My LR3 nearly stranded itself yesterday.



Got a dash fault when driving on a gravel road yesterday, “Transmission Fault - Limited Gears Available”. I stopped the car to run diagnostics with GAP IID tool, and 4 modules repeated the same code and would not clear: “Lost communication with Transmission Control Module - Bus signal/message failure - missing a message”. Modules were Parking Brake, Suspension, Terrain Response, Transfer Case. With these codes present, the car would not start and shift lever would not leave P.



After some fuss (giggling shifter, cycling ignition between Pos I/II/III, and attempting to clear codes), I was able to clear the codes and start the car. We made it 100 yards before the codes returned. At the next stop, I was unable to restart the vehicle again and did the following:



Reseating mechatronix/transmission control module loom* —no change.

New brake light switch — no change.



4x4 Info screen showed vehicle in Neutral when it was in Park. Inspecting the shift linkage*, I found it was not loose or binding. Using the shift linkage bypass to put the vehicle into Neutral allowed the shifter to begin working again, and I was able to start the car and drive normally, with no dash lights.



I drove the vehicle 15 miles out on forest road, another 60 miles on the highway, and cycled the ignition 5-6 times as we stopped along the way. No issues. The vehicle drove beautifully on the way home and shifted wonderfully on the interstate, even in stop and go traffic.



*4 weeks/1000 miles ago I did a full transmission service. New filter, fluid, and valve body seals (requires dropping the valve body/transmission control module). I reused the old mechatronix sleeve because the new one would not fully seat. Removal of the transmission heat shield frame requires removal of the shift linkage.



Was this a fluke, or should I be looking into replacement of something? Is there a gear position sensor? Adjusting the shifter linkage? It seems odd that my linkage calibration could be out and only cause a problem now.



Obviously goes without saying this is relegated to city driving until I confirm this won’t be an issue again.

Thank you in advance for any thoughts!

 

Every transmission fault I have ever had was because the BATTERY WAS LOW. From looking at the top left corner, the voltage is 12.3 volts, and should really be 13.2 volts with the engine turned off, and over 14 volts with the engine running. Depending on your battery's age, it might be time to replace it. You might also have some paracytic drain when the engine is turned off, resulting in your battery draining.

 

13.2 with engine off? Nah... 12.5 is considered fine. 13.2 is min operating.

 

I’ve found the voltage reported by the GAP tool is .3v or more low. Resting battery voltage read 12.4v on my multimeter after about an hour of running diagnostics (I.e. ECU draining it). Battery was replaced last December, and the engine cranked right over after we bypassed the shift lever. I’m fairly confident the battery and charging system are innocent on this one 😁

I’m suspecting High Speed CAN bus issues right now. All the modules loosing signal with the TCM communicate through that, and the alternatives are much worse. Alternatives being the gear position switch internal to the transmission, which besides being a PITA to replace I think requires a new mechatronix and perhaps valve body.

Could anyone help me locate splice SJ721/SJ720 and connector C2365 or C2366? This is the path that the bus wires run through from the TCM (the transmission mechatronix connector) back to the bus network. See photo.




I’m also open to other thoughts on the fault source.

 

"4x4 Info screen showed vehicle in Neutral when it was in Park"
Could the shift lever assembly be sending conflicting gear status compared to the actual selected gear in the transmission?

Does this help? Looks like the connector is behind the battery. I don't know how to find splices on my diagrams, or my diagrams don't have them.

 

That’s a big help. IIRC that area is notorious for water intrusion, so it seems plausible there could be a problem at that connector.

I agree with you that the shifter or linkage is another very real possibility. It seems that the lever/bushing on the transmission is common as well, though with slightly different symptoms (namely, no faults). https://www.roverparts.com/transmiss.../TRANSLINKIT1/

Unfortunately, I’m not sure how to definitively test any of these parts to confirm they are the cause. I’ll probably visually inspect all the wiring I can, and if not discovering a problem, it may be an instance where I replace parts wholesale. I’m not a fan of throwing parts at problems, but these intermittent faults are a pain to track.

For anyone following, here is another possible wiring issue I intend to check:

https://static.nhtsa.gov/odi/tsbs/20...04800-9999.pdf

 

Per the TSB in my previous post I checked the connector at the rear left of the vehicle (requires removing the spare tire). This had no chaffing.

I checked connector 2365/2366 under the battery. This area was dry as a bone. I did find some wires which were pulled tight against a metal hanger in this spot. They weren’t chaffed at all, but probably would have eventually, so that was at least worthwhile.

I confirmed the vehicle started in neutral as well as park, so it appears that the shift linkage calibration is OK. Test drive showed no faults. Only fault I got was a nuisance fault for the Parking Control Module, which runs on a separate bus network (medium speed) versus the high speed CAN that the drivetrain uses.

I am convinced at this point that the TCM plug wiggled loose on the few miles of gravel road, and it was stuck in park because the gear selector and position switch were out of sync due to lack of communication. Bypassing the shift lever and starting the car allowed the TCM to start talking to the network again, and all was right with the world.

 

With the gear indicator if you've had any liquid spillage or sunroof leak the pcb on the side of the shifter corrodes and causes a shifter position/dash gear position indication mismatch.

 

Well it happened again. This time on the interstate. Same faults as before, all Lost Comms with Transmission Control Module. Happened on a smooth road at 65 mph so the loose plug seems less likely. At this point it’s also done 200 miles since the last failure. Also seems that the gear selector is OK because it was reporting the proper position on 4x4 screen when it went into limp mode.

Codes wouldn’t clear with car on or off. Car would not start with codes present. No live data from the transmission with codes present (See below).

Disconnected the battery for 10 minutes and car started. Once car started, I cleared the codes and could resume my drive. Made it 3 miles before faults again. This time I was driving with the GAP tool running, watching the live data. All streams were showing “OK” and then switched to “N/A” when fault tripped.

No shop availability at multiple shops until December, so I’m going to have to continue working on this myself.

Ideas are TCCM is failing, tccm connector is bad, bad wiring in the HS CAN network, bad plug elsewhere. Any thoughts on diagnostics to narrow my search?

 

Dang, I was hoping you had this fixed!

Just reaching a bit here...

From the book for U0101-87, the TCM ground could be the culprit, and it is easy enough to check in the left A pillar.