Some of you may recall the shifting issues I’m having. The car refuses to upshift when hot, driving in start/stop traffic, such as stoplight to stoplight. When you get to around 3,000 rpm, it will upshift, but if you slow back down at the next light, you can feel it downshift and you start all over with the issue. When the issue is active, you can cruise along at maybe 45-50 mph, and it isn’t shifting. When you slow down, it does not upshift to let you “coast”. It’s like a Jake brake. It’s stuck in gear, so the engine is helping you slow down as you decelerate.

The tranny was rebuilt due to a loud clunking and banging noise, but it did not fix the shift issue. For my own curiosity, I dropped the valve body to see if I could see any date codes, etc, thinking maybe I was sold a bill of goods and the tranny had not been rebuilt. But I found recent date codes etched onto the valve body and the conductor plate, leading me to believe that those parts were replaced. No date codes on the solenoids, but I did test the resistance, and all were fine, so I assume they were replaced as well. That made me feel better, but it didn’t solve the problem.

Next, I sent the ECM off to G7 Computers to have it rebuilt. It came back yesterday, but did not fix the shifting problem either. They said they found a hardware failure, and I’m following up on that.

Over time I have replaced the brake switch, the transmission module, and a few other parts that I’m forgetting. THERE ARE NO CHECK ENGINE CODES, never have been.

One new item: yesterday when I got the ECM installed, I ran the car to top off the tranny fluid after inspecting the valve body, etc. Very briefly, I saw a “high gearbox temp” amber warning on the dash. When I moved the shifter to another gear, it went away and did not return. Does anyone know what might cause that? I don’t think the temp was actually high because I hadn’t driven it that far, but who knows.

Any suggestions you may have, no matter how absurd, will be greatly appreciated. I am researching topics on the throttle body now, thinking maybe a position sensor is bad or something, but I think I would see a trouble code if that were the case. I’m willing to have the throttle body rebuilt, but I am at my wits end for now.

 

I attach documents that I have on the MB transmission shift problems and relearning procedures that may help you.

 

Thank you for the reply. I am following up on the relay mentioned in the article. I inspected the plug and wiring when I installed the valve body. Everything looked pristine, but I suppose you never know. Do you know where the Jaguar equivalent of the k5 relay would be located? The article is talking about a Mercedes vehicle, but I assume the Jag has a similar relay because it’s the same tranny.

After additional research and a conversation with G7 Computers, I am sending my ECM back to them, along with the TCM. It is possible that the TCM is fried, which is what fried the ECM to start with, or vice versa. They will re-check the ECM in case the TCM fried it again, and will also diagnose the TCM. I am hoping that the TCM is fried, because that might explain why the new ECM and transmission rebuild did not fix the issue.

Onward we go. Thanks again, I’m still interested in the relay mentioned in the article.

Edited to add: I previously believed that I had ruled out the TCM because we swapped it out last fall, but the problem remained. I figured it was nearly impossible that two unrelated TCM’s would exhibit the same problem, so we put mine back in. With what I’ve learned in the last 24 hours, I now believe it is likely that the ECM was fried, and could have fried the TCM. When we swapped TCM’s, the faulty ECM caused the “new” TCM to fry. G7 Computers told me before I sent in the ECM that it was very likely that another component in the system would be defective, but I believed at the time that the TCM was fine, and the rebuilt transmission was no longer defective. I now believe that the tranny is probably fine, but the TCM is probably fried. We’ll see what they find.

 

Here's the 722.6 Service Manual. The fault codes are provided from page 29. Perhaps you should do a scan with a scanner that can read the transmission codes before going into attempts to repair components that may actually not be faulty and the cause of your problem.

As for the relay (I presume you mean K12, not K5), I couldn't find any equivalent in the Jaguar wiring diagrams. The 722.6 TCM gets power supply from the fuse #1 in the Engine Compartment Fuse Box (the larger one).

 

Yes, K12, sorry.

Where would I find a scanner that can read transmission codes? Is it a regular OBD scanner? I have an app for my iPad that I use for the port under the dash. I’m guessing this is much more complex than that. I was not aware that the transmission codes would not show up as a regular trouble code (check engine light). The manual indicates that there are diagnostic ports under the hood that you hook up to read transmission codes. Did I read that right? I didn’t know that, and I am wondering if it takes a special reader.

Next step might be sending it to the crusher! I’m not at all sure that I’m equipped to dig that deeply into the diagnostics. Who could do that? If I was to attempt to measure the resistance on the various pins in the wiring harness, where do I place the other lead? I can put one lead on the pin, but where does the other one go? Probably a dumb question, but I honestly have no idea. I suppose once I figure it out, it wouldn’t be impossible to do the tests.

I generally enjoy figuring stuff out like this, but this deep diagnosis is completely new to me. Thanks for all the information. It is both helpful and intimidating!

 

Ok maybe I’m figuring it out slightly. I can measure the resistance across the pins in the connector that plugs into the TCM. I would put the leads on the two pins indicated in the chart, and read the resistance. That would tell me if there is a short in the wiring, and/or a defective solenoid. Since I just pulled the valve body out and checked the solenoid resistance, I would start with the wiring if the resistance was incorrect. Do you suppose that the connectors are the same for a Jagaur? The manual talks only about Mercedes and Chrysler, but probably would be the same for Jag...?

I still have the question about the diagnostic reader needed to read the transmission fault codes. But I might be able to do some preliminary checking with a multi meter.

 

The right tool would be the jaguar/Land Rover VCM scanner and IDS software but you may have a problem finding a workshop which has it. I don't think Jaguars have any special port for the transmission scan, everything goes through the OBD port under the dash. You can try with a workshop which has a good universal OBD scanner, perhaps check with Mercedes workshops. Otherwise, someone on the forum will probably be able to advise which of the not too expensive "DIY" scanners are good for transmission codes reading. Possibly Icarsoft i930 or Actron CP9575?

 

I’m learning exponentially over the last hour by reading the transmission manual you posted. On page 26, it describes my problem in perfect detail. There was pop spilled on the center console at some point before I got the car. I cleaned it up, but did not replace the TRRS switch. Page 26 discusses this exact issue.

I have figured out how to test all the TCM pins/ports for resistance and/or voltage from the solenoids and temp sensor, and I am working through them all. The solenoids all test out ok. I am now working on the ports for the transmission temperature sensor, but I think I have to turn the key on and put it in drive or reverse to get a reading.

After that, I am going to test voltage from the TRRS switch at the TCM. When I read that on page 26, I couldn’t believe it. It is EXACTLY my problem, right down to the spilled soda.

I have to call it a night for now, but I’m on to something. I don’t know what I’ll find, but at least I might learn where the problem is. I can reinstall the computers with confidence that they won’t short out right away.

Thank you for the WONDERFUL help you’ve given me today! This forum is invaluable. I will report back over the next few days.

 

Well, you did not report the soda spill earlier. In that case, it is quite likely that the only problem is contamination of the selector (sliding) switch. The pictures show my spare switch which I have not opened up yet (for inspection and cleaning) but it seems easy - there are some 4 screws that hold it together.

 

The 722.6 transmission in my X100 has similar symptoms - sometimes after an hour or more of stop-n-go driving in hot weather it starts to upshift at around 3000 rpm. I was not very concerned about it because I purchased this tranny at the junkyard very cheap and knew that I would need to rebuild it sooner or later. But after reading that rebuild didn't solve the shifting issue, this becomes more interesting.

 

That's what I'm thinking now too. I never even considered the spilled pop before reading it on page 26. When I first got the car, I removed the entire interior, replaced the carpet, cleaned, cleaned, cleaned everything, but never once thought about it causing the shifting issue! It was a gooey mess, but I got it all cleaned up......except for this, apparently. Hopefully tonight I will be able to finish testing the voltage and resistance discussed in the manual, and I will tear the shifter apart regardless of the voltage test to see what I can find. If this ends up being the problem I'll owe you a beer!

 

Ok several developments to report. I tested the ports for the shifter module, and they all tested perfect. Since the issue is intermittent, I took that with a grain of salt for now. I removed the shifter unit from the center tunnel. I disassembled it and found it to be grimy and very dirty inside. I opened up the box where the module itself resides, and found it to be a little grimy in there too. Either way, I’m replacing the shifter unit to be safe.

Another issue: I finished up all the resistance tests. Ports 13 and 34 are for the transmission temp sensor. I get no readings. Nothing. No volts, no resistance. So I unplugged the main connector from the tranny, and strung speaker wire down there. I tested for continuity in all the wires, thinking maybe wire 13 or 34 was broken in the harness. All tested perfect continuity.

Not sure where this leaves me yet. The issue with ports 13 and 34 (temp sensor) is either: a bad temp sensor inside the transmission itself, or I’m not doing the test correctly (very possible, more on this later), or it has something to do with the module on the shifter assembly.

As far as doing the test correctly: the book says you have to have it in reverse or drive to conduct the test. I did, but I also have the ECM and TCM completely removed, and I’m not sure where these wires would get voltage right now. So, maybe I’m not doing the test right.

Not sure what the next step is. I’m getting a shifter assembly because the book specifically talked about it being my exact problem. Maybe I install it and then retest wires 13 and 34 again....

Other suggestions are welcome. So far 13&34 are the only issue I’ve found.

 

See the attached documents.

To do the resistance test of the fluid Temp Sensor, you have to put the shifter in R or D. The measurement should be between pins 33 & 34 (not 13 & 34) of the TCM connector and you should get 800-1200 Ohm. For this test, you do not need to have the TCM (or ECM) nor the shifter switch-box connected. Another way of checking the Temp Sensor is directly on the pins of the round connector on the gearbox. Again, you have to position the shifter in R or D and measure between pins 4 and 12 of the connector.

A fairly common failure are the Speed Sensors on the Conductor Plate which would prevent shifting. However, it is not possible to check them with a multimeter; you would need an oscilloscope for this or a good OBD code reader. If you find all other multimeter readings to be good, and once you have cleaned all the contacts inside the shifter switch-box, check the gearbox operation again. If the problem is still there, you will probably have to replace the whole Conductor Plate as the Speed Sensors cannot be replaced separately.

The Conductor Plate should actually have been replaced with a new one during the gearbox rebuild as it is a somewhat weak point on these gearboxes. The etched fresh date on the Conductor Plate probably just means the date when it was removed/reinstalled. You should look for the year of its manufacture which is shown in the casting of the plastic body, on each side, in two small round chops with an arrow inside. The arrow points at the year on one and at the month on the other chop.

If you decide to buy a new Conductor Plate, you can get it much cheaper if you search for it as an MB part for 722.6 (easily available on Ebay).

 

Interesting. The manuals you posted the other day say pins 13 and 34 for the temp sensor (page 23). I will test 33 and 34, however, based on this new information. Looking at the circuit diagram you just posted, compared to the manual you posted previously, it appears that the only difference in the pins being tested is 33 and 34, vs 13 and 34.

Yes, the conductor plate has the small round chops, as you called them. I used the word “etched” but it was definitely the little raised round things with the arrows pointing at the date. So I am confident that I have a new conductor plate. I’m not saying the issue is not related to the speed sensors, but if it is the speed sensors, it will have been two bad conductor plates in a row with exactly the same problem. Not impossible, but probably not likely. I am leaning toward the shift module because that’s never been replaced during any of my testing/troubleshooting over time. I will use pins 33 and 34 for the temp sensor test, and report back when I can.

Thanks for your continued follow up. I feel like I’m making progress!

 

Here are a few pictures of the shift assembly and sliding switch after I took it apart. A lot of dog hair or something in there.

 

Is that some grease or soda residue along the switch tracks on the PC board? Anyway, give it a good clean-up.

 

I’m not sure what it is but I’m pretty sure it shouldn’t be there.

By way of a progress report, I clicked the shifter cable into drive and tested resistance across 33 and 34. I got 990 ohms. I think I feel good about that. I’m going to close the book on my resistance testing project for now and focus on the shifter module. I’ve ordered a replacement unit. If it’s soda or other residue in my old one, no telling what damage it caused. I don’t want to put the old one back in, even if I clean it up.

The new unit won’t arrive until next week. In the meantime I will reinstall the ECM and TCM this weekend and get that buttoned back up. If the shifter module doesn’t fix it, it’s off to the crusher! Haha.

 

While waiting for parts, I dug deeper into the shifter assembly out of curiosity. How does the car know when you move the lever from D to 4? I see how the lever disengages from the stop of the linear switch, and engages with the bottom slider, but I cannot find a microswitch or anything that would tell it that the lever moved from D to 4. Once you move the lever forward into 3 and 2, obviously it slides the contacts along the linear switch, so I can see that. But that very first move, from D to 4, any idea how the car knows you did that? It doesn't appear that, other than physically moving the lever, there is anything mechanical or electrical that would tell the car you moved the lever. Once you shift from 4 to 3, then yes, obviously it moves the slider. But from D to 4.....hmmmm....? I'm not seeing it.

Not that it matters, but I would like to know.