Fan Speed error code and Intermittent 2nd gear starts

[BWGuy]

OK. I've searched high and low, but I've not found anything definitive on this issue, so I'm putting it out there to the braintrust.

My nephew picked up an 03 TB 4wd a few months back, and about 3 weeks ago he came to me with no 3rd or 4th gear.
Inspection up in the pan revealed a LOT of clutch material, and after the fresh filter and fluid and PCS (longshot) he still had no 3rd or 4th, so I took the tranny out for a rebuild.

Now it's all back together and in, and for the most part it's shifting well and firmly through all gears and locking up the TCC and such, BUT...
sometimes it just drops out of 4th down to 2nd and then wants to start off in 2nd and stay in 2nd unless I pull into manual 1st.

I have a PC and software that lets me monitor shift solenoid status and such, and according to the data, the PCM is commanding Shift Solenoid B "ON" and Shift Solenoid A "OFF" all the time unless I pull into manual 1st, at which point both solenoids come "ON" and I get 1st gear.

This is pretty random so far. The truck seems A-OK, and then this happens, and then I might shut off for a minute and it's back to good again.

Right now, the only trouble code is for the cooling fan speed sensor, so I'm going to swap out the clutch module with the one from my truck this afternoon to see if that eliminates the trouble code, and if it does then if it also eliminates the transmission issue.

Does this sound familiar to any of you guys? Or gals?

[Trail X]

Solenoid A Off and Solenoid B On is commanding 2nd gear. Both A and B on is 1st gear. A and B off is 3rd. A on, B off is 4th. Reference: http://jd.offroadtb.com/trans-docs/4L60 ... ic-key.pdf

So it seems like a sensor/computer issue to me, not a hardware issue internal to the transmission.

For your reference, you can see the differences that should be present between overdrive-range 1st gear and the manually selected 1st gear option by going through that file and tracing the transmission schematics at the same time, they are meant to go together:
http://jd.offroadtb.com/trans-docs/4L60 ... matics.pdf

Hope that at least gives you some fodder for your investigation. I am not familiar with that particular problem that you report.

[BWGuy]

UPDATE: ISSUE RESOLVED!!!

Turns out it was the pressure switch manifold (TFP). I'm not sure we won't need a new one at some point soon, but using the software that lets me monitor stuff, I noted that the TFP was signaling D2 all the time unless the shifter was pulled into D1 or Reverse. The NRP pins are all open in D2, but in D1 and Reverse the N1 pin is grounded. So that means the R and P pins were staying open circuit in shifter ranges that should have had them grounded.

Blah blah blah, I took the switch pack out, cleaned it off, poked the diaphragms a few times manually and checked that the pins were grounding and opening as they should, put it back in, and voila... everything works great.

The switch pack looks like it should be pretty well sealed, but with all the metal fines that were in the transmission from when the old 3/4 clutch gave up, it may be that it was clogged or stuck open/shut or something. Dunno... like I said, might be buying a new one soon anyway. But at least I finally put a drainplug in the oil pan so dropping the pan is no drama anymore.

Nephew is happy for now.

[BWGuy]

BTW... the fan speed sensor circuit is still bad, and swapping the known good clutch from my TB to my nephew's didn't help, but at least we're outta the woods on the tranny issue.