I mentioned it in post #17.

 

Well now that I am measuring it right, the resistance readings have come out just fine.

A4wd: 61.7 - 68.1 ohms - reads 65
4HI: 656 - 670 ohms - reads 665
2HI: 1.50k - 1.53k ohms - reads 1521
4LO: 2.32k - 2.37k ohms - reads 2.3k
Neutral: 1015 - 1035 ohms - reads 1029

this means the switch is okay and the new suspect is the TCCM right? Where else would the erroneous voltage come from if the resistance in the switch is fine?

 

Right now I'm wondering about a problem with the motor lock circuit. With no voltage applied it is locked, preventing the motor from changing range/modes. Did you check that 20A ATC fuse in the underhood fuse block? Check it visually, but also check it with a test light/volt meter connected to B(-) by touching the metal tabs on the backside of the fuse. Should be HOT AT ALL TIMES, but I'd also check it KOEO.

Then with everything connected back up, I'd backprobe the pins using T-pins on C1 on encoder motor, KOEO, for B(+) (red test lead backprobed on pin C (ORG wire) and LOC SOL CONTROL/OUT (black lead backprobed on pin D (TAN wire). Should read 0.0V. If your test leads aren't long enough for you to watch in cab, have someone place trans in neutral, foot on brake and one at a time push each button on selector switch, giving time between each press. If LOC SOL control signal circuit is working correctly, you may see some voltage fluctuation as encoder motor shifts, then drop back down to 0.0V (except A4WD position where voltage would remain).

That test should confirm whether or not motor lock circuit integreity all the way thru the system. Motor lock could be ruled in/out.

 

Okay so I checked the 20a ATC fuse - the fuse itself is fine, reads 12v at all times.

At first I misread the "backprobe" part and disconnected the plug, only to realize my mistake when the 4x4 selector switch was disabled. When I plugged it back in and turned the key on I heard some humming and intermittent clicking from the encoder motor and the TCCM. I can't tell if the clicking I'm hearing is the encoder motor brake engaging and disengaging, or the motor trying to turn against the brake.

I then backprobed the plug properly while it was plugged in, but got no voltage readings with engine on or off in neutral and patiently pressing the various 4x4 buttons. Did not see any voltage on 4auto.

I can unplug the encoder motor again and get a recording of the various sounds if that would help identifying exactly what's happening.

 

So I've been thinking. When I pulled off the actuator cable, I didn't attempt to pull the shift fork manually from where the cable connects. The cable itself moves fine within its sleeve, but I couldn't get it to budge when it was connected.

I've failed to mention that while the selector switch shows im stuck in 4 low - the light only flashes and the front wheels are not rotating despite the front driveshaft spinning. So the front axel isnt engaging. My scan tool had the two lines that read "front axel req : yes" and "front axle switch: unlocked". Atleast I know the sensor is working?

tomorrow I'll remove the cable again and try pulling the fork directly. If I can't get the front axle to lock while in neutral with 4low flashing, somethings up in the front diff. Even if that is the case though, I don't understand why I can't get back to 2 hi.. both the propspeed sensors read, the engagement sensor reads.... and none of this explains the erroneous voltages at the selector switch... GAH this thing drives me nuts!

Also due to pick up that spare TCCM soon and swap it in. God that'd be nice if that solved the problem...

Edit: I just read someplace that if the Neutral safety switch isn't mounted perfectly it'll cause issues for the TCCM. Before getting stuck in 4low, I replaced the NSS after breaking it trying to remove the glued connector - I broke the plastic retainer on that clip, but I just glued it into to the new NSS. I used a zip-tie to keep it in place while the glue dried, and I felt I had it seated 100%... how can I verify communication between the NSS and the TCCM?

 

The fact you aren't seeing the voltage for the motor lock come up at all, has me thinking the clicking you're hearing is the motor fighting against the lock...plus what your scanner stated. A capable bi-directional scan tool would allow you energize the motor lock circuit (thereby unlocking the motor) and should allow you to shift the transfer case (or not if it is bad). Fairly certain the motor lock is just a full OFF/ON type of signal and not a PWM. So the control module is just suppling the ground (TAN wire) to energize the motor lock.

Not sure if you've done it yet, but verify you are getting B(+) voltage on pin C (ORG wire) where you back pinned at the encoder motor. This time just connect black lead to known good ground, red lead to the back pin. You should see B(+) at all times without pushing anything. This will verify no open in the wire all the way from the fuse.

Then try moving to the other end of the TAN wire (at the control module behind the kick panel). Back pin the LOC SOL OUT (C1 pin E1 (TAN wire)), black lead on that back pin, red lead to B(+) post, KOEO, trans in neutral, foot on brake, try selector switch buttons, watch for voltages.

Do you have an incandescent test light?

I know you stated you had disconnected the TCCM connector to take a look for any apparent issues. Just so I'm clear, and we're using the same nomenclature, did you also disconnect the connector at the TCSCM (module behind the kick panel), or is that what you meant? Just so I know whether you disconnected it or not.

NOTE (again, just in case): If you do get another encoder motor DO NOT test it without it being installed (i.e. supplying 12v to see if it works). You'll probably damage it.

 

Oh ive already installed a new one, had the old one off anyway and it looked suspicious.. that's when I verified I could rotate the transfercase shift shaft into its 3 indents. The new encoder installation guide explicitly stated to install it in 2hi - I wasn't certain which position on the shaft was 2hi, but I just rotated the shaft to match the new encoder motor and called it a day. When I then fired up the truck, the red neutral light came on momentarily - then some more humming + clicking and it went back to flashing 4 low.


My apologies for not communicating that previously, i feel thats a major detail I've left out 😅

I'm picking up that 2nd TCSCM tomorrow morning, ill play that swap, and then if thats not it, ill continue on with the orginal part and your diagnostics.

Btw Ive gotta give you thanks for so consistently replying to the thread. I've been real stuck on this and you've been a phenomenal help.

 

No apologies necessary, just wanted to make sure we're talking about the same components. I've seen (and been guilty of myself plenty) where someone may be talking about the encoder motor and thinking TCCM=Transfer Case Contoller Motor, or talking about the control module thinking as TCCM=Tranfer Case Control Module.

 

Confirmed voltage at all times on the orange wire at the C connector.

"red lead to B(+) post" I'm confused as to what you mean by this. I'm assuming you mean to ground the red lead, I did so on the little frame that the module mounts to.

So having back pinned the Tan E1, KOEO, with trans in neutral, foot on brake, trying the selector switch buttons and watching for voltages - I got 12v steady with no variation.

The TCSCM i picked up was the wrong model and gear ratio so I never gave it a go - I'll have to swap it for another one tomorrow.

so to my understanding, either I probed it wrong or he TCSCM isn't sending the unlock signal. There's a list of things the computer checks before sending that signal right? I tried digging for that info in my pile of links but I didn't have much luck.

 

Still waiting on that replacement TCSM. Removed the actuator cable from the front diff, went and manually pulled on the shift fork and successfully engaged the axel. There was plenty of strength left in the retention spring, no clicking or anything unusual. However actually pulling the fork myself definitely revealed that my actuator was not pulling the cable far enough.

But regardless - I'm going to see if I can find the ohms and/or operating volts for that sensor on the actuator cable housing - that's the sensor that confirms the position of the axel engagement gear right? That would explain the TCSCM refusing to send the unlock signal to the encoder motor brake.