The error code wheel of fortune continues - This time P1242

[JoergM]

Thought I start a new thread since he other one basically is more or less resolved.
After stitching up my headliner, I wanted to go for a test drive. Initially I thought all is good with the gears but just Saturday the problem came back.
Funny things are that I do not get a error code immidately.

Howerver, last Saturday I suddenly got a new error code P0703 - Brake switch Signal Circuit. And then today I got yet another P1242 - CAN Bus , Message missing from TCM.

After clearig the codes, nothing changed, I still was in Limp mode, but then I switched off parking solenoid or something like this in the WJ Diag app and then on again. Then the Jeep was moving again. I did not get far, since now the Jeep does not shift higher than the 1st gear, even in Drive.
Then the Limp mode came back again, and I could feel when I get close to idle, the Transmission wants to engage but then pops out, then wants to engage again, then pops out. Not sure what this could be.

What came to my mind, is that I might have too much transmission oil. As mentioned my dip stick was missing and I bought a OEM stick. Although it seems to work, I am not sure how precise this thing is. When I took the radiator apart I drained a bit of oil in the hoses as well as in the cooling reservoir, that was not more than 200ml or so. However I added at least another 1L to have the measure of the OEM dip stick in the middle. What are the symptoms of too much transmission oil. Could it be that this is the problem?

[RTB]

Try pulling the dipstick quickly after experiencing the problem. Never seen inside these gearboxes before, but could there be the potential that if you have excessively high oil level you could be foaming your oil?

I remember from years ago being told that if the oil is being stirred up by the spiny bits due to high level, the oil can foam or aerate. This would then possibly mess with all your solenoids and actuators in the box.

If you pull the dipstick the oil should be smooth and even. If it is bubbly, then it could be an issue.

Just a thought.

[RTB]

Since P1242 is a communications fault with the TCM, could it be that it has a locked fault that you can't clear, or even read with DiagPro?

I would unplug the TCM, clean up the plug pins, then plug it back in.

I had this trouble with my Airbag module and doing this cleared the fault. Has not come back since.

I'd be checking any earthing points on it too.

Comms faults are commonly caused by dodgy connections.

P1242 CAN BUS MESSAGE MISSING
P1242 CAN BUS MESSAGE MISSING FROM TCM
P1242 CAN BUS MUTE

TCM is probably locked in limp mode cause it isn't on the PCI bus.

[JeanLuke]

I've had the CAN bus error. It's the terminals on the CAN pair on the TCU. When you look at the plug you'll see a pair of wires that are twisted around each other on what looks like a separate part of the plug. Clean those terminals.

Sent from my moto g( plus using Tapatalk

[JoergM]

Thanks Rob and JeanLuke.

I will take the middle console apart anyway tomorrow since there is a lot of wiring for a aftermarket video system installed which I want to get rid off. This way I can have access to the TCM and do the cleansing.

I also will check again the fluid level of the Transmission. I really suspect that I have a touch too much. I even think of a oil exchange, since the oil did not really look so good anymore. Do you know from the top of your head how much these Trannies typically swallow? Cant really play the game "refill what you got out" since the measures might not be right. This way I can at least be sure that I am in the ball park.

[RTB]

I wouldn't bother trying to fill to the rated quantity.

It is almost impossible to drain all the oil out. Between the coolers, torque convertor, and various passageways, you will never get it all.

In the past when I have serviced transmissions, I would say at best I have been able to get 2/3 of the oil out. Never been able to drain the entire thing in one hit.

I had a heap of AV gear under the center console. Also took it all out.

[drover]

WG's never came with a dip stick..

Oil type may cause problems but just starting up overfull won't other than blowing out breather, too low will foam up and miss or stick changes....
Have a look at the right front of your gear box, there is a large electrical connector, unplug and have a look inside , if there's oil there, thats your problem, new plug is cheap and easy to replace but care is needed as it screws into a very expensive circuit board inside the gearbox... replace plug is available form Benz, cheaper and easier than any dealer.... I always used Penrite in my W5A580 tranny.... as well as in my 8HP70 now.

Otherwise disconnect battery and unplug the TCM and other magic boxes sometimes it works whether fully clearing memory or by ensuring better contacts I don't know.