Hi people.

Recently aquired a 1995 XJR with the GM 4L80E transmission, only had it a few weeks but on Friday the gearbox went into limp mode. The fault came back as shift solenoid B stuck P0756.

So first port of call as it was already on the to do list was new filter and fresh fluid, this got it out of limp mode temporarily but it is still going back into it although not as often and does seems slightly better.

Should I now search for a replacement solenoid? I am led to believe it is no longer available from Jaguar under part number JLM10966.

 

The transmission is the GM 4L80E pretty solid transmission. It has two shift solenoids on the valve body 1-2 and 2-3 shift easily obtained and inexpensive (about $20 US each). Changing them is also an easy job and within the capabilities of the DIYer. I helped my son change his 1-2, 2-3 shift solenoids in the 4T80E transmission in his 2003 Cadillac Seville STS. The 4T80E is the same transmission as yours except for a transverse installation. I do believe your trans. will have to be reset using the proper scan tool after new solenoids are installed. Note: there are also torque converter clutch solenoids which are another can of worms entirely.


Good luck!

 

Hi thanks for the encouragement, I have a scan tool already reset after I changed the fluid and filter but fault has come back. Do you reckon any solenoids listed for a GM 4L80E should do the job? My next challenge is to find a supplier of them here in the U.K. - I'll be making some phone calls when we're back at work Friday.

Seasons greetings!

 

Aaron, you don't mention that you flushed the transmission. If not, then just draining the pan and changing the filter will only remove about half the fluid or less. A significant amount is held in the torque converter. It will take about 4-5 fluid changes to 'dilute' the fluid to full strength. Just run the car a wee bit for a few miles between each change.

You will be surprised at how many problems it can solve and it is a lot cheaper than having transmission work done. You might want to change the filter again after the last fluid change.

 

Well yes of course this was my other thought don't know whether to persevere drive it some more and keep changing the fluid, can't believe how bad the stuff I took out was, has anyone had any experience with changing to dexron 6 rather than 3?

 

If the fluid looked that bad, I don't think I'd worry about changing brands, just changing fluids!!

Seriously, I'd go ahead and change the fluids at least 4 more times, 5 wouldn't hurt. Just drive it around the block to make sure the fluids mingle throughout the transmission between each change. It'll take you a good part of a day but I'd do it sooner rather than later.

BTW, did you happen to check the condition of the magnets in the pan?

 

Yep checked the magnets and not really any metal on them just what looked like Vaseline! I cleaned the pan up before putting it back on. I will go get myself a decent supply of atf and crack on with some more changes

 

It's a known fault with the XJR and XJ12 that the transmission harness is a bit short and can have internal wire breaks or intermittent contact if the harness is under strain as the rear transmission mount wears or sags. I think it's much more likely your problem lies in the wiring harness and/or the connection at the transmission, than an internal problem with the transmission itself.

 

Just an update now changed the atf a total of 3 times and added an additive and touch wood seems alright! Thanks for the advise on here

 

Ok so now things have gotten worse, fluid must have been changed about 5 times now and is looking nice and clean. I just fitted two new shift solenoids but this made no difference whatsoever! Very frustrating! It is now so bad that I can't put my foot down even half throttle without it going bananas ie bucking surging and sometimes stalling and so is pretty much un-drivable, only way to make progress is to be very gentle on the throttle but even then the transmission eventually goes into limp mode and I'm still getting P0756 shift solenoid b stuck/reduced performance and P1781 engine torque signal malfunction. Running out of ideas, time and patience!! Loom seems ok but not had a chance to do any continuity tests but the way it's been gradually getting worse and is consistently the same now leads me to believe it could be a mechanical issue?

 

I'm afraid that 'seems OK' isn't enough !

The harness is a known problem area. Condition must be confirmed, one way or the other, before doing anything else. IMHO.

Testing might not even be required. A very close visual examination might do the trick. The damage, if present, will probably be at the last few inches of the harness and/or at the connector pins.

Cheers
DD

 

Well yes you're right I need to at least rule it out trouble is just getting time to do it and just losing the will to go on with it! Only got it in December and I've been incredibly unlucky with it so far as the gearbox hasn't been the only thing to go wrong

 

I had this exact problem with my XJR about a year ago. Turned out to be two broken wires in the harness. Good luck finding which one.

 

Thanks for the encouragement you have re-energised me! How hard is it to get the plug off and the loom to one side to work on?

 

Right finally after having a holiday had time to check the wiring, it all checks out ok and now I only seem to get the one code which is P1781 engine torque signal malfunction. If I drive with REALLY gentle throttle it is ok but as soon as I apply more pressure it's as if it is misfiring really badly and it worse when I floor it to the point where once I release and come to a stop the car cuts out or cuts out when slowing to corner. Any ideas? Spark plugs are new

 

I think it would have to be a harness or ECM output issue.

Check the inputs/outputs at the TCM connector.

Pin 7 is the torque reduction request output (TCM tells ECM that a shift is about occur). This should be 11.5v at idle. The signal is then pulsed to ground when a shift is made.

Pin 11 is the throttle position input from the ECM to the TCM. Should be 1.4v at idle and 9v at full throttle

Pin 12 is the engine torque input from ECM to TCM. Should be 11.5v at idle decreasing with increased engine load.

 

Thanks Allan I'll check that next, don't want to give up on this but been without the Jag since christmas now as I don't get much time to look at it so getting pretty frustrated with it now.

 

As I mentioned before. This is the EXACT same problem that I had. The trans moves and one or two wires can break.

 

Would just like to thank everyone for their input . The XJR has been fixed for about 6 weeks now and it turned out the torque signal malfunction was being caused by dodgy spark plugs! Just before the trouble started I had fitted some non NGK iridium spark plugs that were supposedly designed for running on LPG, I have since put standard NGKs back in which I had luckily kept and then it behaved as normal and have since replaced these with NGKs iridium LPG plugs and all has been well for several weeks, but the gearbox is definitely better for all the changes to the fluid it has had!