4wd disconnect - what are the signs of failure?

[Maverickxeo]

I just seem to get rotten luck with the 4WD system on my 04 Envoy.

Today, I noticed I doing some shopping and noticed when I backed out of parking stalls and turned left, my envoy would 'click' once really loud. I then noticed that I was 'stuck' in 4wd (despite being in 2wd physically) on the 4wd switch. I tried to switch back to 2wd, but it would just switch to 4wd again. I tried A4wd, and I could stay in that mode, but it would still make the 'click' when backing out and turning.

I got home, tried a different switch, and it still did the same thing. I tried 4LOW and neutral - both of which would not work and it would default back to 4hi. I disconnected the battery and pulled BOTH fuses for the 4wd system (48 for the disconnect and 8 for the ATC) and tried it again with no luck. I noticed when going to A4wd, the encoder motor worked a LONG time, far longer than normal. Going to 4wd was a 'quick' shift from A4wd. When pulling the fuse for the ATC, I can hear the disconnect working, but I DON'T hear it working when trying to shift into 2wd.

To continue investigating, I followed a guide here, about checking the front wheels. The left front wheel spins freely when in 4hi or A4wd, and the driveshaft does NOT spin. I lifted the right front tire and it spins freely without the front left spinning. I physically checked the driveshaft, and it was NOT free spinning - so the transfercase does seem to actually be in 4wd or A4wd.

I then went out on the road in front of my house (which is packed snow). In both 4wd and A4wd, there was no crowhopping while doing very sharp u turns in both directions. I did occasionally hear the 'click' as described earlier. I tried flooring it, and neither front tire spun.

I am stuck here now. I am heavily thinking that the front axle disconnect is causing all the problems, but I am not 100% sure. I did change the encoder motor for a separate problem a few months ago, though.

To put it simply - would a bad front disconnect cause the Envoy to 'force' itself to stay in 4wd, even when the disconnect is apparently 'disconnected? Would a bad disconnect not actually allow the transfercase to shift?

 

[TJBaker57]

When you were following the troubleshooting guide and spun a front wheel was the other front wheel on the ground? If both front wheels are simultaneously off the ground the test is invalid.

So if you spin the drivers side wheel with any 4wd mode selected with a solid position indicator at the selector switch, and the passenger side front wheel is on the ground, and while spinning the drivers side wheel the front propshaft does not spin then most likely the front axle disconnect is not engaging. The fault could be the electronic actuator for the disconnect or a mechanical failure inside the disconnect.

would a bad front disconnect cause the Envoy to 'force' itself to stay in 4wd

No, it cannot. If your switch is at 2Hi and the TCCM has the 4Hi indicator on (the switch itself does NOT control the indicator lights) then the trouble is with the TCCM, the encoder sensor inside the encoder/motor, the electric brake of the enocoder/motor, the encoder motor itself, or the wiring. One more less likely possibility is a mechanical failure inside the transfer case that prevents any movement of the shift mechanism.

What was the reason for the replacing the encoder/motor?

 

[Maverickxeo]

When you were following the troubleshooting guide and spun a front wheel was the other front wheel on the ground? If both front wheels are simultaneously off the ground the test is invalid.

So if you spin the drivers side wheel with any 4wd mode selected with a solid position indicator at the selector switch, and the passenger side front wheel is on the ground, and while spinning the drivers side wheel the front propshaft does not spin then most likely the front axle disconnect is not engaging. The fault could be the electronic actuator for the disconnect or a mechanical failure inside the disconnect.




No, it cannot. If your switch is at 2Hi and the TCCM has the 4Hi indicator on (the switch itself does NOT control the indicator lights) then the trouble is with the TCCM, the encoder sensor inside the encoder/motor, the electric brake of the enocoder/motor, the encoder motor itself, or the wiring. One more less likely possibility is a mechanical failure inside the transfer case that prevents any movement of the shift mechanism.

What was the reason for the replacing the encoder/motor?

Thank you for the response - I spun the driver wheel in the air in 4wd with the passenger on the ground. I then lifted up both tires and spun the passenger side - and the driver tire did NOT spin.

As for the reason for replacing the motor - it basically did the same thing before, where it wouldn't shift out of 4hi - it did fix the problem (for a months it seems - more on that shortly).

I want to add that I physically grabbed the passenger axle this morning (as I had time to actually do more investigating) and found that the CV is VERY loose at the disconnect - so I'm assuming the disconnect is shot one way or another.

As for the initial issue - I did a bit of reading and pulled the encoder motor off the transfercase. I attempted to shift the transfercase by hand, and it seems to shift okay (It doesn't want to 'stay' in place, if that makes sense). I then tried shifting using the switch with the motor hanging, and the motor worked - going to 2wd - but only once. I tried it a few more times and it would do what it was doing before, so I'm assuming I got a dud of a motor.

For what it's worth, I've ordered a new front disconnect, disconnect actuator (mine is covered in oil/grease/etc), and a rebuilt motor (the original motor I got was a new Dorman - I'm going with a reman Cardone this time).

 

[TJBaker57]

Thank you for the response - I spun the driver wheel in the air in 4wd with the passenger on the ground. I then lifted up both tires and spun the passenger side - and the driver tire did NOT spin

The critical part would be, did the front driveshaft spin while you were spinning the driver's side wheel with the passenger tire on the ground. I see you tested the front driveshaft and found it could not be turned and have further discovered looseness in the outer bearing of the disconnect so it would at least seem
as though you have a failed outer seal and bearing in the disconnect and that can cause further damage inside the disconnect.

It doesn't want to 'stay' in place, if that makes sense).

It makes perfect sense. That is why the encoder/motor has an electric brake inside it to prevent unwanted movement.

then tried shifting using the switch with the motor hanging, and the motor worked - going to 2wd - but only once.

Personally I would never do this as there is nothing to stop the motor from turning beyond it's design range which could damage the position sensor inside the encoder/motor.

Do keep in mind that faults can very well lie in the wiring that connects this whole system together. When that is the case one could replace every component in the system and still not resolve the issue.

 

[Mektek]

"there is nothing to stop the motor from turning beyond it's design range which could damage the position sensor inside the encoder/motor."

If memory serves, the encoder is perfectly round and there is nothing harmful with spinning it around completely.

 

[TJBaker57]

"there is nothing to stop the motor from turning beyond it's design range which could damage the position sensor inside the encoder/motor."

If memory serves, the encoder is perfectly round and there is nothing harmful with spinning it around completely.

I have seen a few different designs.

Inside the sensor are those wipers that travel across the resistive material, picking up the signal voltage to be sent to the TCCM.

On the sensor there is an area between the 5 volt end of the voltage dividing resistive material and the 0 volt end of same that under normal operations these wipers will never travel.

On at least one of those designs this area was not smooth. The wipers could be damaged if they got caught and bent back.

as I stated, personally, I would not do it.

 

[Maverickxeo]

So update:

Tried a new (rebuilt) encoder motor.... didn't do anything at first and tripped a code. Took it apart and found TAPE in the actual motor part and the encoder ring was missing half of it... used my old encoder ring and removed the tape and the shift motor worked. It shifted flawlessly.

As for the disconnect - after some struggling, I got the old one off. There are NO BEARINGS in the thing. They are... gone - completely turned to dust. Before removing it, I was able to move the axleshaft a LOT - easily over an inch at the disconnect end. After swapping in the new disconnect, the axle works as it should. There is also no 'clunking' either anymore.