Hello!
Approximately two years ago I bought a wery cheap xjr that did not start (I know stupid but I like a challenge!). After getting it home it turned out to be a missaligned linear switch, so after some adjusting it started right up!

Now the real problem: The gearbox warning light is on and the engine is in limp home mode, after reading out codes it has the fault code P1777. Trying to erase it just instantly puts it back.
What I can understand it means that the gearbox can not tell the engine to relieve tourqe to be able to shift into next gear.

I have read around on this forum and diffrent others and most people have resolved this by replace the TCM, so I did that, did not work. I also read that the connector to the gearbox can be faulty. so I took it down and visualy inspected it. It looked fine no broken cables or pins. I also mesured the cables and they have good connections. The TPS connector could also be at fault. It is also fine. Messuring the signal from the TPS into the ECM and it send out correct signals. I have also checked and cleaned all the diffrent groundpoints.

Nothing have worked that should work according to diffrent threads so far, the light is still on. So now I'm running out of ideas. Had any of you this issue with your car and had it resolved? And in that case what did resolve the problem? I've started to suspect it is the ECM that has become wierd. But it is a bit to expensive to just buy another one to try and swap and se if it makes a differens. what do you think?

 

Certainly sounds like it's a failed TCM. In this thread there is mention of testing the voltage of the power reduction during shift pin.
https://forums.jag-lovers.com/t/x300...code/241430/27

 

I have a good used 1995 XJR TCM that you can have for the price of shipping. Check the part #,LAB2400CD. Also has harness connecter.

Larry Louton

 

There are a couple of Jaguar TSBs on the GM transmission you have

You should have the early version of the transmission mechanicals without the orange dot on the data plate

There was a TCM upgrade and without looking there may be a 3rd

See TSB # 08.2 - 01

JagRepair.com - Jaguar Repair Information Resource

 

Someone recently on a XJR discovered the TCM connector under the glove box was not seated fully

 

yeah all is pointing to being a faulty TCM but the thing is that I have swaped it out with another good used TCM and it did not fix the problem as it did for the user in that thread. Unless i got a case of bad luck and bought another faulty TCM.
I have checked the electrical continuinity between the moduels and that is fine. The tourqe reduction signal between the ECM and TCM also reads a steady 9.4 volts at idle but i have not tried to mesure it while driving. Maybe I should try that as the next step.

 

Couple of pages describing torque input and torque reduction request in engineering terms. You need to watch pin #7 and pin#12 as I see it. Pins #49 and #52 are of interest too.

Larry Louton

 

How is the quality of the trans fluid and the fluid level? The fluid level has to be on the top mark when the dipstick is too hot to touch. The trans in my car gave me all sorts of fits and giggles until I got it right. How many miles/KM on vehicle?

Larry Louton

 

Thank you!
That sounds interesting its the same part number as the replacement one I have.

 

Thank you! I will look into that

 

I have replaced the trans fluid and filter and the fluid should be att the right level. It is at the hot mark on the dipstick after running the transmisson to working temperature. But as the transmission is in limp home I have not been able to go trough all the gears to realy flush out the fluid i think. And the car has around 300000 km on the clock

 

With that many KM on the car, I wonder if you have an internal fault, like a shorted shift solenoid inside the transmission. Those can be tested and replaced just by dropping the pan, no need to further dismantle the transmission. It will be messy though, working with transmission fluid dripping on you isn't fun!

Take a look at some of Precision Transmission's youtube videos of the disassembly so you can see how it goes together. Here is one of the 4L80e.

 

The torque signal comparison I thought was a AC phase angle difference between the fore sensor and aft sensor as a synqro circuit

So a voltage value is not what you are looking for

I can be totally wrong in the automotive application but the propeller torque is the gauge you look at in the cockpit of a turboprop aircraft as well as the EGT as a limit

 

The torque reduction signal is 11.4V at idle and a ground pulse during shift.

 

You can test for short to ground or a open circuit from the TCM connecter, Without removing the oil pan. Another thing you can do is apply 12 volts to solenoid's and then apply a momentary ground. You can hear it click on a quiet day. Please forgive my notes on page.


Larry Louton

 

that could be a possibility, although if one of the solenoid were broken shouldnt it trigger more fault codes than just the p1777? We did check for electrical continunity for the internals via the transmission harness and also the resistans through the solenoids and the diffrent sensors and according to the electrical schematics I have for the car it looked good.

Thanks for the video alwas intresting to see how things are put together although after he removed the filter i was completly lost what all the canals and springs and stuff does it just lookedl like withcraft haha

 

Thats sounds alot easier than removing the oil pan. We did check for electrical continunity and resistans for the internals via the transmission harness and it looked ok. I will try to test the solenoids the way you described it. I guess if I dont hear a click one of the solenoids is broken right?

 

the 11.4V at idle I do have and I guess for checking the ground pulse I have to drive the car to se if it sends one?