Couldn' t select 4w lo, now what?

[budwich]

I seem to have fallen in a hole... :-(
I needed to change my engine oil in prep for a long trip (15% left on dic). Went to engage 4w lo to drive up ramps. Heard what sounded like actuator noises along with 4w lo light flashing (in neutral). Eventually, flashing stops, light status goes back to "4w hi" (not 2w which was original start state).
Try selection again, still no success. Decide to go up ramps in 4w hi... not that it will do much since there won't be any speed / clutching required.
Don't recall but I think I selected 2w and light flashes then selects 2w.

Change oil. Back down the ramps. Decide to try 4w lo again. Neutral, 4w lo flashing, don't hear much (not sure I was listening as close), light goes out but then "auto" is selected. Turn the selector to "2w". Flashing light but then "auto" stays selected. Now it appears that I can't get out of "auto".

Check fuses 8 (ATC) and 15 (TCM) with meter, good.

Changed the tranny and transfer case fluids in the fall as that vehicle had about 100k miles (bought used in the spring). Not sure of the maintenance history but the fluids looked (and smelled fine) and were at level. During the winter, things like traction control and such worked fine with no issues. Selected both 4w lo and "auto" in the over the winter with no issues. No trouble lights even now.

Probably look at the switch itself next, other suggestions along with double check of the transfer case fluids. I guess one question is will driving in "auto" in the summer cause issues.

Thanks for any additional suggestions.

 

[The_Roadie]

Wellllllllll.........

Assume you can distinguish the noises from the front axle actuator and the encoder motor. Can you try the various mode transitions with the engine off so you can hear the noises better? The 4LO transition takes a little longer then the others because the motor has to turn the control shaft through a larger angle.

I would not take a long trip while stuck in auto. But it's easy to disable by removing the front axle actuator from the disconnect and zip tying up in the air. And putting tape over the exposed hole. That way even if the TC tries to send torque forward, there's no place for it to go and the clutches won't get worn.

Root cause is probably the encoder motor. Like the switch, it may just need exercising a hundred times or so to clean up the position feedback sensor (the encoder) which works like a pot

 

[budwich]

thanks for the clues and suggestions. Tried disconnect the battery just ... just cause I had to wait for computer access...
Didn't help.

Checked the fluid level, good. Color good, smell ok.

On the encoder motor, does the "hammer technique" work (lightly of course) or is that the "wrong solution technique".

Will try the suggested "go thru modes" to see what I can hear.

 

[The_Roadie]

The encoder motor has permanent magnets inside that can shatter if hammered through the case. Better to listen for the right noises first, then decide to take it apart and check for broken gears in the planetary gear train that performs the reduction or a dirty sensor.

 

[budwich]

so while having some one turn the mode switch while engine off, neutral, and underneath to ensure where sounds are coming from. Can hear the encoder motor do some "electric buzzing" as one goes from mode to mode. I think there is a couple of "buzzes".... one when it tries to go to the selected mode and then one when the mode doesn't happen (ie. light stop flashing and auto lights back up) and it goes back to auto. However, I hear NO front actuator happening when the 4w lo is suppose to engage.... hmmm maybe the initial attempts tried to get the actuator to happen as I think I heard it on the very first attempt ("clunky") but there after nothing both in terms of changing back to 2W and subsequent attempts there after.


PS. By "buzzing", it mean motor "action"... its not the kind of noise that you would hear if the motor was "seized" but its also not like a "free running motor", more "selected turning".

Kind of related question... is it possible the actuator is stuck in some form such that the control doesn't know where so it has defaulted to "auto" to ensure that any clutch action can perhaps save things in the interim. Further, old GM system had some vacuum assisted switch in the front, but I assume that these are all electrical... right?

More questions.... can the encoder motor be "run" (powered / switched) while it is not installed on the transfer case to determine if it is operational or will this disturb any positioning sensors or cause a "run away" type condition (motor just keeps turning destroying things)?

 

[The_Roadie]

There are no vacuum controlled systems on our vehicles. And the A4WD mode isn't a default for any sort of failure. Each of the four modes should be a valid destination.

I've posted this so much over the years I'm honestly getting sick of it by now, but the front axle actuator ONLY makes noise in two mode transitions. 2HI->A4WD and A4WD->2HI. The encoder motor makes its noise in every possible mode transition.

If you hear buzzing, the motor could be jammed. Remove it from the side of the transfer case and run it in mid-air to see if the jam is in the motor or the transfer case. If only you had listened closely to the system when it was working well, you'd know if the sounds have changed. Also advice I've posted many times in the past.

But I understand not everybody reads all my posts except me.

Bench-testing the encoder motor has also been discussed three times in the last two weeks, with my advice and the schematics posted.

 

[budwich]

thanks again... no problem, the advice and "recant" is good. Coming from ford and older GM (s-10) so the experience is different. I hear no noise coming from the actuator at any mode. Next up, removal the motor and go from there.

 

[budwich]

Hey Roadie... one last question on this...

I read this in my GM repair guide

"Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode
Circuit Description
The transfer case brake control is supplied voltage at all times, with the key ON, through the B+ circuit. The brake control is activated when the transfer case shift control module registers the following modes:

• AUTO FWD

• 4HI

• 4LO

This is accomplished when the transfer case shift control module provides ground to the brake control through the T-Case Lock circuit. If there is a fault in the brake control circuit, the transfer case shift control module goes into a shift block mode. The shift block mode causes the mode indicator to flash for 10 seconds when another mode is selected. After the 10 second period has ended, the indicator reverts back to the previous mode selection. "

The symptom is kind of what has happened but I don't really understand what / how this works as I don't see any "brake control" lines coming into the transfer case shift control module related to the circuitry associated with the encoder motor. Does this "diagnostic symptom" make any sense?

Maybe it refers to an AWD system and not a selectable 4WD one.

 

[BRomanJr]

Hey Roadie... one last question on this...

I read this in my GM repair guide

"Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode
Circuit Description
The transfer case brake control is supplied voltage at all times, with the key ON, through the B+ circuit. The brake control is activated when the transfer case shift control module registers the following modes:

• AUTO FWD

• 4HI

• 4LO

This is accomplished when the transfer case shift control module provides ground to the brake control through the T-Case Lock circuit. If there is a fault in the brake control circuit, the transfer case shift control module goes into a shift block mode. The shift block mode causes the mode indicator to flash for 10 seconds when another mode is selected. After the 10 second period has ended, the indicator reverts back to the previous mode selection. "

The symptom is kind of what has happened but I don't really understand what / how this works as I don't see any "brake control" lines coming into the transfer case shift control module related to the circuitry associated with the encoder motor. Does this "diagnostic symptom" make any sense?

Maybe it refers to an AWD system and not a selectable 4WD one.

On your encoder there should be 4 heavier wires (2 for the motor and 2 to release the electric brake) if the brake is not releasing you won't get much movement, if any out of the motor/gearing.

If you remove the encoder from the TC and leave wires connected, changing modes should turn the output of the encoder.

 

[budwich]

Thanks for the added explanation. Outside of the diagnostic "blurb", there is no mention of this operation even in subsequent operation description and the schematics don't really show much labelling about this.

Got the motor off. Tried all positions of the switch, some noises from the motor but NO shaft / sprocket movement. :-( Might try and take it apart to see what I can see but it doesn't look good.

 

[Texan]

There is another recent thread with pictures of the encoder assembly taken apart. Sorry, I don't have a link.

Edit: probably in the drivetrain section.

 

[The_Roadie]

I assumed, but should mention it for the benefit of all, that the ORTB explanation is required reading for all wanting to understand the system:

http://www.offroadtb.com/articles/tech-docs/transfer-case-tech-the-nvg-226-np8-theory-of-operation/

 

[budwich]

thanks... that helps. I haven't found any photos or posts regarding the disassembling of the motor yet. Measured the resistances of the motor windings and lock circuit. Both have something so at least there is a circuit. Decided to at least pop off the "face cover". Nothing broken there although there is a outer black plastic ring around the perimeter of the sprocket that turns about 1/4 turn. Not sure if this is supposed to do that. I can't budge the sprocket manually... I guess that is good... means things aren't loose. Need to figure out how to get 12v onto the lock circuit to see if I can then manually turn sprocket.

With the motor removed (unplugged), the "service light" is on so I assume any conditions at the open plug like the ground for the lock won't happen. Have to check that at least the voltage is there (which it should be).

It would appear that perhaps the motor is toast since the TCCM isn't complaining when everything is plugged together.

Little update:

I used a power tool battery to active the lock... can hear it clicking when powered so that looks like it works, but I am still not able to manually turn the sprocket. When I measured the resistance of the motor, it was about .5 ohms (!) which could be alright but that means I need more than 25amp supply to drive the motor. Outside of the car battery, I don't have anything handy right now to do that with. Is the "ohmage" a little low?

 

[budwich]

I removed the position sensor (trim pot) from the motor housing. I got some strange measurements when I placed one test lead on one end contact pin and then slow moved the other test lead along the "resistance band". I was expecting a smooth rise as I moved away from the test lead connected to the contact pin but it wasn't so. Initially it started to rise but then about half way around it started to fall. This was for the outer band. Not sure what to make of that measurement / test. At points, jumped around in ohmage. I tried cleaning the areas but it didn't seem to help. Not sure what the coating / resistance material is to make it react in such a strange fashion.... or maybe the technique isn't so good.

 

[The_Roadie]

Sounds like you just need to clean the heck out of it or buy a new one.

 

[budwich]

I continue down the "hole". I got a "rebuilt encoder motor" from advanced auto. Plugged it in but not bolted on to the case so I could watch things. With key in on, move the selector thru positions, could see the sprocket turn on a couple of positions but not when going to 4w lo (4w lo flashed), I think normal (no motor movement) from readings. BUT now a couple observations. Although the auto light did go out during the initial "run" from 2 to auto to 4w hi. Once I got no 4w lo "completion" (ie. stayed flashing), then going back to 4w hi and eventually to 2w. The auto lit back up and is back on "permanently".... :-( Now, the motor is no longer moving with any selector change.... :-( and I have the problem of the motor sprocket potentially not aligning with the shaft of the transfer case because of the position of the "offset mark". Is there a way to cause the alignment / change in the transfer case shaft manually? Does the TCCM need to be reset / can it be reset? Of course, why is the motor no longer turning after one attempt going to 4lo?

 

[budwich]

The "hole" gets deeper... eek!. Of course, with truck off, pull atc fuse 8. Replaced fuse. Turn key to ON. Selector lights all come on then all go out. Now the "service icon" comes on which wasn't happening before with all things connected.

.... glub, glub, glub, glub... :-(

 

[budwich]

well, I see a warning in the service instructions which seem to allude to a couple of things.

One... "Important: Before the motor/encoder is removed, ensure that the motor/encoder is in the 2HI position."..... but what happens when the light only shows "auto" as selected and can never change to 2w hi.

Two... the above would seem to indicate that the motor should never be run when not connected to the shaft as then the positioning may never be aligned again.... which maybe where I am now stuck.

Is there a way back in terms of aligning to two components: transfer case and motor sprocket????

further taken from the overhaul of the transfer case:

"Important: The shift control detent must be in the NEUTRAL position when installing the motor/encoder." Does anyone know what position that might be on the shaft? Maybe if I am lucky, I might be able to electrical move the shift motor in the right direction to align things.

 

[budwich]

Found the neutral position for the transfer case which is the "offset" on the shaft pointing towards where the cabling connection / connector would be coming off the motor IF it were mounted. Now I just need to figure out how to move the motor sprocket back to that position for alignment. I suspect what happen is that with the motor off the transfer case and then moving thru the selector positions, the motor eventually moves to a position where the TCCM gets a reading that is totally fubarred and shuts things down. This would be the equivalent of getting a bad resistance reading (which may have likely been the original issue). IF this is true, then a BIG warning would be DO NOT run the motor when not engaged with the transfer case UNLESS you have a means of moving it back into the position that it came from. Hopefully, I can get it back there.

 

[BRomanJr]

Found the neutral position for the transfer case which is the "offset" on the shaft pointing towards where the cabling connection / connector would be coming off the motor IF it were mounted. Now I just need to figure out how to move the motor sprocket back to that position for alignment. I suspect what happen is that with the motor off the transfer case and then moving thru the selector positions, the motor eventually moves to a position where the TCCM gets a reading that is totally fubarred and shuts things down. This would be the equivalent of getting a bad resistance reading (which may have likely been the original issue). IF this is true, then a BIG warning would be DO NOT run the motor when not engaged with the transfer case UNLESS you have a means of moving it back into the position that it came from. Hopefully, I can get it back there.

All the feedback needed for the encoder is in the second harness (IIRC there are 2), were they both connected? There aren't any switches in the TC.

IMHO If it messes up while not bolted on, you still have an issue.

 

[budwich]

Well, I rounded up a spare battery (originally I had measured my original motor and windings indicated .5 ohms which might be OK for a motor winding... I didn't remeasure the new motor ... duh... but I assumed I would need a "few amps" to get the things turning) and hooked it up to the motor. Used a 12v tool battery to release the lock and aid with the wiring routing. Hit the motor a few times to bring it back to "neutral". Aligned the now "neutral" motor sprocket to the "neutral" transfer case shaft. Bingo, check light off, 2w hi light on at selector. Yippy! I haven't tried selecting anything yet as I need to tighten bolts back up.... but my fingers are crossed.

My take away in this is that there is an "out of range" resistance area that the motor should never get to IF it is connected to the transfer case because there are physical stops in the case. IF it does, then the TCCM "thinks" there is a significant problem with the transfer case and basically lights up the warning and shut down things as best it can.... so my warning is DO NOT run the motor disconnected from the transfer case unless you are able to find way to reposition it there after either manually or electrically.