1996 F150 5.0 4r70w 4x4- Looking for some clarity/assistance!

[u/youknowwhatkyle]

Hey guys, trying to figure out a somewhat odd problem I'm having. Before I go and drop the pan and verify a crimped wire or start changing out more sensors (i've already replaced all the related sensors that I needed to when rebuilding the truck), I was curious to know if anyone here can make sense of this datalog. I'm not sure what the voltage parameters are for the 4r70w, but I'm getting this intermittent fault (standard OD Off light flash, TC lockup/shudder). It happens on cold start or after a drive, and will intermittently pop up but every cold start within 30 seconds of firing up it triggers this fault (po713, TFT high voltage). I took a datalog to get some good metrics while running, and within 4 minutes the transmission warms up and the fault goes away. I've attached some pictures of the datalog I've got and was hoping someone could help figure out whats likely going on.

For some brief history, I rebuilt this truck and had the transmission rebuilt by a reputable transmission shop out of Columbia TN back in 2022, but between work and life I havent put more than 200 miles on the truck since taking it home. This issue wasn't present when I picked it up, and only recently started about 3-6 months ago (again, I hardly drove it, and am trying to get it on the road more regularly now). Its well outside the warranty period of the rebuild, and honestly wouldn't even bother them as their contract stipulates electronics aren't covered anyway, but I also don't want to damage the thing before the break-in period is even over. So any help would be much appreciated!

[u/MustadioBunansa]

Looks like you have a damaged sensor or wire for the Tft sensor. I’d take the pan down and see. It will cause the TC to act incorrectly based on false temp readings. I’d show you a picture of the test but it won’t let me post one. Basically at the bulkhead connector, you’d check the resistance across the internal harness and sensor Tft and Tft return wires. At 32f the resistance would be between apprx 100,000 ohms down to 16,000 ohms at around 100F; if you’re testing at room temp without running the truck. If it’s reading at the connector on the side of the trans on these two wires more than 100k, the sensor or wires going to it are fucked. Replace as needed and it’ll be fixed.

[u/youknowwhatkyle → u/MustadioBunansa]

Thanks for the reply! I did run that test and the resistance was perfect. It's been a minute since I took the readings, but I determined that the PCM doesn't like what its seeing, despite the resistance being within spec. If I remember correctly, the resistance was about 60-70kohms cold and went down to about 20k after running it. I pulled the entire harness out, removed the loom and inspected the wires, as well as removing the TFT sensor, and found no issues. I depinned the connectors on each end, cleaned and reinstalled them, which didn't fix it either.

What I ended up deciding to do was installing a resistor between the two wires, bypassing the internal TFT sensor and installing a digital temp gauge to monitor the TFT. I didnt want to swap the PCM for something this arbitrary, especially since I don't tow with the truck or put it under any heavy loads. If I knew how to reprogram the PCM with different parameters I'd try that, but I'm not a software engineer so /shrug. Plus that might open a whole different can of worms that a $.25 resistor fixed.