Hi everybody,

I am new here and I already have a problem: My XJ81 has the transmission failure indicator light on when I turn on ignition, unlike the other indicator lights, it will not extinguish until I start the engine. When driving I actually can't notice any serious issues with the gearbox, it shifts all gears and it doesn't fell rough (unless you kick-down it). But there are two observations I have made in the past: when going constantly at about 50 to 60mph there is sometimes a little traction force disruption, just as if the torque converter clutch is about to open and close again (or vice versa). The second observation is that it doesn't stay in 2nd gear when selected manually, unless the transmission is cold, once it's up at temperature it will always shift up in 3rd gear (once speed is adequate).

I have read that it is possible to read error codes from the gearbox, but you either need a special service tool or you have to draw wires, which I don't feel confident with. Are there any other means of surrounding the root cause? How likely is it that my gearbox has a serious damage that requires an overhaul?

Thanks and kind regards
Oliver

 

The light being on until the engine starts is normal.

 

Thanks for your reply, that would be great!
But shouldn't it extinguish after a few a seconds just like all other dash lights? The way I understood it is that the indicator light remaining on means there is an error code stored. And it still being on with engine running would mean it is in limp mode. Am I wrong with this?

 

As long as it extinguishes when the engine starts you are OK. It does stay on longer than the other lights when ign is switched on on my car too but AFAIK that means nothing. Do not look for trouble where there is none!

 

Aha. Actually I never gave it much attention because usually that light is covered by the steering wheel from my seat position.

Please excuse my curiosity, but I have a few more questions: Does the light then mean it is still checking the transmission state? And it can't complete the check until the engine runs or does it just take longer than the other checks? And if it detected an issue the light would stay on when the engine is running?

Under what conditions would it go into limp mode? Under every conditions that causes the light to stay on or just under 'serious' issues?

 

Well, rejoiced too soon: made a little trip today and after maybe 40 miles the transmission light came on. I was going constantly at about 85mph, so no shifts whilst it came up. Anyway, the car drove as usual, it was still in 4th gear but would shift down to 3rd and 2nd if necessary, so no limp mode. But: when selecting 2nd manually it wouldn't go into second just as I had observed before. Then I parked the car, turned the engine off and then started it again: the light was gone again. I drove a few miles more until I was at home and the light didn't come back and even second gear worked again manually.

Originally I though the issue of not shifting into 2nd manually was caused by the transmission fluid heating up to normal operating temperature and maybe by a wrong fluid level, but now that the issue was gone after simply restarting the engine I think it's rather a different issue. Any ideas?

Thanks and best regards
Oliver

 

Made an inspection today trying to follow Jag-lovers ebook chapter on transmission failures but found out some things are a bit different on my car. Anyway I figured out that one of the connectors on the transmission itself was half-way out, so I pushed it back in (actually it didn't click so I am afraid its retaining mechanism is broken anyway) and hoped it would solve my issue, but it didn't as my test-drive did show.
But during my test-drive I made some interesting observations: the light comes on everytime I accelerate moderately in 4th gear from a constant speed. The first few times the light came on I was going at about 50mph and I also felt the TCC engaging/disengaging at the very same time so I thought the issue is somehow related to the TCC. But the last time it happended I was going at about 80mph when I started accelerating, this time the light came on without TCC being (tangibly) involved. So my next guess is the TPS, which seems to be a common source of failure.

But I am little confused, the only part having a connector on the V12 is the so called idle switch (#24). The throttle potentiometer (#4) has no (direct) wiring. Or am I wrong here at all?

 

I have a bit of input as an X305 owner, with the same transmission in my car. The major difference being that the XJ81 is not an OBD2 car and does not have the integration of the engine and transmission monitoring like the X305 has. So, I don't know how you would read codes from the XJ81 transmission. Anyway...

Easy things first: check the fluid level when hot. Make sure it is in the hot range on the stick, and keep in mind that the difference between high/low is only 6 oz of fluid. It is very important to get it right. Dexron III is the original spec (Valvoline blue jug). Some other newer fluids go off the original viscosity even though they may state it is backwards compatible (i.e. Dexron VI).

I agree that your slip while cruising is probably the Torque Converter Clutch. The 4L80E will set a code if it detects engine speed deviating from transmission speed past a certain point. I believe that while cruising (locked), if a speed difference is detected without the trans releasing the clutch, it would set a code (and the trans light). [This also might be why the trans light stays on before start until the engine is running, the trans wants to see the input (engine) speed. If so, that feature was designed out of the X305 system]

The TCC slip might not cause "limp" mode. If that happened you would only have reverse and 2nd (or 3rd) gears only, with harsh engagements, it is very noticeable. Whatever, the light and limp mode can be reset with an ignition cycle.

The TCC has a valve in the valve body of the transmission and also a valve in the oil pump assembly. It will probably take a transmission expert (an old guy who has worked on the 4L80E) to determine next steps. A rebuilt valve body is not a bad idea for a car of your (our) age. It can be done without transmission removal. A new oil pump assembly would mean transmission removal but it is accessible at the front of the actual gearbox housing. Of course the clutch disc itself is inside the torque converter.

I'll attach the Jaguar training guide if you want to go down a deep rabbit hole. It is pretty damn fascinating! It covers trans basics, ZF and GM Jag boxes.

 

Hi Richard,

thanks for your input.

I have already read through several sources (e.g. Supplement_7_4L80E-Transmission_Troubleshooting) and got some more insight, but I still have no clue if my issue is caused by some bad sensor, wiring or TCM or if it is a mechanical/hydraulical issue inside the transmission. My latest information is that you can read error codes from a port located on the battery tray in the trunk.
I also checked the fluid according to the procedure described in the referenced guide and I would say it is on the low allowed range, if not even below. But if I measure 5 times I get 5 different results. I already had filled up some more fluid in the past because I thought it was too low, but the next drive it blew fluid out of the vent, so I guess it's rather too high.

I did some more test-driving in the meantime with special regards to the TCC. Actually it should engage when going constantly at 50mph und this should be noticable by a drop of RPM and that is not the case! I only see a drop of RPM by 400 when I tip the brake pedal but I think that is normal and not related to the TCC. So my current guess is that when I accelerate after having driven at constant speed the TCM wants to disengage the TCC but since it is not engaged at all this fails and that's why the transmission warning light (TWL) is engaged. By I wonder if the TCM knows whether TCC is engaged or not, is there a sensor or another indicator? If there was one the TWL should already come when TCC is unsuccessfully engaged and not when it is about to be disengaged. And if it doesn't know whether TCC is engaged or not why does it engage TWL when it is trying to (unsuccessfully) disengage TCC?

Anyway I tried this several times at several speeds between 50 and 80 mph and it is always the same. The only difference is above ~70mph I do not feel the disruption I described in my previous post any more. And below 50mph I can accelerate without gettting a TWL. It also doesn't come in 2nd and 3rd gear. All of this is pointing towards a TCC issue in my opinion.

TCC not engaging or disengaging can have various causes like bad wiring, bad TCM, bad TCC solenoid or valves, fluid contamination, bad TCC, bad brake switch, bad turbine shaft seal. The brake switch would be the easiest thing to check ... if it was still available but it isn't. I don't know how to check the wiring or TCM because I do not even know where it sits. According to my latest information it should be in the trunk instead of below the dash.

Before going any further I think I need to have the DTCs read and see if they correspond to my observations regarding TCC. There is an old-established Jaguar Dealer in my region, they claim to have all the tools required for working on these old Jags but they are fully booked. Since my car is off the road for the winter season that would mean I have to be sitting until next spring with that uncertainty and that doesn't feel good and it keeps me from doing other work on the car.

 

Unlikely this old dealer would have the required software and hardware still operational as I know of no dealership that does, but maybe yours is one in a million?

I don't know how the manual describes checking the fluid, but what I do is drive car till fully warm, then while idling, move the shifter slowly through all positions ending up in park. Then take the reading.

 

I think I have to go there and talk to a service technician in order to get certainty, on the phone I only had an office assistant who couldn't give me detailed answers. But they do have a classics section where they work on all kinds of old Jags, they already helped me this spring with some specials tools nobody else had. If they do not have the necessary hard- and software for reading out the GM 4L80E, there should be a way of reading the fault codes by jump-wiring it. Maybe it's even possible to connect a GM Tech-2?

This afternoon I talked to someone who overhauls transmissions and he gave me advice to check the fluid level when cold as I complained having trouble to read the level when warm. When the fluid is cold, it's way above the cold-mark on the dip-stick. Maybe I should just try and remove some of the fluid just to see if it makes any difference.

 

I think it would be a good idea to figure out how to decode it before doing any work. Maybe there is a secret method to be found on the www. Or by finding someone who is familiar with the 4L80E specifically. They were common in the US in the 90s and 00s and there are still a lot of them around, at least in the US.

Usually you can feel the TCC engaging, but you reminded me that you can also feel it disengaging. So at steady speed, coast for a few seconds, tap the brake and you will see the revs drop slightly like you describe, and also you will feel engine braking is reduced. If you get that effect it would indicate that the TCC engages, but too weakly. It can't hold when you apply throttle to accelerate. Then it is a question of which component is causing the weak engagement. A code might help to narrow it down.

 

I sucked out some fluid today in order see if that makes a difference but I cannot tell for sure. It took a few miles more until I got the first TWL and lateron it didn't come every time I accelerated in 4th but maybe every second time. Could be related to lower (outside) temperatures or it could also be coincidence.

I will do another 'cold reading' tomorrow and then see if it makes sense to suck out even more fluid and then drive again. What I can tell is that I am still having bubbles in the fluid as you can see on the dipstick.

And I located the diagnostic port in the trunk, I think JDS is for Jaguar Diagnostic System, isn't it? There is a cap on it but it doesn't come off, don't know if there is a trick or if it just needs some more leverage.

 

You will need someone with a Jaguar PDU (!) unit. Nothing else will work.

 

Well I think it should at least be possible to flash out the DTCs by a jump wire. Even though I still don't completely understand how. And first of all I need to get that cap off.

I did another cold reading and according to that the fluid level still is way too high. But reading it hot yesterday it was way too low. I don't trust that thing at all.

EDIT: Found an interesting section in th transmission manual:

Torque converter clutch solenoid diagnostic monitoring
The TCM monitors the operation of the TCC solenoid. Using engine speed and transmission input speed, the TCM calculates the amount of torque converter clutch slip.

• If the TCM detects more than a 110 rpm difference between engine speed and transmission input speed in fourth gear when the TCC is commanded full ON with fluid temperature between 68˚ F and 286˚ F (20˚ C and 141˚ C) and the engine throttle angle is between 15% and 70%, DTC P0741 will flag. The TCM assumes the TCC solenoid valve is stuck OFF.
• If the TCC is OFF and the calculated slip is less than 15 rpm for more than 5 seconds with a throttle angle greater than 15%, the TCM assumes a stuck ON TCC solenoid valve and flags DTC P0742.
• The TCM also monitors the TCC signal voltage. A signal of 0V or 12V for more than 2 seconds indicates an open or short circuit. The TCM will flag DTC P0743.

In all cases the MIL will be activated.

Another section:
Transmission slippage diagnostic monitoring
The TCM compares engine speed to transmission output speed.

• If transmission output speed is more than 200 rpm above engine speed for 7 seconds when fourth gear is engaged with the torque converter clutch applied, fluid temperature between approximately 68˚ F – 286˚ F (20˚ C – 141˚ C), and the throttle open, the TCM will flag DTC P1739 and activate the MIL

According to my observations I would expect (or hope) to see DTC P0741 or 43, DTC P1739 would probably indicate a complete overhaul. That's gonna be interesting.

EDIT2:
Just noticed that these codes only apply to OBD II cars from 95 on. OBD I has different codes. And all OBD I codes related to TCC or driving in 4th gear should cause the limp home mode. That's strange.

 

If it comes down to taking a stab at something....

Replace the A and B shift solenoids and both speed sensors. Known for being problematic and causing weird symptoms.

Not too hateful in terms of cost and fully DIY-able...although a bit messy with all the ATF running into your armpits

As guesses go there are worse choices.

Cheers
DD

 

Not that easy on the V12. At least one side exhaust needs to come off in order to get the trans oil pan off. And 8 or 9 tiny ***** rolling off the top of the valve plate. But a perfect moment to replace the TCC solenoid and the pressure regulator;-)

I might repeat myself...read codes first, then measure line pressure before taking any measures. Might be a faulty TPS or else.

 

Exactly, when I had the transmission oil service they took off the right exhaust pipe and thereby cracked the rear exhaust manifold. Now that there is a new one in I won't release the oil pan until I have confidence that the cause is somewhere within the transmission itself. And possibly I won't undo the complete exhaust pipe but just cut it and join it together lateron. BTW: is it possible to remove the transmission leaving the engine in place or does it have to come out, too? Just in case it should indeed require a rebuild.

Actually I didn't know the checkballs were floating freely in the gearbox, sounds adventurous. I once was dealing with a faulty Mercedes transmission (722.6), it had a closed valve body so nothing could fall out. But to that none of my measures helped, finally the clutches came apart and could be found in the oil pan. So to say I just have a bad deja-vu.

 

I did some more testing with reduced fluid level and it seems the TWL comes a little less often, I need to accelerate for a few seconds longer until it comes up. And I made another observation: before I reduced the fluid level I sometimes had oscillating engine speed for a few seconds when coasting down to around 40mph and I probably felt the TCC trying to disengage what finally failed as engine speed remained at the low level. I sometimes thought it would try to shift down from 4th to 3rd, but usually it does not do this at 40mph. This is now gone with reduced fluid level, engine speed goes up just once and I think I feel the TCC disengage. So this would also mean TCC is not completely gone as I had suspected before.

 

As others have tried to point out the XJ40 & XJ81 used a special diagnostic system called a PDU and almost no dealers still have these units to really access the diagnostic codes present in the car. It is NOT possible to just stick jumpers into that diagnostic port down below the battery tray to get any useful information out of the system. If you have any doubts about this there is a VERY long thread here on this board with the title of "Jaguar PDU Manuals and Software" where folks have been discussing for years how to keep these old OEM PDU systems functional.