Thank you all for the replies and suggestions! Replaced the front bank o2 sensors and was able to clear those codes. Waiting on the thermostat to be delivered tomorrow and another “fun filled” weekend under the hood! My hope is that this can be resolved without a tranny rebuild and plan to post a spreadsheet of parts, where they were purchased and price to hopefully pay it forward for others with similar issues. Will update with my progress after the weekend and look forward to her running as she should so I can move on to the FUN of upgrades rather than repairs!

Update. Changed the front bank O2 sensors and MAP thermostat and cleared those codes. While replacing the MAP noticed some fluid pooled on top of the hydraulic brake pump and when I opened the cap exposing the wire harness is was soaked with fluid! So began to dismantle the pump and undo any harness tape that was not original. Upon doing so (can’t remember if I’ve mentioned the PO installed an after market stereo) found one wire that was frayed, one with a broken connector and one missing the ground wire. These repairs have seemed to clear up many of the electrical issues (brake lights, PDC, check engine) however still no luck with the transmission fail safe....although it took a bit longer to go into that mode today.

Does your 5HP24 transmission failsafe to 4th gear or to 5th gear? This is significant.
Does the transmission shift through all the gears perfectly when cold and then engage failsafe after 15-20 mins, once the fluid has heated up?
Does the transmission operation revert back to normal again once the fluid has cooled down?

Phil

Does your 5HP24 transmission failsafe to 4th gear or to 5th gear? This is significant. Failsafe kicks it into 4th then 5th gear.
Does the transmission shift through all the gears perfectly when cold and then engage failsafe after 15-20 mins, once the fluid has heated up? Yes! Once fluid hits about 73C failsafe will kick in on deceleration.
Does the transmission operation revert back to normal again once the fluid has cooled down? Once the vehicle is completely cold can shift through all gears. It restarted before completely cold and fluid above 70C will not shift properly and go into failsafe.

Hey RRPhil
 

Would this be your advice for me as well? If so what are your recommendations on parts and other potential issues that should be rebuilt/replaced if I’m going to tear down the transmission? Keep in mind this is my daily driver and am hoping this is something that can be completed in a weekend. Appreciate the replies as I understand you are the transmission guru!

Just put a little more thought into it and could you possibly give me 2-3 options?

Option 1: The quick, easy, budget friendly fix....this is my favorite! :)
Option 2: Not so quick and easy, however while you’re there you might as well.......
Option 3: If it were me (aka the guru as previously stated) I would.......

Again appreciate any and all responses from the forum as well! This has truly been a resource thus far!

Apologize to all in advance for my noob...OCD postings just hoping to resolve the transmission issues. Failed to mention that I have a 2004 Range Rover at my disposal that I purchased at the same time as my X5 (not knowing at the time which vehicle I would be going with). The engine on the rover is locked up however my understanding is that it has the same transmission as my 02 X5? If this is the case (and hoping that the transmission is in good condition) could I use the parts from said rover??

I'm having the same issue and I bought a rebuilt revmax solenoid valve body and I will report on the results.

Transmission Fail Safe Mode
 

I've seen a number of very successful results on xo swapping the valve body with a rebuilt. Much less work than swapping the whole transmission


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