Hi guys,

I need your help with "gearbox fault". I got the gearbox fault warning yesterday on my way to grocery. No limp mode. Still drives fine. I read a lot of posts here in the forum that this may be caused by wet TCM. I took it out today and found no sign of water leaking. I also read the code, which is P0778 (Pressure Control B / Electrical). What is the problem? Is it really about transmission? If so do I expect to buy a new car? BTW, it is a 2004 X type with 110K miles. I also did drain and fill of ATF three years ago. Have not got any issues until now. Thanks!

 

Jaguar list the following as potential causes of this code.

Transmission to TCM 2/4 Brake pressure solenoid circuit: open circuit, short circuit
Transmission internal 2/4 Brake pressure solenoid circuit: open circuit, short circuit
TCM Ground circuit: open circuit, high resistance
2/4 Brake pressure solenoid failure

So worst case looks like a 2/4 solenoid failure (Can be changed without removing transmission.)

You've got to hope its a bad ground connection - Black wire on Pin 9 on the TCM to ground at the base of the lefthand A post 3 or a damaged Green wire from Pin 3 on the TCM to the 2/4 solenoid in the transmission valve block.

 

I have a multimeter. How to measure it?

Could you please let me know how to change it? Thanks!

 

You need to carry out a range of tests as specified in this extract from JTIS:

P0778. 2/4 BRAKE DUTY PRESSURE CONTROL SOLENOID MALFUNCTION

CHECK THE 2/4 BRAKE DUTY PRESSURE CONTROL SOLENOID GROUND CIRCUIT. Disconnect the transmission electrical connector, (JB155). (The black 18 way connector to the transmission) Measure the resistance between pin 18 (Black wire) and GROUND. Is the resistance greater than 5 ohms? If No, go to A, if Yes go to B

A. CHECK THE 2/4 BRAKE DUTY PRESSURE CONTROL SOLENOID RESISTANCE. Measure its resistance between JB155, pin 16 and pin 18 at the transmission. Is the resistance 2.9 ohms? If No, INSTALL a new 2/4 brake duty pressure control solenoid. CLEAR the DTC. TEST the system for normal operation. If Yes, go to C.

B. CHECK THE 2/4 BRAKE DUTY PRESSURE CONTROL SOLENOID GROUND WIRE FOR CONTINUITY. Disconnect the TCM electrical connector (JB131). Measure the resistance between JB155, pin 18 and JB131, pin 17 (Black wire). Is the resistance greater than 5 ohms? REPAIR the high resistance circuit. CLEAR the DTC. TEST the system for normal operation.

C. CHECK THE 2/4 BRAKE DUTY PRESSURE CONTROL SOLENOID SIGNAL WIRE FOR CONTINUITY. Measure the resistance between JB155, pin 16 (Green) and JB131, pin 03 (Green). Is the resistance greater than 5 ohms? If so, REPAIR the high resistance circuit. CLEAR the DTC. TEST the system for normal operation.

 

I measured the resistance of JB155, the connector going into transmission. It seems that most of the resistance go beyond the values they should be. Especially, 1 and 2, 3 and 4, 5 and 6, 7 and 8, 18 and 9, 18 and 12 are infinite, meaning open. The weird thing is that I only got three codes, P0778, P1111 and P0778 pending. If all things went wrong, I should have got more codes, right?

I also checked all the wires of JB155, no damage found.

One more thing, my car is 2004, however it is produced in April 2004, so not sure it is X405 or X400. I heard that X405 has different electrical system than X400. I am not sure the values attached are for X400 or X405 since it only says 2004 Jaguar X type.

So now can we confirm that the problem is really inside the transmission, i.e., the valve body? What could the problem be? If so I will open the side pan and purchase solenoids. Thanks!

 

First, there are no wiring differences between early and late 2004MY as far as your problem is concerned.

When you're taking those resistance readings, are you taking them on the connector at the end of the wiring harness or at the socket on the transmission that it plugs into? Using my previous post, Checks B and C are from one end of the wiring harness to the other (at the TCM). Check A is done on the pins of the transmission itself.

All the resistances listed in your diagram are on the transmission socket - not not on the connector on the wiring. Does that help?

 

yeeran, something is up with your plug that you are making the measurements from. The big give-away for me is your 18 to ground check. That should be either a very low resistance (ie, under 2 ohms) or an open (greater than 20K). With it reading 18.1 ohms, this is telling me that you have either a bad set of leads or you are not on the correct connector.

Like was mentioned, you should be taking the resistances on the connector on the tranny itself. If you take them at the TCM plug end, this can lead to a little bit of confusion as you are playing with more wiring. Granted, there are times when this may be advantageous, especially if you are having issues getting to the tranny plug.

Another thing that I may recommend if you are dealing with the female end plug, wrap a piece of solid core wire around each probe and tape it in place with say a 1/2" of wire sticking out the end. This will allow you to reach into the plug to ensure you are getting a good connection. You can also use some short pieces of say a paper clip and slide them into the plug holes and measure from there.

I would also recommend looking on the plug face itself. You should see small numbers (they are only going to be but about 1/16" tall) on the end plugs just to make sure that you are getting on the correct pins. Remember, one end is going to be like the drawing above, but the mating end is going to be reversed. This is where those small numbers are going to pay off. Having a flashlight to shine on the end of the plug is going to be key. if you can't find the numbers, the we can do it by matching up wire colors. Write me and I can get you wire colors to look at.

 

Thanks for your reply.

All the readings I listed are from the socket on the transmission--18 male pins.

I understand Check A, B and C. B and C are to see if there are connection issues of the wiring harness themselves between TCM to JB155. Check A is to see the solenoid.

Then what is next? Really confusing.

 

Thanks for your reply.

1. I measured the resistance from the transmission end, 18 male pins.
2. What does GROUND really mean? Is it ground (earth or floor) or body frame of the car? I think it should be the latter. I measured pin 18 against transmission body and got 18.7 ohms. Between pin 18 and garage floor it is much higher, like open.

I also used a thin steel wire to measure the female pin and I noticed the tiny number you mentioned. Thanks!

Assuming the readings I got are reliable, where is the problem? The bad set of leads? Is it possible that the electrical system inside the transmission is completely messed up?

 

yeeran, when the term "ground" is used, it simply means that it is a common tie point for multiple wires. This normally also means that it is at a potential that is referred to as the zero or neutral state. But, this is not always the case. I deal with circuits where the "ground" is at a higher potential than the ground pin on the 3 prong plug that you plug into the wall. There are reasons for using each style of ground.

In the case of your car, the ground refers to essentially anything metal touching the body of the car. All of these parts (including the engine/tranny, driveshafts, axles) are physically touching each other and therefore are at the same electrical potential. Knowing what ground is important since the voltage that you read is relative to how high it is above the ground. In the case of a floating ground, if it is floating at say 5 volts above the earth ground, when I use a multimeter, measuring from the hot wire to the floating ground I would get say 12 VDC, but if I measured from the hot wire to earth ground, I would get 17 VDC.

IN the case of your car, the body is really a floating ground. There is nothing that is pulling any charge that is building up down to what the earth ground is. They do make special straps that you can bolt to the under side of the vehicle (ever seen those rubber straps that dangle on the ground when a car is parked? Those would be these) and it will pull the body of the car down to earth ground. The special straps have metal wires inside of them that keep the body of the car in contact with the ground and therefore prevent you from building up a static charge. Ever stepped out of a car on a cold day and when you touched the door handle got a big shock? These special straps stop that.

Now, back to the issue at hand. If the readings that you got are as you describe, then you have a wiring problem inside the tranny. Does the tranny need rebuilding? I don't think so. But, something has gotten loose and the wiring bundle has been damaged. Without cracking open the tranny, it is hard to say what has happened.

 

Update.

I had to admit that I made a mistake about the pin number. The Figure 10 in the picture above is WRONG. I measured the resistance again using the right pin numbers on the connector as Thermo said and confirmed that the 2/4 duty solenoid was the cause.

So today I changed 8 of total 9 solenoids because the last one cannot be removed without taking the whole valve body out since it's blocked by the connector. All resistance measured within range.

Added 6 qt ATF (what drained out was 6 qt) and cleared the code. Test drive in the neighborhood (speed below 25 MPH) and everything was fine.

Then went on roads and when speed >40 or 45 MPH got code P0375--5th gear ratio incorrect.

Did some research online. P0375 may be caused by low ATF level. Also I found in Jaguar Workshop manual that 8 liters ATF should be added after drain (the car sit for 1 week with drain plug removed so I think all fluid came out, which probably means the ATF was low before).

Here is the weird part.

Added 2 more qt ATF and did a test drive again. Still got the code. Then shifted the car in park with engine running and heard grinding noise from under the hood and the noise got louder and louder. This noise is very similar to what I got a couple of years ago when the ATF was low. I pressed the gas pedal a little bit. The engine or transmission made a harsh sound. AT THE SAME TIME, the check engine light suddenly went off on its own. Then the car had no gears--cannot shift into any gears, like it was always in neutral no matter it was actually in R or D. Shut the engine and plugged the scanner. No code except P1000. 10 mins later, started the engine and the car shift normally (did not risk driving above 40 MPH to avoid repeating the same thing) and the grinding noise was gone. Scanned the code again and still only got P1000. No CEL no "gearbox fault" message.

So what is the problem?
Where is the grinding noise from? Pump inside the transmission? Why did it happen after more ATF added?
Why did the CEL just go off? TCM relearned after 2 qt more ATF was added (maybe adjust pressure since more was inside)? If so why the transmission failed for a short time?

Thanks for any input!

 

yeeran, not sure what to tell you on this one. My initial reaction would be to simply take it for a test spin and see what happens. The P1000 code is simply there from the computers being reset. It needs to go through a drive cycle to clear things up. If any damage will occur due to what has been done, it has already happened. So, I don't see you really causing any more damage. I would say to stick close to home initially to see how things are going. But, from what you are describing, it may be that you simply got a little bit of crud somewhere and that was causing issues and it simply moved on and got caught in a screen or something of the like in the tranny (now is no longer an issue).

Maybe someone else will have some other advice for you.

 

Yeeran, the Jaguar approved method of getting the right level of fluid is a bit more awkward than just replacing what came out or just adding more! This is the most relevant extracts from Jaguar's instructions:

With the engine running and the foot brake applied, move the J-Gate shift selector through 'P-R-N-D-4-3-2' and back to the 'P' position to circulate the automatic transmission fluid until the temperature reaches 30 to 40°C (86 to 104°F)

When the automatic transmission fluid temperature reaches 35°C (95°F) check that the selector lever is in the 'P' position raise the vehicle.

With the engine running, remove the automatic transmission fluid level tube plug.

If the automatic transmission fluid does not come out of the transmission fluid level tube the automatic transmission fluid level is insufficient. If this is the case add the automatic transmission fluid in 0.5 litre units into the automatic transmission fluid charging pipe until the automatic transmission fluid comes out of the automatic transmission fluid level tube.

If the automatic transmission fluid does not come out of the transmission fluid level tube the automatic transmission fluid level is insufficient. If this is the case add the automatic transmission fluid in 0.5 litre units into the automatic transmission fluid charging pipe until the automatic transmission fluid comes out of the automatic transmission fluid level tube.

Allow the automatic transmission fluid to come out of the automatic transmission fluid level tube until the overflow stops at a temperature of no more than 40°C (104°F).

Make sure the automatic transmission fluid temperature does not exceed 40°C (104°F). If the automatic transmission fluid temperature does exceed 40°C (104°F) stop the automatic transmission fluid level check and allow the automatic transmission fluid to cool until the temperature reaches 30 to 40°C (86 to 104°F).

If when the automatic transmission fluid level plug is first removed and automatic transmission fluid comes out of the automatic transmission fluid level tube, allow the automatic transmission fluid to come out of the automatic transmission fluid level tube until the overflow stops at a temperature of no more than 40°C (104°F).

Install the transmission fluid level plug. Install the automatic transmission fluid charging pipe cap.

 

Update. I did some research online and found a common issue of JF506E transmission is that the high/reverse pistons could develop cracks and lead to no reverse, 3rd, 4th and 5th gears. So I opened the end cover of the transmission and pulled the high/reverse clutch assembly out. To my surprise, the bottom of the reverse drum was worn so badly that part of the metal was chipped away (see the first picture). There were burning marks/discoloration as well. The cover also had some wear, part of the groove was gone (not sure if you can tell from the picture).






Then I dissembled the assembly and found no cracks in pistons. Later I found the pistons were updated from 2003 model. Since mine is 2004 so this should not be a problem.

I did find hot spots/discoloration on high clutch steel plates. To me, it is not severe, two plates looks good and only one spot on each of the rest three plates. I also measured the thickness of friction plates and it is within range.

Now questions are:

1. How did a faulty solenoid lead to this issue? I know with P0778 code TCM will fix 4th gear, which means only 4th gear works (and reverse of course). I did drive around 10 miles after that and push the car to ramps by revving engine up. Not sure if it could lead to damage to clutch. According to the table below, high clutch is engaged during 3rd, 4th and 5th. Is it possible that the clutch can hold at 4th gear but slip at 5th gear? Is torque higher at 5th than at 4th? If so, could only 3 hot spots on steel plates lead to less gripping power?




I also noticed 2-4 brake (clutch) are engaged at 4th and 5th. I checked them, looked pretty good, no burning. Another thing is direct clutch. It only works at 5th gear. In theory, it may also cause no 5th gear. However, since it only works at 5th gear, the possibility of its going bad is much lower than high clutch which work at three gears. In addition, I cannot do anything to direct clutch since it cannot be accessed with transmission in car.

2. What could have caused the severe burning of the reverse drum?!! In comparison, the clutch plates inside were much less worn. I cannot understand. Really weird. If it is just a result rather than the root cause, then simply replacing it cannot solve the problem.

Any input would be much appreciated.

 

Any update Yeeran? I was just about to test my solenoids and today my car gave me the P0778, so I probably need that solenoid.

I have been having harsh shifts.

BTW, I changed out my reverse piston (which was not bad (on my 2002)) and my housing also looked beat up like that on the back.

The rover guys who also share the same transmission noticed the same thing...

 

I was not able to solve P0735 issue and I sold my car.

If you only have P0778 then just replace that solenoid only.

I found later that the "damage" of housing was normal, probably from the manufacturing process.

Good luck!

 

Thanks Yeeran.

I ordered that solenoid, and will change it out. Hopefully that is what was causing the harsh shifts before it threw the code.

I will also check the ohms, which I haven't done yet.

 

I was wondering where you were able to buy the solenoid. I have the same code showing up. I can't seem to find the part though.

 

https://www.carid.com/jaguar-x-type-...control-units/

https://www.rockauto.com/en/catalog/...+solenoid,8476

 

You sent me a few parts. Did you replacement all of them? Were you able to do it without removing the transmission and did it solve the problem?