Hey guys:
This is my first official post on this forum. I've got a '91 XJ40 base sedan with 82K miles. Here's the problem. About 15% of the time, my car will not shift out of first gear. I've cleaned/inspected the rotary switch, done the tranny fluid (although the filter will be done in a couple of weeks), & replaced the tranny relay. I've got a Throttle Position Sensor (TPS) ready to replace, as I know that the tranny is 'informed' when to shift by the TPS and they tend to get dirty and clogged with gunk. The shop manual suggests a bad valve or solenoid in the tranny itself, although I'm still inclined to think something non-mechanical because of the flawless and smooth performance all the rest of the time.

Here's my latest, and I think important, observation. When my car won't upshift, the gear indicator is illuminated "N". P, R, and N will illuminate, but D, 2, and 3 will not. The car will go into drive (low gear only) but will indicate that it is in N. I can only see one post about a similar occurrence buried in the recesses of this forum, but with no real solution offered.

A couple more things. It seems to happen more on hot days, or perhaps only when the cabin is hot?? Letting the car sit for a while usually returns things to normal. Sometimes the car will begin working normally mid-drive, complete with "D" illuminating. If it doesn't act up immediately at start up, it won't misbehave during that trip.

I'm beginning to think something to do with the control module? But I understand that is pretty rare. I would deeply appreciate any ideas you have - especially if you have had or seen this problem before. Thanks! Scott

 

Hi Scott,
Sorry, I won't be able to help you a bit. You're way ahead of me ... I haven't even got my XJ40 running yet.

I had two reasons for posting:
1) To let you know someone was paying attention. This isn't the fastest moving forum I've ever been on, but there are some sharp folks here, and I'm sure someone will be able to help you.
2)To congratulate you for stating a complex problem in a coherent manner. Seems like any sort of grasp of any language is rapidly becoming a lost art.
(uh, u now whut i meen?)

Good luck!

 

Thanks, Retro, if anything, for the moral support! I'd really love to find a solution for this gear indicator/transmission problem because in every other respect this is a really great and clean car.

Any ideas out there?
Cheers, Scott

 

Scott,
While I'm not sure about the gear indicator lights and upshifting issues being linked together, I'm a big fan of "correlation isn't necessarily causation."
Although I do agree that the gear indicator light malfunction is a very important observation while you’re also having shifting issues.
And not being an expert here I can only mention a few things I’d do if I was in your position. I may look at taking a multi meter to anything related to either system (electrical/transmission). Honestly I multi meter the hell out of everything when I have an issue and often hit pay dirt. I’d probably get in there and put my eyes on the shifting cable, also checking the neutral start/back-up light switch.
But again checking the shift cable is one of the best places to start. Speaking of starting … will the car start in other gears besides Park? That could be another clue of shifting cable issues, but I’ve seen it before when the gear indicator is pointing to the wrong gear (in Kentucky we just drive it anyway and don’t fix it, we get tired of driving in “D” all the time).
But I’d go ahead and replace that TPS before I did anything. And remove the battery cable for several minutes to let that little tranny microprocessor “clear it’s mind”. Plug it all back in and go from there.
And you said you’ve replaced the relay and inspected the rotary switch but did you also look at the transmission electrical connector?
So I’ve exhausted the tiny bit of knowledge I have. It’s limited and I’m not a professional auto mechanic by any means. Sounds like you may have even done most of this already.
Good luck!

 

Gents:
(and thanks to Nathan for his suggestions - taken to heart)
Here's the update on my transmission problem. After more reading, I went after the red herring of thinking the transmission decoder module may be to blame. I bought a used replacement, swapped it out (hard on the back to get after those dash components), and the car ran perfectly... until today. As I came to a stop - fortuitously on the way to a master Jag mechanic in a nearby town! - the car 'slipped' into neutral: that is to say, 'N' illuminated even though "D" was selected giving me power in low gear only. Within moments, it illuminated "D" again and we were off to the races. This was the first time his has happened to me whilst driving. Clearly the decoder module was not the problem. Today was also a very mild day, thus dismissing the notion that heat or humidity has anything to do with it.

I explained all this to my mechanic, who did my tranny filter today and inspected cables, etc. His impression is that this fault is the result of a flaky rotary switch/gear selector module on the side of the transmission. I'm growing to agree with him, but thought I'd shake the trees a bit more for ideas before I plunk down some neat cash for a replacement. I should say, I did inspect the rotary switch this spring and it looked good visually. But I didn't test it electrically in any way.

Any other ideas?

 

It has been a few months since my mechanic replaced the rotary switch on my '91 with a used part purchased from Jagbits (here's a shout out to the good guys in Michigan!) in hopes of solving the problem described above. The fault has not reoccurred, and enough time has passed for me to ever-so-reluctantly call this one 'solved.' It was a weird fault, and I talked to no one who had anything similar happen to them. I'm documenting it here in the event that somebody, someday, might. Cheers and thanks to everyone who offered suggestions. Scott

 

Thanks for posting the solution Scott, much appreciated.

Hope things continue to shift smoothly.

 

I have had this weird problem similar to orignal post.


My car has a problem getting into "D" you have to put it into a lower gear first then you can put it right into D without any problems. I am not a mechanic or anything close to it. At first I thought it was a transmission problem but as soon as you put it in D weather it the car was moving or not it will drive fine. Meaning if I just get to the car and start it up and put it in 3 first then into D --without-- moving the car the car will operate normally.


thanks if anyone can help me with this

 

peruano:
I've come to discover that both the linkages (the physical cables that move when you use the gear selector) and the electronic switches involved with gear selection can and do wear out. If your transmission is smooth all the rest of the time (no excuse, by the way, for not making sure you have good clean fluid in there), I suspect your problem is not with the gearbox. Do you have a trusty independent Jag mechanic nearby? I'd talk to him/her about this. My problem ended up being the Rotary Switch itself - sometime called the PRiNDL switch. I got one used on line and had it installed, and no problems since. It was expensive, though, because replacement required quite a bit of tear down in the dash. You may get lucky - and you very well could - and just need an adjustment rather than replacement. Please let us know what/how it gets remedied!
Cheers,
Scott

 

peruano:
Sorry... I just noticed that you are driving an S-Type. So, I have NO idea if any of what I wrote above applies to your car. Do some digging in the archives to see if it does.
cheers,
Scott