Will only switch out of 2wd in neutral

[WestCoastie]

I have an 03’ Yukon XL

When I bought the truck about a year ago everything 4x4 worked. I don’t use 4 wheel often so not sure when the problem occurred.

Now, the only way to shift into 4wd Auto, 4HI, 4LO and back into 2wd is in neutral.

If I try to change into 4Auto while moving the light blinks for a long time and then eventually switches over, though not sure it actually engages. When I press 2wd to switch back, it blinks for a long time and never actually switches back, service 4wd comes on.

I have already replaced encoder motor. I did buy another switch from Amazon. So if that doesn’t work, easy return.

Other than that not sure where to go from here. Thanks!

 

[B-train]

Check the tire brand, size, and wear. They should all be the same and equal wear. Binding driveline will occur with different circumference tires

 

[NickTransmissions]

I have an 03’ Yukon XL

When I bought the truck about a year ago everything 4x4 worked. I don’t use 4 wheel often so not sure when the problem occurred.

Now, the only way to shift into 4wd Auto, 4HI, 4LO and back into 2wd is in neutral.

If I try to change into 4Auto while moving the light blinks for a long time and then eventually switches over, though not sure it actually engages. When I press 2wd to switch back, it blinks for a long time and never actually switches back, service 4wd comes on.

I have already replaced encoder motor. I did buy another switch from Amazon. So if that doesn’t work, easy return.

Other than that not sure where to go from here. Thanks!

Check underneath to see if wires to the encoder motor assembly got cut or damaged.

Also, when you replaced the sensor, was there already a t case code stored (service 4wd displayed)? If so, did you clear the code? Asking as I recently replaced my motor assembly (03 tahoe) and that was necessary for me to get everything working again.

 

[WestCoastie]

Not sure that’s the issue.

Check underneath to see if wires to the encoder motor assembly got cut or damaged.

Also, when you replaced the sensor, was there already a t case code stored (service 4wd displayed)? If so, did you clear the code? Asking as I recently replaced my motor assembly (03 tahoe) and that was necessary for me to get everything working again.

I didn’t replace any sensor, unless you are referring the the encoder motor assembly. While I was down there I looked at wires and they looked fine. Everytime I turn the truck off and then back on the service 4wd goes away. It only shows up if I try to switch to anything while moving. Doesn’t show up when switching in neutral.

Are you saying the code might still be present and need to be cleared anyway?

 

[NickTransmissions]

Not sure that’s the issue.

I didn’t replace any sensor, unless you are referring the the encoder motor assembly. While I was down there I looked at wires and they looked fine. Everytime I turn the truck off and then back on the service 4wd goes away. It only shows up if I try to switch to anything while moving. Doesn’t show up when switching in neutral.

Are you saying the code might still be present and need to be cleared anyway?

my bad, meant to say encoder motor. I also replaced the encoder motor sensor in my old encoder motor assy but that didnt fix the problem as motor assembly itself was bad.

I had the exact same issue as you now have until I cleared the t case encoder motor code.

Clear the code and let us know what happens.

 

[Fless]

Let us know how the switch replacement works. There is an easy procedure to measure the various switch position ohm values.

To focus on the specific cause you'll need to use a scanner that can read the 4wd codes. When the DIC says "Service 4wd" there is a code in the system that will help point you to the cause.

For examle, there are typically several speed sensors on the transmission and transfer case, and those work together to manage the transfer case prop shaft speed (especially in AUTO). The wheel speed sensors should also be reporting the correct wheel speed, with all four tires the same size and similar wear.

EDIT: I would also add to check AND CLEAN the grounds that are associated with the 4wd system. Specifically, Ground Zone 10 on the corner of the dash, passenger side; and Ground Zones 21a and 21b on the body mount just behind the left rear tire. I've attached a zoom-able ground zone map. Also check and clean the main ground strap connection from the driver side head to the firewall; OE is a braided strap.

Diagram of grounds 21a and 21b:

 

[NickTransmissions]

Here's the procedure from the 2003 FSM

 

[WestCoastie]

Let us know how the switch replacement works. There is an easy procedure to measure the various switch position ohm values.

To focus on the specific cause you'll need to use a scanner that can read the 4wd codes. When the DIC says "Service 4wd" there is a code in the system that will help point you to the cause.

For examle, there are typically several speed sensors on the transmission and transfer case, and those work together to manage the transfer case prop shaft speed (especially in AUTO). The wheel speed sensors should also be reporting the correct wheel speed, with all four tires the same size and similar wear.

EDIT: I would also add to check AND CLEAN the grounds that are associated with the 4wd system. Specifically, Ground Zone 10 on the corner of the dash, passenger side; and Ground Zones 21a and 21b on the body mount just behind the left rear tire. I've attached a zoom-able ground zone map. Also check and clean the main ground strap connection from the driver side head to the firewall; OE is a braided strap.

Diagram of grounds 21a and 21b:

View attachment 404677

Thank you, I’ll try and get those codes checked and cleared.

All those grounds are good except the one in dash I have not checked. I’ll try it as well.

Also, all 4 tires and wheels are the same size, but front aren’t damn near bald and rear almost new. Couldn’t be helped, just how it worked out. Should be fixing that soon.

 

[DirtDigler]

Maybe I'm not understanding your post but you're supposed to be in N when you change to 4H ,4L, and back to 2H. As for Auto, the only time I used it, I engaged it while climbing a hill then I lost my front diff. The fork got bent I assume it's because I was moving while it kicked in. I know, it's Auto, it should work automatically! Needless to say I'll never use Auto again.

 

[WestCoastie]

Let us know how the switch replacement works. There is an easy procedure to measure the various switch position ohm values.

To focus on the specific cause you'll need to use a scanner that can read the 4wd codes. When the DIC says "Service 4wd" there is a code in the system that will help point you to the cause.

For examle, there are typically several speed sensors on the transmission and transfer case, and those work together to manage the transfer case prop shaft speed (especially in AUTO). The wheel speed sensors should also be reporting the correct wheel speed, with all four tires the same size and similar wear.

EDIT: I would also add to check AND CLEAN the grounds that are associated with the 4wd system. Specifically, Ground Zone 10 on the corner of the dash, passenger side; and Ground Zones 21a and 21b on the body mount just behind the left rear tire. I've attached a zoom-able ground zone map. Also check and clean the main ground strap connection from the driver side head to the firewall; OE is a braided strap.

Diagram of grounds 21a and 21b:

View attachment 404677

Thank you, I’ll try and get those codes checked and cleared. Will a regular OBD2 scanner work or do I need one of those fancier ones

All those grounds are good except the one in dash I have not checked. Is there anywhere to see more graphics like the one you sent? The zone map is helpful in pointing to the area but doesn’t specify exactly where the grounds are. I think I’m just going to try and clean them all up if I can.

Tomorrow I can definitely get the switch swapped out. I’ll let you know if that does it.

 

[WestCoastie]

Maybe I'm not understanding your post but you're supposed to be in N when you change to 4H ,4L, and back to 2H. As for Auto, the only time I used it, I engaged it while climbing a hill then I lost my front diff. The fork got bent I assume it's because I was moving while it kicked in. I know, it's Auto, it should work automatically! Needless to say I'll never use Auto again.

Right, I don’t exactly have a problem swapping into 4HI and 4LO and back to 2wd. As you said that part is working properly. But shifting into 4Auto I shouldn’t have to be in neutral, but that’s the only way I can get it to work now.

I used to have an 01’ 2500 with the 6.0 and it had 4Auto. It worked flawlessly and I never had a problem. The Yukon use to work fine, just decided to stop doing that I guess.

 

[Fless]

Maybe I'm not understanding your post but you're supposed to be in N when you change to 4H ,4L, and back to 2H. As for Auto, the only time I used it, I engaged it while climbing a hill then I lost my front diff. The fork got bent I assume it's because I was moving while it kicked in. I know, it's Auto, it should work automatically! Needless to say I'll never use Auto again.

Not on the later transfer cases like the OP has. This is an '03 and the only time he should need to have the tranny in neutral to change modes is to go in and out of 4LO. Every other mode change is on the fly.

 

[Fless]

Thank you, I’ll try and get those codes checked and cleared. Will a regular OBD2 scanner work or do I need one of those fancier ones

All those grounds are good except the one in dash I have not checked. Is there anywhere to see more graphics like the one you sent? The zone map is helpful in pointing to the area but doesn’t specify exactly where the grounds are. I think I’m just going to try and clean them all up if I can.

Tomorrow I can definitely get the switch swapped out. I’ll let you know if that does it.

You'll need a bit more advanced code reader; the typical scanner won't read those codes. Sometimes the auto parts stores will have one of those to use.

 

[B-train]

Thank you, I’ll try and get those codes checked and cleared.

All those grounds are good except the one in dash I have not checked. I’ll try it as well.

Also, all 4 tires and wheels are the same size, but front aren’t damn near bald and rear almost new. Couldn’t be helped, just how it worked out. Should be fixing that soon.

Got burned as a young tech for a K2500 that wouldn't shift out of 4wd except for when in neutral. It was warranty and I went through the whole TC (did find some worn parts from binding). Put it back in and thought I had it, but then it acted up the same way.

Called a buddy of mine who is a master GM tech for 35 years and he asked about tires. I was a little confused at first but told him the size and condition- same as yours. He said swap one side front to back. Viola!

Worked perfectly, I felt dumb, but learned a good lesson that has never left me. I encourage you to give that a try and see. Then get a new matched set of tires and keep them rotated.

 

[WestCoastie]

Got burned as a young tech for a K2500 that wouldn't shift out of 4wd except for when in neutral. It was warranty and I went through the whole TC (did find some worn parts from binding). Put it back in and thought I had it, but then it acted up the same way.

Called a buddy of mine who is a master GM tech for 35 years and he asked about tires. I was a little confused at first but told him the size and condition- same as yours. He said swap one side front to back. Viola!

Worked perfectly, I felt dumb, but learned a good lesson that has never left me. I encourage you to give that a try and see. Then get a new matched set of tires and keep them rotated.

Never would have thought that would matter that much. So basically just swap front for back?

Also, tires are only that way because when I bought it front had a little life left, and rear were completely bald. Didn’t have money at the time for all 4 and I hate the stock rims, so I planned on doing everything when I could get new wheels. Skip to now when I get new wheels and figure out they are lug centric… now I have to get an adapter… then all new tires

 

[B-train]

Never would have thought that would matter that much. So basically just swap front for back?

Also, tires are only that way because when I bought it front had a little life left, and rear were completely bald. Didn’t have money at the time for all 4 and I hate the stock rims, so I planned on doing everything when I could get new wheels. Skip to now when I get new wheels and figure out they are lug centric… now I have to get an adapter… then all new tires

Just switch one side of the truck front to back. This will allow the rolling circumference differences to be equalled out by the open diffs.

With different circumference tires, one set will be covering more ground than the other 2 and then they fight each other when locked in 4wd. It's either trying to stretch your truck, or accordion it depending on the situation. LOL

 

[WestCoastie]

Just switch one side of the truck front to back. This will allow the rolling circumference differences to be equalled out by the open diffs.

With different circumference tires, one set will be covering more ground than the other 2 and then they fight each other when locked in 4wd. It's either trying to stretch your truck, or accordion it depending on the situation. LOL

Ok, I’ll get there when I can. Tried swapping out the switch and it made no difference, but that’s easier than swapping tires around.

When I did get it to swap into 4Auto it really sounds like it’s binding up. Not sure if that’s because of the tires, it needs oil in that front diff or something else.

I’ll report back as I try things. Thanks again

 

[rockola1971]

Ok, I’ll get there when I can. Tried swapping out the switch and it made no difference, but that’s easier than swapping tires around.

When I did get it to swap into 4Auto it really sounds like it’s binding up. Not sure if that’s because of the tires, it needs oil in that front diff or something else.

I’ll report back as I try things. Thanks again

If you are in Auto 4WD the Tcase should not physically be in 4wd UNTIL there is a wheel speed difference detected via the front/rear driveshaft speed sensors which means you have wheel slippage. So if you are actually in AUTO 4wd and the Tcase is in 4wd (which means the clutches are engaged within the Tcase in the Auto section) then you have an internal problem within the Tcase OR the computer is getting false information from the driveshaft sensors that you have wheel slippage. See the attached NP246 Tcase writeup. I believe you are getting false information to the Tcase because in order for the vehicle to be truly in 4wd from Tcase to the front wheels the front axles have to be engaged and that would need an active command for 4wd UNLESS you have 2 faults happening and your front axles are engaged at the front diff because of a mechanical failure at the actuator.

 

[WestCoastie]

If you are in Auto 4WD the Tcase should not physically be in 4wd UNTIL there is a wheel speed difference detected via the front/rear driveshaft speed sensors which means you have wheel slippage. So if you are actually in AUTO 4wd and the Tcase is in 4wd (which means the clutches are engaged within the Tcase in the Auto section) then you have an internal problem within the Tcase OR the computer is getting false information from the driveshaft sensors that you have wheel slippage. See the attached NP246 Tcase writeup. I believe you are getting false information to the Tcase because in order for the vehicle to be truly in 4wd from Tcase to the front wheels the front axles have to be engaged and that would need an active command for 4wd UNLESS you have 2 faults happening and your front axles are engaged at the front diff because of a mechanical failure at the actuator.

We’ll I woke up this morning and the lights on the 4x4 switch were out and message center immediately said service 4x4. Soo looks like it’s electrical? I still haven’t found anywhere that has a code reader fancy enough to read tranny codes.