Transmission Issue related to P0713
 

Ok, folks, short term lurker, finally became a member today.
I have a heavy automotive hobby and the facilities at my residence to do pretty much any mechanical or electrical repair, plus limited body and glass repair. I don't paint as a spray gun is just a weapon in my hand.

The preliminary stuff:
I bought a 2005 X5 3.0 Auto transmission down in Maryland that ran fine, but did absolutely nothing when placed in any position on the shifter. No movement, no noises. Vehicle has a really nice body for 167,000 miles. Instead of buying a used tranny for it, I picked up a rollover in Cleveland with identical model year and powertrain; 120,000 miles. It lot "moved" when put in gear, but could not really drive it due to broken control arm and strut at LF wheel. It only had the 4x4 rollover mitigation light illuminated, which my have been from an extended period with a dead or disconnected battery. It did not have a MIL light on or "Trans Failsafe Prog" warning.
Rather than just swap transmissions, I dropped out the cradle and swapped the complete lower mileage powertrain and put the rollover engine/trans/transfer case in the good body, with the exception of the front suspension. I actually split the oil pan off the bottom of the engines and mated the original front suspension/knuckles/rack to the new power train, avoiding disassembling the axles and front final drive through the oil pan. (That was fun while the engine and powertrain were hanging on my shop crane!!) I did bring the rollover transmission control module along and used it in the new body, keeping matched TCM and transmission together. Put it all back together, and what do you know, it fires right up.

The issue:
I had no codes until the engine temp gauge stabilized mid-sweep, and I assume its at operating temperature.. At that point, I got a "trans failsafe warning" followed by the 4x4 rollover mitigation light and then an illuminated MIL. The transmission had the forced downshifts as I slowed down to a stop.
Came home and pulled the code P0713 "Trans fluid temp sensor A circuit high input"

Did some searching here on the forum and found that replacing the harness inside the transmission case, which apparently carries the fluid temp sensor, might take care of that. Bought the new harness. Dropped my fluid, put in my new harness into each solenoid and changed the filter while I was in there (trans pan was clean with only a slight bit of material stuck to the magnet). Replaced the fluid. (Data scans during this time always showed a -40 degree fluid temp, like it is not seeing any signal.)

Took it out on the road again and when it reached operating temperature it again triggered all three warnings, including another P0713 MIL. I then changed out the complete external transmission wiring harness from the transmission case up to the oxygen sensors and over to the cowl bulkhead disconnects. Got in and drove about 55 miles/90 minutes with no warnings. I was happy as a clam thinking I had the issue nailed, when all of a sudden I start to slow at a stop light and feel the hard downshifts as I came to a stop, with the "trans failsafe prog" warning, the 4x4 rollover mitigation light on, and an illuminated MIL. Scanned it again and got the same P0713 code. Before that, it shifted very nicely, and the vehicle runs well otherwise. It has not thrown any other codes since I put it back together. I did also swap the temperature sensor in the cowl bulkhead disconnect "box" that is integral with the external transmission harness.

Anyone have any thoughts about where I might look next?

(Forgive me if I have yet learned all the BMW acronyms for certain components--I'll get there. )
I appreciate any insights anyone might be able to share.

I can't help you, but I will follow this. Sounds like you covered all the bases to avoid having to "code" any modules. THere is something that is getting overlooked. These things can be so temperamental. Over engineered.

To add more detail, I did inspect EVERY pin and connector as I disassembled the harness and TCM. Everything was clean and shiny, with no bent or distorted pins.

maybe the cars were identical, but one had a revision. Are they the same production month and year? Maybe trace out the pins for the temp sensor, all the way to the TCM.

Thanks for the replies, Cape X5 and Slick GT1. I will have to check production dates to see if there has been any revision. I may have to ring out the individual wires from the TCM to the temp sensor. I thought I had that by changing out the entire harness. The perplexing thing is the delay in the fault code returning after driving for that time/distance after swapping the entire harness. I ran normally for quite a while before reverting to the failed state, with same code.
I won't let this thing beat me!

A member here (RRPhil) makes a living fixing automatic transmissions.

He hasnt been here in a while, I think he is in the Range Rover forums usually.

He has postings here with technical info that may help, do a search for them.

Or maybe track him down in the UK Range Rover forums.

He looks to be very knowledgeable on these transmisions and hopefully he can help you.

I will try and contact him. Thanks.

No problem. Good luck!

I would get an infared thermometer to measure the temp at the trans pan. Or if you have inpa or any BMW specific software look at the trans temp sensor and see how hot the fluid is getting. Could be that the fluid is getting hot.

That's like changing the ect sensor because the engine is overheating. The engine is probably over heating but I would look into why it is over heating before changing the ECT sensor.

The lines from the trans cooler might be plugged or the trans cooler itself might be plugged. If there's a thermostat, the thermostat might not be opening when the fluid is hot. Don't buy cheap garbage thermostat, buy a genuine BMW part.

Thermostat. Expansion tank, automatic transmission made by BMW. #17111437362

Lots to check for before replacing parts.

I think RRPhill is more knowledgeable in the ZF trans and not the GM trans found in the 3.0 X5.

There's a trans rebuilder Gary Ferraro that post a lot of video on Youtube. Perhaps he can help the op out.

https://www.youtube.com/channel/UCWa...yLyQ7zjW9LF-xg

Good Luck and post back what the problem was if you find out.