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.