Hey guys, I was having some issues with my transmission. I have a 2004 f-350 6.0 with a automatic transmission. My original transmission went bad so I got this one and it’s from a 2005 f-450 I used all my sensors and wiring from my old tranny.I got it put in, it reversed good and I started to drive forward and got maybe 50 yards and the tow haul light started blinking, it idled just under 1000 RMPS and has a hard time shifting. I ran codes and I got a p0720 output speed sensor insufficient input. I thought it was the sensor so I replaced it and the same thing happens, is there anything that changed like maybe it’s not the correct sensor? Does my truck need to be reflashed so it will talk? Any help would be great, thank you

 

The issue is probably in the connector or the wiring since it gives you that code with both sensors.

 

@bismic i looked at the connector and as much of the wiring I could without messing with the entire loome and didn’t see anything wrong. Could it need reflashed so it will talk or do you not have to do that when installing a new tranny? Or is it just a wiring issue, I’m not sure where to start taking things apart at

 

I am not aware of needing any re-flash to establish communication.

I hear you on not seeing any wiring issues, but unfortunately it could be anywhere in the harness. You might considering installing a new wire (make it a parallel wire temporarily) from the sensor to the PCM. This wire will connect to the RIGHT connector of the PCM (C1381b) - ie closest to the radiator. In my 2006, it is pin #28 of C1381b (dark blue wire with a yellow stripe).

Or better still - do a resistance test on the wire (from PCM to the sensor)!

 

@bismic I wasn’t aware of any re-flashing needed either, but I don’t know that much about transmission, I just wanted to check with someone that knows a little more. OK I will do a resistance test and see if I can figure something out there should be little to none resistance correct?

I took it for a drive just to see what it would do, if I shut the truck off and turn it back on the light goes off and it drives like normal until I shift into second gear, then it starts idling funny and the light starts blinking and everything. I shut it off and restart it and it does just fine going in first gear. Is that just the system resetting and not having an issue until it Has to think of what to do and then find that error?

 

Definitely should be less than 2 ohms. I would think closer to .5 ohms.

Not sure why the erratic shifting other than the speed sensor value being flaky.

 

Okay I will try and find some long enough leads to test it all, I need to test all 3 wires that leave the connection right? Or just the one you said about?

im not sure either why it only does it when it goes into second for the first time and when I shut it off it resets maybe

 

The Pink wire with White stripe is the buffered 12V power to the sensor. Even though it is 12V, it is still called a reference voltage. It ties to Pin #1 of C1381b. quite frankly if there were to be an issue with this wire, you would probably have other problems/codes.

The Black Wire with White stripe is called the signal return, but it is functionally a ground. It also shares other circuits. It connects to pin #22 in C1381b. Again, it would probably cause other codes if it had an issue.

The circuits shared as mentioned above, are sharing with the Transmission Range sensor and the speed sensor assembly (turbine shaft speed and Intermediate shaft speed).

No harm done in testing them all though.

Couldn't answer your "why" question. I am only following the code, and proposing some basic checks because of the code.

 

Okay I’ll try and make sure all of the wires are good, if I where to run a separate wire I would just cut the dark blue wire at the pcm and connect a separate wire to the sensor and that should be all?
it’s okay I really appreciate all the help your giving me

 

If it is bad in the resistance test, cutting the wire and adding a new/separate wire is probably the easiest way to go. Some people replace the harness, but that seems extravagant to me. Finding the problem is the best thing since it may be rubbing against something and other wires may be "at risk". That may not be easy to do though.

Adding the temporary wire is probably a "last resort". I hate cutting wires unless I truly know the circuit is bad.

Let us know the results of the resistance test before cutting wires.

 

Yeah I get that, I’ll test them right now and see what I can come up with and let you know. Thank you

 

@bismic i may be doing something completely wrong here. But I tested all of them and my meter reads OL on every single one. I touch me leads together and it reads 0.00 but when I try and touch the wires using paper clips to make sure I have good connection and everything it reads OL

 

Doesn't 0.L mean an open circuit?

 

Yes I believe so. “Open Loop” ol

 

I would get some backprobe pins so you can insert them from the back of the connector. They work well and do not create an opening for moisture.