad TCM), it also makes me lean
towards the A-drum malfunctioning. I am going to give the
car over to a trusted Jaguar specialist that I know with ex-
Jag dealer equipment to do a through diagnosis and see if we
get anywhere. I have not yet verified the level, or
condition of the transmission fluid, which he has the
special tool for.

How could I check the levels at home? A low level might
completely throw off the TCM.

Any advice or thoughts would be really appreciated!–
Thomas
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5

I have this exact problem occurred a few days ago 98 xk8 convertible, dealer wants to find a replacement gearbox. Did you find a solution to this problem