Nope, I meant to put red lead on B(+) post. The TCSCM supplies the ground that energizes the motor lock (unlocks it). Basically it's an internal switch (ex: transistor) to the TCSCM. By having red lead on B(+) post and black lead on LOC SOL CONTROL (TAN wire, TCSCM C1 pin E1) you should initially see 0V in 4LO. Once the ground is commanded "on" based off of selector switch input I would expect to see ~12V in A4WD. This would indicate that the TCSCM itself seems to do what it should to energize the motor lock (supply the ground).

Since you stated you didn't see any any voltage change down on the encoder motor connector itself...but you were seeing 12V on the ORG wire at the encoder motor connector when meter connected to known good ground...I wanted to see if your TCSCM is supplying the ground at C1, pin E1 (TAN wire) or not.

 

Here is a visual to what I am referring to with my fine Picasso like artwork.

Notice in top image the internal switch to the TCSCM is open, not supplying a ground, not energizing the motor lock (not allowing a t-case shift). This is how it lands in all modes except A4WD. KOEO.

Bottom image has the switch closed, completing the circuit.

NOTE: Unlike what we were doing before at selector switch when you were holding a button to measure resistance. In this case you are just selecting with a normal button push like you would do if everything was fine.

 

If we are both referring to the connector on the front axle (4WD INDICATOR SWITCH), if you (backprobing again) at the switch connector place your red meter lead on a T-pin at the BRN wire (pin A), black meter lead on BLK/WHT wire (pin B), KOER (Key On Engine Running):

-If you see 0V properly functioning switch is open, axle is not engaged and in 2WD mode
-If you see 12V switch is closed, axle is engaged for any 4WD mode.

You can also disconnect connector, meter leads across switch pins, KOER, in 2WD switch should show open, 4WD should show continuity.

 

I thought you meant what you meant, but then I second guessed myself - I appreciate the quality scrawl; definitely eliminated any remaining confusion.

So before doing any probing, I finally got my hands on another TCSCM which I've shown on the left in the attached picture. The gear ratios and some of the numbers didn't match so I didn't attempt to start the engine, but nonetheless when swapped in it does the same thing as the orginal - red neutral, then some grinding / clicking followed by the 4low selection flashing.




Now onto probing things.

okay with the red lead to the B+ terminal the E1 Tan lock solenoid wire shows 0.12v while in 4low. Pressing the brake raises the voltage to 0.16 - pressing any of the 4x4 buttons gets no response. However when the key is first turned there is a voltage spike that climbs to 9.5v before dropping back down to 0.12v.

Turning the key on/off and shifting between neutral and park gets the TCSCM to fire the motor and attempt to shift. During this I see 9.5v on the lockout circuit, accompanied by the grinding /motor firing sound and some clicking from the TCSCM.

I crawled under the truck and probed the C1 Tan wire, found voltage fluctuations in accordance to the same conditions above. So it's not the lockout solenoid?

here's a video of it attempting to shift.


My only guess is that I put too much gasket maker around the encoder motor shift shaft. Dont really want to pull the shaft and encoder motor again but what can you do 🤷‍♀️.

As for probing the AWD Indicator switch - it'll have to wait until my new actuator comes in on Saturday, as currently the only way for me to actually move the thing into 4x4 is to have the cable removed and to pull on it by hand.

 

I went back and took time reading thru all of your posts again. Along with looking at your scan tool images I am noticing a couple things that don't make sense. Just an example, I assume you weren't moving yet there are RPM's for both your front and rear prop shafts?

I couldn't tell for certain from the video, but I thought maybe I heard a binding...can't be certain. Either way, I'd like to get you back to a baseline and and use your tool to see where you are fresh. Give me some time to write it up and check a few things.

In the meantime if you want to check both prop shaft speed sensors, you can disconnect them and measure resistance on each. They should be between 1300-2700 ohms.

Also, I mistakenly told you to run that last test KOEO...should have been KOER. I believe TCSCM won't supply the ground when shifting out of 4LO unless KOER...but don't worry about it for now...let's get back to base first.

P.S. I would have used the correct gasket, not gasket maker.

 

There's RPMs because all the wheels are off the ground and I had the engine on at the time - can't recall if it was in neutral or drive at the time.

Yeah I should've gotten the proper gasket.

 

I’ve been spending time trying to find a verification for a ENCODER CIRCUIT table I put together based off info you could use while watching your scan tool for each mode/range. I have not been able to find a verification so I’ll give you what I have.

But first I wanted to have you get back to a baseline by having everything connected and all codes cleared and then watching your scan tool which may help point in a direction.

Inspect connectors and pins at TCSCM. Disconnect C1 & C2 from TCSCM. Look very closely for any contacts in connectors spread more than others, look for discolorations, green crusties, evidence of any burning (brown, black coloring melting). Inspect pins and contacts carefully.

Go ahead hook everything up and clear any codes and verify they are cleared (key off, key on, reconnect scantool and verify no hard code returned).

I’d probably then try to get it out of 4LO the normal way. Since you haven’t been having success getting out of 4LO with just truck running, trans in neutral, foot on brake…there are times when I have had to get mine out of 4LO by driving forward and/or reverse a few yards while selecting 2HI. Maybe try that first instead of trying to get it out by just sitting still (if you haven’t already).

After that, scan for codes. If a code is present, that would be the direction to first take, check for pending codes also. If a code is present, that would be the first direction to go.

If unable to get out of 4LO, and no codes present, go to scan tool live date like you did before (truck running, in neutral, foot on brake). Watch the PIDS as you attempt each selection:

Does the COM MODE INDICATOR match your selection? LIGHT? MODE SWITCH SELECTED?

Does the ENCODER GEAR POS ever come off “4WD LOW”?

Does the TRANSFER CASE LOCK state change based off your inputs?

Does the PARK SWITCH show OPEN? (since your trans is in Neutral)?

Does the FRONT AXLE REQ show YES in all modes except 2WD & NEUTRAL?

Are your PROPSHAFT SPEEDS showing more than 0 RPM (since you aren’t moving)?


The encoder table I put together based off one source, which I can’t find a verification from another source is below (maybe someone on here can verify):

Personally I would probably put a chart together answering all the questions above for each mode/range selection. Sometimes writing things down make something pop out to me.

Finally after all this, I would scan for codes again and then follow the service info testing for a specific code you can find in Alldata (or someone has already posted them on here you can search for).

All this would be my baseline to get me started.

NOTE: Since that motor lock seems it might be suspect…in addition before I started running thru the PIDS on the scan tool, I would probably hook up my meter like the drawing I posted and watch that along with the scan tool data to see if the TCMCS grounds the circuit when it should, especially with the codes initially cleared.

Just to add, I also found a couple good articles while I was searching this morning for a confirmation on the table on the 246...though it's not the 236 much of the articles is very relevant on the system for better understanding. Links below:

https://www.transmissiondigest.com/a...transfer-case/

https://www.transmissiondigest.com/n...ng-the-tricks/

 

So I think I got closer to the issue today..
Ran some errands and the vehicle died in the local gas station parking lot. Just click flat dead- no crank no start, flagged down a passersby and had jumpers on the battery- removed the starter relay and used a small wire to jump the start directly - nothing.

gonna get it (flat) towed home in the A.M,
if it's not a bad starter I'm certain it's the Neutral Safety Switch. I read on one of the other "stuck in 4x4" posts that the NSS communicates with the TCSCM. And I did a really shoddy job gluing the new NSS in - and I already have a replacement plug on hand, I just got lazy and didn't want to do the awkward soldering job.

Once I've got it running again I'll run through your recommendations and record everything.

I've also booked myself in at a local mechanic for Monday, if he does figure it out I'll be sure to update the thread with his findings.

 

You are driving around doing errands with your transfer case stuck in 4LO on dry blacktop?? What speed were you getting up to?

I have run across a TSB before that states the sealant on some auto trans vehicle plug does melt and glues it together. TSB stated for techs not to reuse that connector but rather to replace it. I can't remember if Blazers were included in that TSB or not.

Please go back and review post #15. I made a correction to the order voltages were listed for the selector switch from my original source. It is obvious they do not have it listed the same as the resistance measurements. This was apparent based off not only your measurements, but also one of the articles I linked.

 

I wasn't going above 50kph, and it was only a few km round trip. Got the starter out, it was dead as a doorknob. New starter is in, it runs and it's back in the air - first thing tomorrow I'll be getting back to work diagnosing things.