LR4 gearbox fault
 

Hello there, first time poster, here is a doozie.

I bought a 2010 LR4 several years ago, and for the most part the car had been perfect... until now. :) - I'm hoping someone can shed some light on this mystery...

2010 LR4 with 132,000 miles (ZF 6HP28 6 speed automatic), 5.0L petrol US model - always serviced.

Symptoms:

When cold (or transmission temperature below 150-170, there is no issue, gear shifts without issue).
At transmission operating temperature (>190F) when shifting from D to N (rarely) or when shifting from R to P (everytime) the car will throw a gearbox fault (yellow warning light) and the instrument cluster will NOT display the gear selected (although it will engage the right gear)
Once this condition appears, the car will drive in safe mode (no other warnings in dash), shifting smoothly all throughout. Also, once this warning is present, the selector will not move from Park once it is selected (although since it is not displaying P in the cluster, it will also warn that vehicle is not in Park although it seems to be - havent tried to see if it rolled :) )
This occurs irrespective of incline when parking the car.

By waiting for temperatures to lower, or clearing codes in ECU, the selector is able to move from Park, and the car is back shifting normally (irrespective of temperature - of course it is not a permanent fix, next cycle, error codes come back, symptoms return)
Codes present when this fault occurs:

P0850
P0915

(generic OBDII reader)

Without the fault appearing (that is to say, it reached operating temperature, and I've not shifted away from D) - it has no issues shifting, no shudders, rough shifts, etc.
Battery has not been changed in at least 3 years (voltage shows 12.5v at rest, over 13v when running) - I'll confirm these again.

Took the car to 3 mechanics:

1. couldn't figure out even how to reproduce the issue
2. wanted to replace valve body without checking anything else - bit rich for my blood before any other troubleshooting - didnt bother to check fluids, although noted an oil leak that looked like from transmission pan.
3. worked on a couple of other items (oil leak which contaminated the vacuum pump - replaced + fuel injectors hairline leak Right bank) - looked at the gearbox fault, threw hands up, said new tranny or new valve body - didnt get a sense for real troubleshooting there.

What I am thinking it is and is not related:

1. NOT the brake light switch (brake lights work and car detects brake pedal press and depress correctly without any fault)
2. NOT brake lights (overhead brake light is broken (ran into my garage door - dont start :P )) however, this fault is very recent, all lights are working as expected
3. NOT battery, although perhaps on lower side, charge is consistent, in a couple of weeks or monitoring
4. NOT shifter related, shifter should not be affected by transmission temperatures
5. IS: given temperature relation to symptoms, I suspect a leak + cracked seals in the transmission, next steps would be a tranny service + flush + replace all seals, connector sleeve, etc....

Am I on the right track here? I'm over $2500 already in repairs and diagnostics, and really want to dig to root cause before bitting $5000 on new valve body + wife will either kill me or make me buy a Nissan (same effect...)

Thank you for any help.

Thank you Abran for the kind offer, I'm unfortunately in the Sacramento area where would be unwise to drive over to get that diagnostics.
I'll look into the GAP tool - looks very useful going forward.

I hate to ask further, but I take it from your response, this isn't something "well known" to occurr, etc? my searches on the web do not find an exact match of symptoms either.

Many thanks again!

Thank you for having another look, I think I will either buy the GAP tool or take to the nearest dealer and have them pull codes to get some more information.
In the meantime, I had one of the shops give me the code they saw themselves (which they neglected to give me before hand):

P0850-8F
P0915-01
U0402-00

Are these of better use for now?

Hi Abran,

Many thanks for that. I'll order the GAP tool this week. The car has been great until now, I'd hate to get rid of it so I'll stick with it for a while longer. :)
I'll post back an update once I have the readout.

Hi
Have you any news about? i have a some trouble with my lr4

Thanks, Sergey

LR4 gearbox fault
 

Good day

I am experiencing the same problem with my LR Disco 4, I would like to know if you finally resolved the issue of Gearbox Fault, if so what was the solution? Thank you!