I had started this in another thread, but since its not relevant to the original topic, I figured I'd start a new thread, which will also make the info more easily searchable for future users who need to troubleshoot.

Background story:

01 XJR, 124k miles, just brought it home. Worked perfectly during my test drive, trailered home 2 hours. Got my platers on it and went for my first drive, filled the tank and just enjoyed the feeling of my first Jag. Was going a steady 50-55 on a flat 2 lane road, wanted to give it some juice, stepped on the gas and didn't think it had much oomph for 370hp, tried to move the gear selector from D to 4 and found it seemed like it was locked out, backed off and then gave it a couple more pushes to the left, not trying to force it, and no good so I gave up, looked at the speedo and saw "RESTRICTED PERFORMANCE" and "GEARBOX FAULT" alternating on the display. Car felt like it was driving properly, but might have been stuck in whatever gear it was in at the time. Drove to my destination, shut it down to shot it off to my brother in law, when I restarted I had hoped it would reset itself, of course it did not. Wouldn't go out of first gear and I gently drove it home like that. Plugged in my reader, got the expected passenger side front O2 sensor code that I bought it with and also got a code P0705, "Transmission Range Sensor Circuit Malfunction (PRNDL Input)".

Little digging online and some advice here and it seems likley that this boils down to either the gear selector cable has worn and stretched a bit and I need to do a neutral adjustment procedure, or the dual linear switch, which is mounted to the shifter and tells the TCM what position the shifter is in may be faulty. Its also possible the cable has simply stretched to much and needs to be replaced.

So at this point I've got the entire center console out of the car (found 26 cents so far and a hairpin and I'm really surprised at how clean it is under there) and I'm doing my physical inspection. Cable lock nuts are tight, no obvious play, everything seems to move as I'd expect it...shifter feels maybe a bit notchy to me, but I've never been in a Jag before so I don't know if its normal or not. One thing I noticed is I'm able to move the shifter away from park maybe a half inch or so, which results in a beep...not sure if that sort of slop is normal for the J-Gate or if its an indicator of wear or possibly past abuse from a prior owner.

My plan is to do the cable adjustment for true neutral first and see if that clears anything up...maybe move to a replacement cable from that point.

 

The little bit of play, and beep when moving the shifter a bit out of P, is normal and also a good sign that shows your park safety microswitch is working.

If the cable adjustment doesn't do it, next thing could be to clean the linear selector. I had the same issue happen, right after replacing my transmission... took the circuit board out, scrubbed the exposed slide areas on the pcb with paper towel and deoxit contact cleaner, put a light bit of dielectric grease on them, and it seemed to work itself out after that.

 

Dual linear switch fault.

Info for you.

 

Nilanium beat me to it. I second what he said. The DL switch is mounted on the right side of the base of the J gate. Patience is key when doing this exploration to find out what happened. There’s many things that take a Phillips screwdriver, a magnet for dropped fasteners, either a 7/8”, 15/16” or 2 large adjustable wrenches if you need to adjust the shifter cable. You’ll need 2 of the same size wrenches. You basically need to remove the entire shifter assembly to clean up the DL switch as there’s several overlapping components. Be very careful with the P & N micro switches as the little metal tangs can take a flying leap. Good luck.

 

Thank you. By this you mean likely a replacement component or more likely troubleshooting to an adjustment to resolve? Waste of time to do the neutral calibration on the cable?

 

IF adjustment does not rectify the fault, then repair or replacement might be the answer.
Diagnosing problems is usually better/cheaper than throwing parts at the car BUT..............

Some people SUCK at diagnostics OR don't understand how things work.

Some are parts changers and others are diagnosticians. (pick one)

 

Well that didn't go quite right the first time around.

Did the neutral adjustment per the guide attached here, its for XK, but they're the same I beleive...found it in an old post in the x308 forum with an issue very similar to mine), thought I had it, but the clicks in the shift mechanism are a bit tricky to count off neutral seemed like the lever was almost perfectly vertical, as it appears in the illustrations...I clearly got it wrong though since the shifter now has to move all the way to D before it goes into neutral...oddly enough reverse seems like it engages spot on at the R notch. Try again tomorrow so I'm certain I've got this part right...obviously the gearbox fault warning is still displaying. Have to fix this bit properly before I move on to other troubleshooting.

Any suggestions beyond whats in the attached pdf for this specific step?

 

I prefer to diagnose more than toss parts at a problem, but some things do get beyond my abilities or toolbox.

Not sure if this is relevant, but I saw it in another post when I searched, my J-Gate has no illumination in any gear selection. I assume it should and its either disconnected or burnt out, but possibly a related symptom?

 

There is no red gear illumination when selected gear is not recongnized from the J-gate. Blue J gate back light seems to be always burnt.

 

As Vauxi said, no red LED illumination of the selected gear position means an error in the linear switch most likely, or a fault in the J-gate lighting module itself.

I don't remember exactly what the factory manual procedure states for the throttle cable adjustment, but the transmission shifter cable detents should be pretty distinct...

From how I remember doing it going off my intuition, the procedure went roughly like:
-Loosen both adjuster nuts
-Push shifter cable all the way into housing (so shifter is in its furthest back, or "D" position)
-Pull shifter cable out 1 click (for N)
-Align shift lever against N position in J-gate, so that the middle of the slop in the shift cable detent is in the little corner where the shift lever rests at N
-Tighten both adjuster nuts, ensuring adjustment isn't disturbed
-Check that shift lever behavior/alignment in P,R,N,D is good, going in both directions, adjust as needed
-Turn car on (no need to start engine), row through all positions a couple times, checking behavior is normal, no errors pop up, indicator LED's show properly

In any case, it sounds like it's most likely the linear switch gunked up or just gone bad... They can be hard to find the correct one though for replacements. Maybe worth asking forum members or checking the classifieds for parts cars, if you end up going that way

 

Pretty close, factory adjustment says
- Put gear selector in neutral
- loosten the retaining nuts on the shifter to allow max play
- Remove the cable from the trans lever
- move lever all the way to the rear and then go forward 2 clicks
- reattach cable underneath the car
- verify the gear selector is still in neutral and tighten the adjustment nuts down at the same time to preserve the length and cable setting.

I'm almost positive I messed up the last step, those nuts are difficult to get to move simultaneously and I'm fairly certain I don't have the front one down the threads far enough. Plan is to document my current starting point (thread counting) and I'm going to move it in one full turn and see how it affects the shifter. Should be relatively easy to get it back to where it originally was and eliminate my error and then I can get over to the switch and see about removing it and getting it cleaned up. I didn't read and think as carefully as I should have before I jumped to the cable adjustment idea.

Do Jags tend to suffer from cracked solder joints on circuit boards like so many other cars seemed to in the early 2000's?

I appreciate all the avice I'm getting here, thanks very much to everyone.

 

"Do Jags tend to suffer from cracked solder joints on circuit boards like so many other cars seemed to in the early 2000's?"

These ladies have lots of solder points, and their performance relies on not only the choice of solder but the quality of
the juncture. Damage at the solder joints can occur over time or suddenly. Several causes could explain failures at
these points. They include poor soldering, thermal cycles, tin whiskers or contamination. I am surprised, given the
high number of solder points that exist in these cars, solder point failure does not happen more often.

 

Progress of sorts.

Got the DL Switch out and apart, PRND side was pretty dirty, cleaned it with a q-tip and isopropyl alcohol and let it dry thoroughly. Did the same for the 4 3 2 contacts as well as the copper arms that touch them. Before and after photos are attached. Looked at the solder joints under magnification and saw no obvious cracking or components with all the smoke let out of them. After I reassembled the switch board into the housing I toned out P R N and D to verify that each one shorts to the center bus, it was really hard to reach the other grounds, was unsuccessful at testing those.

Reinstalled, think I got the cable adjusted properly as I now have drive in the D position, R is reverse, N is neutral.

Last step of the reinstall instructions for the switch say to leave it loose on the screws and the shifter in N and to move the switch fore and aft until N lights up, which it never does in my car so maybe the lights are bad...I basically tried to center it in its range of motion and tightened the screws. I'm not 100% sure I have the switch set corectly for the 4 3 2 connector, might need to just deinstall the whole thing and see how it all works with the little arm that comes out of the rotating shifter thing.

Edit: I just remembered that I did the see 3 light up in red briefly before I disassembled the switch, I don't beleive I was in 3rd on the gearshift at the time, but I did in fact see one selection light up...of course it was the wrong one and I don't know if this is useful information but I want to be accurate.





I am continuing to get the gearbox fault message and now I also have a gearbox overheating message, which is odd since the engine is cold and off. Likely a connector I disturbed or didn't do something right with the switch attachment? Or as unlikely as it seems, maybe an unrelated issue?

Guess next step is I'll remove the shoft assy and bring it inside for a thorough inspection and cleaning tongiht and try again tomorrow...which you guys said I'd probably have to do, just trying to check through one thing at a time...appreciate the advice and patience, I really do.

 

Correwct me if I'm wrong, but shouldn't there be two microswitches in here? One for park and one for neutral to allow starting in either selection?

Loks like it'll need a shave too. Yuck.

 

I've also noted that I have no reverse lights along with no gear selector lights. Starting to lean towards a bad dual linear switch (assuming that the backup lights are activated by the switch being in the reverse position), but wondering if there's a way to test it without a fancy Jag computer thing. Like if I have a 5v or 12v DC power source, can I use that and a multimeter to check the switch output...and by the same token, can I use that to also check my gear selector lights?

Found an old Jag Technical Bulletin for MY2000 that describes basically my issue, which is apparent spontaneous DTC P0705 and the restricted performance/gearbox fault messages and it say to just swap out the DL switch. I just want to be more sure before I spend $300 on a replacement part.

 

The more I think about it, the more I think my switch might be bad, but I'm not crazy about the indicator lights and backup lights not working and now the trans temp warning. Has me wondering if I'm chasing one problem or 3, 2 of which I might have created somehow.

Found a guy parting out a 2001 XJR and he is sending me the entire gearshift assembly with dual linear switch for $140 which he says is in working order. For that I feel comfortable spending to at least have all the spare parts I might need to determine if I have any bad components or not. Should hopefully be here Saturday and I can maybe get this sorted out so I can enjoy my new purchase.

 

XJ8 gets two microswitches, XJR only gets one.

That seems like a reasonable price for the assembly. Hate throwing parts at problems, but with old electronics it can sometimes be better than chasing ghosts, unless you happen to be an electrical engineer. Even then... the value of your time, etc.

I forget about the overheating message, I think it can be caused by a couple other bugs too.

The nastiness in the pivot isn't surprising, the brush material on that plastic disc the shifter travels through, falls out over time and falls down into that pivot.

 

Concerning the over temp warning on the Mercedes transmission.... there’s an electrical connector on the right, front, lower corner of the transmission just above the pan and behind a silver fiberglass (if yours is still there) panel.


These are notorious for ATF leaking inside where the male and female pins contact and can cause the overtemp warning you spoke of. You could invariably rotate the tang on that connector (CCW I believe) and see if there’s oil inside the pins. Your easiest bet is to spray the male and female pins with brake cleaner, throughly dry it off with compressed air and apply dielectric grease to the pins and reconnect. I’ve replaced one in the 10 years as a jag tech but, it’s also possible the conductor plate inside the transmission could be bad as the ATF temperature sensor is mounted to the board. I’d opt for investigating the electrical connector as a possibility after you get the shifter sorted out.

 

Ok, that helps clear it up a bit...but how does it start in neutral then? Is it taking info from the dual linear switch for neutral position, or is there yet another mechanism for it?

That was my reasoning as well. I've been hunting for a basic testing procedure to see if I could validate the dual linear switch with maybe a dc power supply and multimeter...thought I found what I needed, but it was for the AJ26 setup, not the AJ27 and the electrical connectors it describes are not the same on my car...so a spare complete assembly should give me ample spare parts to resolve my issue...since mine is apparently not missing a microswitch maybe I can just leave the shifter in place and hopefully its just the DL switch and I can keep the gearshift for spare parts...maybe the lighting will work on the new one too!

I'd really like to be able to test my existing gear selector lighting though...I don't like having multiple unknowns in a problem...maybe I can find a test for that and at least check the pinout on the board for resistance or apply 5v (or whatever it takes) to see if the LEDs are good or not.

 

Thanks Addicted2boost!

I had a random thought yesterday that I might have had the 4 3 2 selector in the wrong position on my dl switch and maybe that was the issue all along with a perfectly good DL switch...which given how it seems to operate, might have explained my original issue with it if it wasn't in the 4 position when I was driving it, it would explain the gearshift's reluctance to sliding over the the 4 position...could definitely see it getting "implausible" readings that way. Also I note that new switches come with a zip tie holding both sliders fully forward, so I opted to retry mounting it on the gearshift after verifying I had both sliders fully forward, fingers crossed I got it together, hooked up the battery and boom! same error. .

But the reason I'm relaying this story is to also note that the trans tempearture warning was no longer present at the time I had the key in and powered on, but not started...which is when it showed before.

That said, I'll locate that plug and inspect/clean it and apply some dielectric greas, as recommended. Evern if its not an actual problem, a little preventative maintenance can go a long way.

Waiting on shipping info from the guy with the spare shifter assy...I'm trying to avoid being impatient, but its hard...I chased the car's seller for 3 weeks + before I got to go check it out and now that I got it on the road, its going to end up being probably 2 weeks after my failsafe mode before I might get to really drive it.

Oh well, life with a modern classic car at this point, right?