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Discussion Starter · #1 ·
I have a 2012 expedition (6R80 Trans) I’m really lost at this point and would appreciate any input. It started putting me in limp mode and throwing a P0720 code. (Output shaft speed sensor) I drove it like this for a bit and just cleared the code as it came up. The sensor was a part of the lead frame so I pulled it and opened up the valve body to make sure everything looked good. I replaced the lead frame and reinstalled everything. (New gaskets, fluids, and filter as well) afterwards when I shifted out of park it did nothing. Torque converter is spinning but the transmission won’t engage, so my rpm’s are bouncing. I assumed I messed something up while the valve body was apart so I bought a new one and replaced it. I’m still having the same problem. And it’s continuing to throw the P0720 code as well as P0740 occasionally. Do I need to get the TCM programmed? Is there something I’m missing? I didn’t replace the bridge seal (but it wasn’t cracked or broke and went right back in place and I assume that wouldn’t cause this problem.

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One of the possible causes of the P0740 is a low transmission fluid, did you check the level while running? Bit of a pain to do since they did away with the tube.

The TCM shouldn't need to be programmed. You put the transmission back together as it was. If there were mods, then, yes. This is still a 6R80 against the same engine. I've never dove into one of these transmissions, and after looking into it, I will probably keep it that way, God bless you for tackling it. But, like older transmissions, this will only go together one way unless you forced something. Before adding fluid (if it's needed) try wiggling the electrical connection, you may not have had the guillotine clamp fully seated. Also, look for wire damage, From there, I hate to say it, but your probably going to have to go back into the transmission. I did find a fairly good video of a fairly knowledgeable fellow taking on this very problem. It's a little over a half hour and he's about as dry as Ben Stein in Ferrus Bueller's Day Off, but I did see a few others that I wouldn't trust as I really didn't like their procedures. Please also see the possible causes for the codes, you may have noticed something or may notice going back in.

P0720 code possible causes
  • Faulty Output Speed Sensor (OSS)
  • Output Speed Sensor harness is open or shorted
  • Output Speed Sensor circuit poor electrical connection
  • Faulty Powertrain Control Module (PCM)

P0740 code possible causes
  • Low transmission fluid level
  • Dirty transmission fluid
  • Faulty torque converter clutch solenoid valve
  • Torque converter clutch solenoid valve harness is open or shorted
  • Torque converter clutch solenoid valve circuit poor electrical connection
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