[x300] Need some serious help guys thank you

OK I have a problem that is driving me bonkers, I have randomly
gotten the weird trans codes, sometimes it would go into limp mode,
sometimes a semi limp mode which will just lock out 1st and
overdrive, and then lately its been P0758 and P0753 which I know
are solenoids A and B. I read alot of other peoples expriences and
tried followin suit to see if it would help. I normally could just
turn the car off and clear the code and it would be fine for a
while. But I recently last day and half cant get the codes to go
away, I changed the trans fluid an used mobil 1 and new filter,
installed new trans mount with new springs and isolator, took off
all the trans connections and dielectric greased them, the internal
wiring harness in the trans looks like its been redone nicely and
seems good, I changed the solenoids both A and B with new ones from
GM, I have checked the fuse in L heel board #14 and its good, and I
checked the 5amp in the right heelboard and its good too but cant
get the codes to clear. I ordered a new external harness from Jag
but dont want to have to do it if thats not the cause any ideas
would be great. Hate trying to drive around with only 2nd gear and
reverse.

Car is a 1995 Jag XJR–
xjr0220
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In reply to a message from xjr0220 sent Mon 6 Dec 2010:

I’ve sent you some info privately, hope it helps!–
Steve, '95 XJR
Indianapolis, Indiana, United States
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In reply to a message from xjrguy sent Wed 8 Dec 2010:

OK thanks steve I emailed ya back I checked the ohms and both were
between 20.0 and 20.4. I replaced the external harness no change, I
dont know where to go from here I keep reading on th GM boards that
the ignition switch can be the cause does seem fesible on the jag??
Or would I not get power on the pins if that were the case?? Thanks
guys keep ideas coming–
xjr0220
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In reply to a message from xjr0220 sent Wed 8 Dec 2010:

Ok opened the tcm an it looks brand new it has zero corrosion and
looks new inside, checked pin 55 and has 12.64 volts 53 has zero
when ignition is off turn it on and it has 12.63 and pin 54 has a
good ground back to square one LOL. Still wondering if its the
internal harness even though its been redone it may have been done
wrong or they may not have gotten a solid connection for the wire
that connects to all the solenoids just weird I get the 2 codes
forever p0753 and p0758 and then after harness change and all it
goes too a p0743 and the other 2 codes are gone maybe I didnt clean
the contacts as good as I thought I will do that next and report
back what I find.–
xjr0220
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Ok so I’m now having the same exact issue… where did you start and have you had a resolve? Can you start with step one as in which plug youre testing, where it’s located and any other info you have would be amazing as this is my daily. I drove around with a scan tool and I can clear the code as I’m driving and it shifts normal, drives fine then about thirty seconds later right back to limp mode and I have a little insight but as I’ve never owned a jag I have no clue where the ecu or tcm would be located. Thank you so much in advance!!!

Clean your grounds and clean the wire harness into the transmission and check Frey wires

Where Is the tcm located?

Under the car go to the plug on the side of the transmission, you cant miss it.
The plug usually after now 25 years! gets a little crusty .
The ground was a big issue after awhile as well.
That main box which I never needed is behind the glove box correct?
But I would stick with the plug first.
Side note…ARE WE SURE YOUR FLUID LEVEL is up to max?
When the transmissions run low on fluid, you will get stalling and kookie issues.
Good luck, clean the plug put back with clear mercury /spark plug grease.
See what happens.
Lastly is there a MOUSE in the house?
gtjoey1314

Start with a tranny fluid flush. Let’s get that variable out of the way.

I had a nice red fluid, smelled fine. Started getting one of those codes and limp home mode…. I realized that I hadn’t changed that fluid in 60,000 miles! It looked good, so I never thought to change it I guess.

Anyways, took it to a shop, had the fluid flushed, problem solved.

Yeah I’ll start with the grounds then do a flush. I didn’t even think so do a flush for the same reason. My fluid is still pink as could be and doesn’t smell burnt and the car isn’t even at 100k so we shall see where it goes.

To me that sounds like the transmission fluid could be as old as 100,000 miles, and I’m not sure when you bought the car, so it can be as young as that mile marker, but I’m telling you, my fluid looked and smelled good…at 60,000 miles, but it sure wasn’t good.

That’s pretty wild. I will let you know the outcome.