TC Motor

ts684

Original poster
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May 29, 2013
81
Did similar with a 12v motorcycle battery, small female spade connectors and short pigtails. Don't remember if I tried to turn the TC shaft while trying to turn drive shaft but I might see if I can do that.
 

ts684

Original poster
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May 29, 2013
81
Replacement TC motor is a Dorman probably from either Rock Auto or Parts geek. Tried turning TC shaft CW. After 2WD there seems to be an almost spring loaded position, with vise grips on and a bungee cord applying pressure, it seems to be in A4WD or very close. With trans in neutral, turning rear driveshaft results in all wheels turning. I could not turn shaft CW past this point. With ignition on, engine off, same result as before. Turning to 4WD results in flashing over 4WD and steady over 2WD then service 4WD drive lite on dash.
One thing that was unexpected, with engine on, trans in neutral, when I turned the rear drive shaft by hand, it continued to turn by itself!!!
 

ts684

Original poster
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May 29, 2013
81
JUST WONDERING. I was at the U-Pull It yard the other day and found an Envoy TC on the ground, transmission was gone. Pulled the TC motor and tried turning the shaft. Found 4Lo full counter clockwise. Going clockwise to neutral and then 2HI. After this there was a "spring loaded" position that resulted in both rear and front drives turning. Does anybody know if there is an A4WD position and a 4Hi position, or if in A4WD does TC motor just turn clockwise as needed in response to slippage? If this is true, then my TC may be OK. So what else could be the problem? TCCM, TC motor sensor, something else? Just about ready to take to stealer for a diagnostic, but probably not repair.
 

TJBaker57

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Aug 16, 2015
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in A4WD does TC motor just turn clockwise as needed in response to slippage?

You have it right. That "spring loaded" region is A4WD where the shift motor starts at a predetermined spot and then the TCCM reacts to slippage as seen by the speed sensors. Full clockwise is fully 4Hi
 

ts684

Original poster
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May 29, 2013
81
OK, but can you turn clockwise to a position that is not "spring loaded", or does the TC motor just hold this position to give 4Hi?
 

TJBaker57

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Aug 16, 2015
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OK, but can you turn clockwise to a position that is not "spring loaded", or does the TC motor just hold this position to give 4Hi?

Given thete are no detents on the cam(s) in this image of the 4 Hi position I would have to surmise it is the brake in the shift motor that holds the 4 hi position. The brake is normally on, needing power to release to enable a shift of position.

4hi-flow.jpg
 
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budwich

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Jun 16, 2013
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if you go back to the link in the second post, it explains the operation of the cam. As was stated / viewed above, the cam is set in the same "relative position" for 4Hi AND A4WD as shown. It is not held in any position by any physical "detent" but the electric brake of the encoder. The difference in "actual position" between the two settings is one use a "pre-calibrated position" on the cam while the other sets itself by requested torque which is demanded and causes the cam to be moved "slightly" to adjust the "subtending clutch" giving more or less slip..... that my read.
 

TJBaker57

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Aug 16, 2015
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Here's something I did the other day for fun. I took a transfer case shift motor sensor and applied 5 volts to the sensor and then rotated the sensor to return the voltages as required by the TCCM for the various positions. Here are the initial A4WD and 4 Hi positions showing the location of the alignment tab of the sensor. As Budwich says,,, there isn't much movement between A4WD and 4Hi as you can see.

IMG_20200907_175428~2.jpgIMG_20200907_175456~2.jpg
 
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ts684

Original poster
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May 29, 2013
81
Ok. I hope this means that the TC is not toast. Maybe just sensor or TCCM?
 

ts684

Original poster
Member
May 29, 2013
81
Ok. I hope this means that the TC is not toast. Maybe just sensor or TCCM?
Well, went by the stealer to see if they could do a diagnostic on the TC. With virtually no one in a large service area, I was told that I would have to make an appointment and MAYBE they could get to it in about 2 weeks. Did they send everybody home for Covid? Don't they work far enough apart? I work for a regional grocery chain and all hands are on deck!

Anyway, went to the local U-Pullit yard and picked up a TC motor from a 08 TB and a TCCM from an 07 TB. Easy pick, it had the dash pulled. Went home and changed both, same result. Turning selector to A4WD, 4Hi, or 4Lo gave a flashing lite at that selection and a steady lite at 2WD. After a bit, service 4wd lite on dash. Probing Br/Wh return wire gave readings from 4Lo, 2Wd, 4Awd, and 4Hi of 0.7v, 2.7v, 3.48v, and 4.0v. The LtBl at C1 A6 gave 1.9v not 4 as expected, don't know what this means.

With motor running, trans in neutral, selector in 4Hi (flashing), I got under the car and manually turned the main driveshaft. All four wheels turned, so I guess something is happening since only rear turn in 2Wd.

Will try independent shop soon.
 

TJBaker57

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Aug 16, 2015
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LtBl at C1 A6 gave 1.9v not 4 as expected, don't know what this means.

That means you have either a bad switch or bad connection(s) somewhere between the TCCM and the switch. Switch return voltages should be close to these readings...

4Lo 1.59
Neutral 0.85
2Hi 4.06
A4WD 3.22
4Hi 2.42
 

ts684

Original poster
Member
May 29, 2013
81
That means you have either a bad switch or bad connection(s) somewhere between the TCCM and the switch. Switch return voltages should be close to these readings...

4Lo 1.59
Neutral 0.85
2Hi 4.06
A4WD 3.22
4Hi 2.42
Will check that again, wouldn't be the first time I got confused on color. Maybe take another trip to U-Pullit and get a switch.

On a related subject, I took apart the original TC motor. 4 levels of reduction gears and 1 missing tooth gumming up the works. The gearbox was dry, not a sign of any lube of any kind.
 

TJBaker57

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Aug 16, 2015
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Will check that again, wouldn't be the first time I got confused on color. Maybe take another trip to U-Pullit and get a switch.

On a related subject, I took apart the original TC motor. 4 levels of reduction gears and 1 missing tooth gumming up the works. The gearbox was dry, not a sign of any lube of any kind.

I have heard before that they might benefit from a re-lubrication. A loose tooth floating around in there certainly couldn't help matters.

The original switch can be opened up if one is careful. There are several little locks that if memory serves I propped open with little slivers of this or that while I worked the package open for cleaning. But if one is going through the bother of getting the dash apart to get at the switch it could be wise to just replace it. Of course I didn't, I still have a new one on hand as a spare after cleaning my original.

IMG_20190321_150817.jpg
 

TJBaker57

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Aug 16, 2015
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I just checked out a couple of TCCM I pulled from a couple yards. Firstly, if one is doing this don't assume it's not already been replaced. The 2003 I pulled looks to be original by the part number, however the 2002 I pulled is newer. Must have been replaced. I popped open the packages and removed the circuit boards for inspection. The 2003 looks superior in assembly to the newer replacement unit from the 2002! Specifically, there is a heat sink with these units and while the older part number had some adhesion from the board to the heatsink the newer part number did not. The newer unit just fell right out when I released the retaining clip while the older unit took a lot of gentle persuasion to get it free of the heatsink.

That aside it would be worth peeking inside right at the yard you are pulling the module from to avoid getting a fouled circuit board. This is what I found on the 2002 pull.....

IMG_20201013_110709.jpgIMG_20201013_110846.jpg

And here can be seen the adhesion to the heatsink on the 2003...enough good contact to leave impressions. The replaced 2002 was devoid of any such marks...

IMG_20201013_113508.jpg

The dash switch is cheap enough online but folks pull them from yards also. Or maybe you want to check out the switch you have. Granted, this requires pulling some dash panel but just in case someone besides myself were interested I checked out a used and a new switch I have on hand. Here are the resistances seen from Terminal M that supplies the reference voltage to Terminal J which is the return signal to the TCCM.

Screenshot_20201013-124209~01.png

And here is what the insides of the used switch looked like before I wiped it clean. The stuff there is likely a non conductive lubricant but I wonder if it could still interfere in some way given 10 or 15 years time...

IMG_20201011_111958.jpg
 

budwich

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Jun 16, 2013
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kanata
Your neutral reading on the used unit is a little high, possibly from lack of selection resulting in a bit more resistance in the path.
 

TJBaker57

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Aug 16, 2015
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Your neutral reading on the used unit is a little high, possibly from lack of selection resulting in a bit more resistance in the path.


I also noticed that selection had the greatest difference in resistance, both as raw values and as a percentage.

An additional piece of information missing from my post was that the old switch was first measured directly from the circuit board where the new one was measured from the terminal connections. In theory this should eliminate wear as a factor in the old switch, having bypassed the contacts slider altogether. I then followed up that test reading the same old switch through the terminal contacts and selector mechanism looking for variances due to the contact slider. None were found.

IMG_20201011_121006.jpg


What I "should have done", was measured the used junkyard switch BEFORE I wiped clean the contact pads!

Wonder what the acceptable range is. I once recorded video of a Tech 2 as the shift motor operated through the various selections. When I reviewed the video in slow motion I was surprised to see the value "2 Lo" flash by.
 
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TJBaker57

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@budwich you inspired me to do more to learn about this!! So I took the two junkyard TCCM I have and did a full set of resistance checks, recorded in spreadsheet of course. Found the internal resistance of the dashboard switch circuit of the TCCM (998 ohms), reacquainted myself with Ohms law applied to series resistance circuitry, and worked out the different expected return voltages of the used and new switches for all positions. Surprisingly if not suspiciously small!! The largest difference is 0.07 volts!

Screenshot_20201013-171905.png
 
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budwich

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Jun 16, 2013
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"Wonder what the acceptable range is.".... the GM SI gives a range for each position... that was the basis of the comment.

I added a sample of the gm si that I had come across.
 

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Mektek

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May 2, 2017
656
FL
Resistors typically have a 5% tolerance, so the values recorded between new and used are probably within spec. I resoldered the resistor connections and terminals (mostly for peace of mind) as the original lead free solder was prone to cracking with age, although I did not find it in this application.
And of course I replaced the bulbs with leds while I had it apart.
 

TJBaker57

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Aug 16, 2015
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What I was curious about was if there is an additional allowance of sorts for a variance of the resultant voltage read by the TCCM when determining what particular mode one is in.

So to be considered as being in 2Hi for instance, what is the acceptable switch return voltage seen by the TCCM? If I calculate the value using only the maximum and minimum voltages (5.2 to 4.8) allowed along with the maximum and minimum resistances (245 to 230) I come up with 4.23 => 2Hi => 3.85.

Calculating for all positions shows me there would then be at least 0.44 volts between positions.


Neutral 0.83 to 0.95
4Lo 1.51 to 1.71
4Hi 2.28 to 2.54
A4WD 3.04 to 3.41
2Hi 3.85 to 4.23

Edit: this needs an edit! Pasted something wrong in here! (Found it)
 
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TJBaker57

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Aug 16, 2015
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And here is an unexpected finding while examining the TCCM. Tabletop testing of resistances on a couple of these revealed the two grounds of the device are not directly shared internally. Between the two grounds I measured 82.2k on one unit and 83.9k on the other unit. Once installed these two grounds are connected through the vehicle chassis using two different attachments. The larger C3-A goes to sp201 at right front of lower console and the C1-B8 goes to G102 in the engine compartment by the rear of the fuseblock.

So when evaluating TCCM troubles one needs to verify two different chassis ground points.
 

budwich

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Jun 16, 2013
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kanata
I think that might be sort of an "over specification" (return voltage range). IF the resistance and reference voltage is "spec'd", then "electrical math" has set the rest. Further, the resistance test can be done "unplugged" along with the reference voltage while any other might need to "impinge" on the wiring via potentially "less than good connectivity" (depending on the technique used).
 
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budwich

Member
Jun 16, 2013
2,027
kanata
And here is an unexpected finding while examining the TCCM. Tabletop testing of resistances on a couple of these revealed the two grounds of the device are not directly shared internally. Between the two grounds I measured 82.2k on one unit and 83.9k on the other unit. Once installed these two grounds are connected through the vehicle chassis using two different attachments. The larger C3-A goes to sp201 at right front of lower console and the C1-B8 goes to G102 in the engine compartment by the rear of the fuseblock.

So when evaluating TCCM troubles one needs to verify two different chassis ground points.
maybe somewhat expected as possibly "power ratings" and other requirements (ie. isolation, back feeding, etc). One (heavier) for power feeding requirements and the other for signals.
 
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TJBaker57

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maybe somewhat expected as possibly "power ratings" and other requirements (ie. isolation, back feeding, etc). One (heavier) for power feeding requirements and the other for signals.

Yep! The heavier one feeds the shift motor circuit. The lighter one grounds the control circuitry. I guess the takeaway here is to verify both grounds and not think that checking one ground circuit is "good enough".
 

TJBaker57

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Aug 16, 2015
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Colorado
here can be seen the adhesion to the heatsink on the 2003...enough good contact to leave impressions. The replaced 2002 was devoid of any such marks...


A followup is necessary here. Upon revisiting this I can now see the differences better. The older 2003 unit had a protective coating applied to the entire circuit board, including between the board and the heatsink. The newer replacement unit had the protective coating left off the heatsink area of the board. So in reality the newer board may have better thermal transfer to the heatsink! Things are not always what they first appear to be!
 

TJBaker57

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Aug 16, 2015
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I think that might be sort of an "over specification" (return voltage range). IF the resistance and reference voltage is "spec'd", then "electrical math" has set the rest. Further, the resistance test can be done "unplugged" along with the reference voltage while any other might need to "impinge" on the wiring via potentially "less than good connectivity" (depending on the technique used).


I guess I am looking at this from the standpoint of ease of testing, which I agree is not necessarily the ideal approach. With nothing more than popping off the left side dash access cover and backprobing the TCCM light blue C1_A6 terminal I can quickly get the switch return voltage. Easy peasy, no need for pulling the dash open to access the back of the switch for a resistance test. And though it has not worked for others, on my 2002 I can read the value of the switch return in Torque Pro. This is what drives me to define the switch return voltage as best as I can.

I suppose I could also pull the TCCM connectors and do a resistance test through the wiring but then as you say we are introducing potentially "less than good connectivity" of the wiring connections in this way. However, that is what the TCCM is seeing and basing it's actions on, the whole circuit.

It's a tricky business this electrical stuff. You can pull a connector and test a ground with an ohmmeter but does that mean the ground will hold up under a full load? Nope. Only thorough, detailed, logical testing under real-world conditions has any chance of leading one to a definitive diagnosis. And even then we have to deal with the possibility of flaky software!
 

ts684

Original poster
Member
May 29, 2013
81
IT WAS AN "O" RING!!!!! First, I would like to thank every body who posted suggestions, I learned more about GM 4 wheel drive than I ever thought I would. Got it fixed in mid November, but just got around to posting now. First the front axel disconnect actuator was bad, so I replaced it. Second the original TC motor was bad, a tooth was broken off in the reduction gears, didn't know that till later, replaced. Still flashing lites and service 4WD. So I took it to an independent shop. Picked it up the next day and was told that a scan indicated a problem with the axel disconnect actuator. When they took a look, they found a slow drip of coolant was hitting the actuator. So they said they replaced the actuator and oh yea, the one I installed was missing an "O" ring. So as I'm leaving wondering how if it was the coolant, why didn't in work when I first installed. Then it hit me, the "O" ring. Not only does it provide a seal, it also spaces the actuator out a bit. Without it, when activated, the plunger cannot go out as far as it should which results in an error message!! All is well now, at least with the TC.
 

TJBaker57

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Aug 16, 2015
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Well now that is curious. I wonder if not all actuators are built the same as mine has a spring loaded plunger. So even when my fork could not travel due to internal damage my actuator motor went full travel and siganlled the OK back to the TCCM when in fact the shift was unsuccessful. The coil spring in mine can be seen circled in this picture...

1416091993372_20210102162403596.jpg
 

ts684

Original poster
Member
May 29, 2013
81
Well with missing the "O" ring, that was not included with the actuator I received, the plunger would not move as far as it should. Your plunger moved the full range but did nothing since the fork was broken. If the plunger was stuck, or couldn't move far enough that would create an error situation. Sound right? Wish I didn't toss the original actuator, the "O" ring was probably buried in the oily crud.
 

TJBaker57

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Aug 16, 2015
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Colorado
Your plunger moved the full range but did nothing since the fork was broken


Well actually no, my plunger did not move.

On mine the motor mechanism of the actuator pushed against the coil spring inside the plunger but the plunger could not extend because a worn out thrust washer fell into the path of the shift fork/collar and prevented its motion. I theorize this is a precaution built into the actuator/plunger such that if the gears are not properly aligned for the collar to slide over them both, the coil spring then absorbs the motion of the actuator, and when there is a little rotation of the gears and they get aligned the spring then completes the shift.
 

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